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L-functions of GL2n: p-adic properties and non-vanishing of twists

Published online by Cambridge University Press:  08 January 2021

Mladen Dimitrov
Affiliation:
Laboratoire Paul Painlevé, CNRS, UMR 8524, University of Lille, 59000Lille, Francemladen.dimitrov@univ-lille.fr
Fabian Januszewski
Affiliation:
Institut für Mathematik, EIM, Paderborn University, Warburger Str. 100, 33098Paderborn, Germanyfabian.januszewski@math.upb.de
A. Raghuram
Affiliation:
Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pashan, Pune411021, Indiaraghuram@iiserpune.ac.in
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Abstract

The principal aim of this article is to attach and study $p$-adic $L$-functions to cohomological cuspidal automorphic representations $\Pi$ of $\operatorname {GL}_{2n}$ over a totally real field $F$ admitting a Shalika model. We use a modular symbol approach, along the global lines of the work of Ash and Ginzburg, but our results are more definitive because we draw heavily upon the methods used in the recent and separate works of all three authors. By construction, our $p$-adic $L$-functions are distributions on the Galois group of the maximal abelian extension of $F$ unramified outside $p\infty$. Moreover, we work under a weaker Panchishkine-type condition on $\Pi _p$ rather than the full ordinariness condition. Finally, we prove the so-called Manin relations between the $p$-adic $L$-functions at all critical points. This has the striking consequence that, given a unitary $\Pi$ whose standard $L$-function admits at least two critical points, and given a prime $p$ such that $\Pi _p$ is ordinary, the central critical value $L(\frac {1}{2}, \Pi \otimes \chi )$ is non-zero for all except finitely many Dirichlet characters $\chi$ of $p$-power conductor.

Type
Research Article
Copyright
© The Author(s) 2021

Introduction

A crucial result in Shimura's work on the special values of $L$-functions of modular forms concerns the existence of a twisting character to ensure that a twisted $L$-value is non-zero at the center of symmetry (see [Reference ShimuraShi77, Theorem 2]). Since then, it has been a very important problem in the analytic theory of automorphic $L$-functions to find characters to render a twisted $L$-value non-zero. Rohrlich [Reference RohrlichRoh89] proved such a non-vanishing result in the context of cuspidal automorphic representations of $\operatorname {GL}_2$ over any number field. This was then generalized to $\operatorname {GL}_N$ over any number field by Barthel and Ramakrishnan [Reference Barthel and RamakrishnanBR94] and further refined by Luo [Reference LuoLuo05]. However, neither [Reference Barthel and RamakrishnanBR94] nor [Reference LuoLuo05] can prove this at the center of symmetry if $N \geqslant 4$ (for us the functional equation will be normalized so that $s = \frac {1}{2}$ is the center of symmetry). There have been other types of analytic machinery that have been brought to bear on this problem, for example, see [Reference Chinta, Friedberg and HoffsteinCFH05]. Even for simple situations involving $L$-functions of higher degree this problem is open. For example, suppose $\pi$ is the unitary cuspidal automorphic representation associated to a primitive holomorphic cusp form for $\operatorname {GL}_2/\mathbb {Q}$, then it has been an open problem to find a Dirichlet character $\chi$ so that the twisted symmetric cube $L$-function $L(\frac {1}{2}, (\operatorname {Sym}^{3}\pi ) \otimes \chi )$ is non-zero at the center.

In this article, we prove the following result.

Theorem A Let $F$ be a totally real field and $\Sigma _\infty$ the set of all its real places. Let $\Pi$ be a unitary cuspidal automorphic representation of $\operatorname {GL}_{2n}/F$ admitting a Shalika model and such that $\Pi _\infty$ is cohomological with respect to a pure dominant integral weight $\mu$ such that

(1)\begin{equation} \mu_{\sigma,n} > \mu_{\sigma, n+1}, \quad \text{for all } \sigma\in \Sigma_\infty. \end{equation}

Assume that for all primes $\mathfrak {p}$ above a given prime number $p$, $\Pi _\mathfrak {p}$ is unramified and $Q$-ordinary, where $Q$ is the parabolic of type $(n,n)$ of $\operatorname {GL}_{2n}/F$ (see (65)).

Then, for all but finitely many Dirichlet characters $\chi$ of $p$-power conductor we have

\[ L\big(\tfrac{1}{2}, \Pi \otimes (\chi\circ \operatorname{N}_{F/\mathbb{Q}}) \big) \neq 0. \]

For notions and notation that are not defined in the introduction, the reader should consult the main body of the paper. A more general statement is proven in Theorem 4.8. Furthermore, we can prove a stronger non-vanishing result covering the nearly ordinary case (see Corollary 4.9) as well as a simultaneous non-vanishing result (see Corollary 4.10). For example, with a classical normalization of $L$-functions, it follows from our results that there are infinitely many Dirichlet characters $\chi$ such that

\[ L(6, \Delta \otimes \chi) \cdot L(17, \operatorname{Sym}^{3}(\Delta) \otimes \chi) \neq 0, \]

for the Ramanujan $\Delta$-function. Our methods are purely arithmetic and involve studying $p$-adic distributions on $\mathscr {C}\!\ell _F^{+}(p^{\infty })$, the Galois group of the maximal abelian extension of $F$ unramified outside $p\infty$, that are attached to suitable eigenclasses in the cohomology of $\operatorname {GL}_{2n}$.

Let us now describe our methods and results in greater detail. We begin with a purely cohomological situation, without any reference to automorphic forms or $L$-functions. Let $\mathcal {O}_{F}$ be the ring of integers of $F$ and $\mathfrak {d}$ its different. Take a pure dominant integral weight $\mu$ for $G = \operatorname {Res}_{\mathcal {O}_{F}/\mathbb {Z}}\operatorname {GL}_{2n},$ and let $V^{\mu }_{E}$ be the algebraic irreducible representation of $G(E)$, for some ‘large enough’ $p$-adic field $E$. If $\mathcal {O}$ is the ring of integers of $E$, then we also consider an $\mathcal {O}$-lattice $V^{\mu }_{\mathcal {O}}$ stabilized by $G(\mathcal {O})$. For any open compact subgroup $K$ of $\operatorname {GL}_{2n}$ over the finite adeles of $F$, let $\mathcal {V}_{\mathcal {O}}^{\mu }$ be the associated sheaf on the locally symmetric space ${S^{G}_K}$ of $G$ with level structure $K$ and let us consider the compactly supported cohomology $\operatorname {H}^{q}_c ({S^{G}_K}, \mathcal {V}_{\mathcal {O}}^{\mu })$ endowed with the usual Hecke action. Assume that for $\mathfrak {p}$ dividing $p$, $K_\mathfrak {p}$ is the parahoric subgroup corresponding to the parabolic $Q$ and consider an eigenclass $\phi \in \operatorname {H}^{t}_c({S^{G}_K}, \mathcal {V}_{\mathcal {O}}^{\mu })$ having a non-zero eigenvalue $\alpha _\mathfrak {p}$ for a particular Hecke operator $U_\mathfrak {p}$. Here and throughout the paper $t= |\Sigma _\infty |(n^{2}+n-1)$ denotes the top degree supporting cuspidal cohomology. The weight $\mu$ determines a contiguous string of integers $\operatorname {Crit}(\mu )$, which would correspond to the set of critical points for an $L$-function. For each $j \in \operatorname {Crit}(\mu )$ we attach an $E$-valued distribution $\boldsymbol {\mu }_{\phi }^{j}$ on $\mathscr {C}\!\ell _F^{+}(p^{\infty })$ and show that it is $\mathcal {O}$-valued when $\phi$ is $Q$-ordinary, that is, it is a measure (see diagram (36) for a quick overview of the sheaf-theoretic maps that are involved in the construction). Most importantly we prove in Theorem 2.3 a Manin-type relation, namely for all $j,j' \in \operatorname {Crit}(\mu )$ we have

\[ \varepsilon_{\operatorname{cyc}}^{j'-j}(\boldsymbol{\mu}^{j}_\phi) = \boldsymbol{\mu}^{j'}_\phi, \]

where $\varepsilon : \mathscr {C}\!\ell _F^{+}(p^{\infty }) \to \mathbb {Z}_p^{\times }$ is the $p$-adic cyclotomic character and $\varepsilon _{\operatorname {cyc}}$ is the automorphism of $\mathcal {O}[[\mathscr {C}\!\ell _F^{+}(p^{\infty })]]$ sending $[x]$ to $\varepsilon ([x])[x]$, allowing us to define a measure $\boldsymbol {\mu }_\phi = \varepsilon _{\operatorname {cyc}}^{-j}(\boldsymbol {\mu }^{j}_\phi )$ that is independent of $j$.

Next we apply these considerations to the situation when $\phi$ is related to a cuspidal automorphic representation $\Pi$ of $\operatorname {GL}_{2n}/F$ such that $\Pi _\infty$ is cohomological with respect to the weight $\mu$ (see § 4.1.3). Friedberg and Jacquet related the period integral of cusp forms in $\Pi$ over the Levi subgroup $H$ of $Q$ to the standard $L$-function $L(s, \Pi )$, and for the unfolding of this integral to see the Eulerian property the representation is assumed to have a Shalika model (see § 4.1). Such a cohomological interpretation was used in [Reference Grobner and RaghuramGR14] to deduce algebraicity results for the critical values of $L(s, \Pi \otimes \chi )$. The following result further investigates their $p$-adic integrality properties. A more general $p$-adic interpolation statement is proven in Theorem 4.7 under the assumption that $\Pi _\mathfrak {p}$ admits a $Q$-regular refinement $\tilde \Pi _\mathfrak {p}$ for $\mathfrak {p}\mid p$ (see Definition 3.5), which is shown to be always fulfilled when $\Pi _\mathfrak {p}$ is $Q$-ordinary (see Lemma 4.4).

Theorem 2 Let $\Pi$ be a cuspidal automorphic representation of $\operatorname {GL}_{2n}/F$ admitting a $(\psi ,\eta )$-Shalika model and such that $\Pi _\infty$ is cohomological of weight $\mu$. Assume that for all primes $\mathfrak {p}$ above a given prime number $p$, $\Pi _\mathfrak {p}$ is spherical and $Q$-ordinary, and let $\alpha _{\mathfrak {p}}$ denote the corresponding $U_{\mathfrak {p}}$-eigenvalue. Given any isomorphism $i_p: \mathbb {C} \xrightarrow {\sim } \bar {\mathbb {Q}}_p$, there exists a bounded $p$-adic distribution $\boldsymbol {\mu }_{\tilde \Pi }$ on $\mathscr {C}\!\ell _F^{+}(p^{\infty })$ such that for any $j\in \operatorname {Crit}(\mu )$ and for any finite order character $\chi$ of $\mathscr {C}\!\ell _F^{+}(p^{\infty })$ of conductor $\beta _\mathfrak {p} \geqslant 1$ at all $\mathfrak {p}\mid p$ one has

\begin{align*} &i_p^{-1}\bigg( \int_{\mathscr{C}\!\ell_F^{+}(p^{\infty})}\varepsilon^{j}(x) \chi(x) \, {d} \boldsymbol{\mu}_{\tilde\Pi}(x)\bigg)\nonumber\\ &\quad = \gamma \cdot \operatorname{N}^{jn}_{F/\mathbb{Q}}(\mathfrak{d}) \cdot \prod_{\mathfrak{p}\mid p} \big (\alpha_{\mathfrak{p}}^{-1} q_\mathfrak{p}^{n(j+1)}\big)^{\beta_\mathfrak{p}} \cdot { \mathcal{G}(\chi_f)^{n} \cdot L\bigg(j+\dfrac{1}{2}, \Pi_f \otimes \chi_f\bigg) } \zeta_\infty\bigg(j+\dfrac{1}{2};W_{\Pi_\infty,j}^{(\varepsilon^{j}\chi\eta)_\infty}\bigg), \end{align*}

where $\mathcal {G}(\chi _f)$ is the Gauss sum, the zeta factor is non-zero by (76), and $\gamma \in \mathbb {Q}^{\times }$ is as in (77).

Let us hint on how we deduce Theorem A. Theorem B, the formulation of which implicitly uses the earlier established Manin relations, gives congruence relations between successive critical values, whereas (1) translates into $\frac {3}{2} \in \operatorname {Crit}(\mu )$. As the complex $L$-function of the unitary cuspidal automorphic representation $\Pi$ does not vanish for $\Re (s) \geqslant 1$ we deduce that $L(\frac {3}{2}, \Pi \otimes \chi )$ never vanishes, which, in turn, implies the non-vanishing of $L(\frac {1}{2}, \Pi \otimes (\chi \circ \operatorname {N}_{F/\mathbb {Q}}))$ for all but finitely many Dirichlet characters $\chi$ (see the proof of Theorem 4.8).

Let us mention some relevant studies in the literature. First, Ash and Ginzburg [Reference Ash and GinzburgAG94] started the study of $p$-adic $L$-functions for $\operatorname {GL}_{2n}$ over a totally real field by considering the analytic theory developed by Friedberg and Jacquet [Reference Friedberg and JacquetFJ93]. However, to quote the authors of [Reference Ash and GinzburgAG94], their results are definitive only for $\operatorname {GL}_4$ over $\mathbb {Q}$ and for cohomology with constant coefficients. Furthermore, they constructed their distributions on local units while only suggesting that one should really work, as we do in this paper, on $\mathscr {C}\!\ell _F^{+}(p^{\infty })$. This article uses the more recent techniques developed in independent papers by all three of the current authors; namely, [Reference DimitrovDim13], [Reference Grobner and RaghuramGR14], and [Reference JanuszewskiJan15]. Finally, we mention Gehrmann's thesis [Reference GehrmannGeh18], which also constructs $p$-adic $L$-functions in essentially a similar context, but his methods are entirely different from ours.

To conclude the introduction, our emphasis is on the purely sheaf-theoretic nature of the construction of the distributions attached to eigenclasses in cohomology, which leads to a purely algebraic proof of Manin relations in a very general context. When specialized to a cohomology class related to a representation $\Pi$ of $\operatorname {GL}_{2n}$, we obtain $p$-adic interpolation of the critical values of the standard $L$-function $L(s, \Pi )$, and Manin relations give non-vanishing of twists $L(s, \Pi \otimes \chi )$ at the center of symmetry. A non-vanishing theorem in the realms of analytic number theory admitting a decidedly algebraic proof is philosophically piquant.

1. Automorphic cohomology

Recall that $F$ is a totally real number field with ring of integers $\mathcal {O}_{F}$ and set of infinite places $\Sigma _\infty$. For a set of places $\Sigma$, we denote by $\mathbb {A}^{(\Sigma )}$ the topological ring of adeles of $\mathbb {Q}$ outside $\Sigma$. Let $\mathbb {A}_F=\mathbb {A}\otimes _{\mathbb {Q}} F$ (respectively, $\mathbb {A}_{F,f}$) be the group of adeles (respectively, finite adeles) of $F$.

We consider $G=\operatorname {Res}_{\mathcal {O}_{F}/\mathbb {Z}}(\operatorname {GL}_{2n})$ as a reductive group scheme over $\mathbb {Z}$, quasi-split over $\mathbb {Q}$ and let $Z=\operatorname {Res}_{\mathcal {O}_{F}/\mathbb {Z}}(\operatorname {GL}_1)$ be the center of $G$. The standard Borel subgroup $B\subseteq G$ is defined as the restriction of scalars of the standard Borel subgroup of all upper triangular matrices in $\operatorname {GL}_{2n}/\mathcal {O}_{F}$. We have $B=TN$, where $N$ is the unipotent radical of $B$ and $T$ is the standard torus of all diagonal matrices. Let $H =\operatorname {Res}_{\mathcal {O}_{F}/\mathbb {Z}}(\operatorname {GL}_n \times \operatorname {GL}_n)$, and $\iota : H \hookrightarrow G$ be the map that sends $(h_1,h_2)$ to $\big (\begin {smallmatrix} h_1 & 0 \\ 0 & h_2 \end {smallmatrix}\big )$. Let $Q=HU$ be the standard parabolic subgroup of type $(n,n)$ whose Levi subgroup is $H$ and unipotent radical is $U$. Finally, the Shalika subgroup $S$ of $G$ is defined as $S=\big \{ \big ( \begin {smallmatrix} h & 0 \\ 0 & h \end {smallmatrix}\big ) \big ( \begin {smallmatrix} 1 & X\\ 0 & 1 \end {smallmatrix}\big ) \mid h\in \operatorname {GL}_n, X\in {\rm M}_n \big \}$.

For any commutative ring $A$, we let ${{\mathfrak {g}}}_A$, ${{\mathfrak {b}}}_A$, ${{\mathfrak {q}}}_A$, ${{\mathfrak {t}}}_A$, ${{\mathfrak {h}}}_A$, ${{\mathfrak {n}}}_A$, and ${{\mathfrak {u}}}_A$ denote the Lie algebras of $G$, $B$, $Q$, $T$, $H$, $N$, and $U$ over $A$, respectively. For ${{\mathfrak {a}}}_A$ any amongst these, we let $\mathcal {U}({{\mathfrak {a}}}_A)$ denote the enveloping algebra over $A$. In the particular case $A=\mathbb {R}$, let ${{\mathfrak {g}}}_\infty ={{\mathfrak {g}}}_{\mathbb {R}} \otimes _{\mathbb {R}} \mathbb {C}$ denote the complexification and likewise for the other groups. The reader is referred to [Reference JantzenJan03] as a general reference for integral Lie algebras and their enveloping algebras.

For any real reductive Lie group $\mathcal {G}$, we let $\mathcal {G}^{\circ }$ denote the connected component of the identity. Let $G_\infty = G(\mathbb {R}),$ and similarly $Z_{\infty } = Z(\mathbb {R})$.

1.1 Pure weights

We identify integral weights $\mu$ of $T$ with tuples of weights $\mu =(\mu _{\sigma })_{\sigma \in \Sigma _\infty },$ $\mu _{\sigma }=(\mu _{\sigma ,1},\ldots ,\mu _{\sigma ,2n})\in \mathbb {Z}^{2n}$. A weight $\mu$ is $B$-dominant if

(2)\begin{equation} \mu_{\sigma,1}\geqslant \cdots \geqslant \mu_{\sigma,2n}, \quad \text{for all} \ \sigma\in \Sigma_\infty. \end{equation}

Let $X^{*}_+(T)$ be the set of all such dominant integral weights. For $\mu \in X^{*}_+(T)$ denote by $V^{\mu }$ the unique algebraic irreducible rational representation of $G$ of highest weight $\mu$. For any field $E$ over which $\mu$ is defined, we denote by $V^{\mu }_{E}$ its $E$-valued points. Denote by $\mu ^{\vee }$ the highest weight of the contragredient $(V^{\mu })^{\vee }$ of $V^{\mu }$ which we consider as a rational character of $B$.

We call $\mu$ pure if there exists ${{\sf w}}\in \mathbb {Z}$, called the purity weight of $\mu$, such that

\[ V^{\mu}=V^{\mu^{\vee}}\otimes (\operatorname{N}_{F/\mathbb{Q}}\circ\det)^{{\sf w}}, \]

where $\operatorname {N}_{F/\mathbb {Q}}:\operatorname {Res}_{F/\mathbb {Q}}(\operatorname {GL}_1)\to \operatorname {GL}_1$ denotes the norm homomorphism. If $\mu$ is pure, then

(3)\begin{equation} \mu_{\sigma, i} + \mu_{\sigma,2n-i+1} = {{\sf w}}, \quad \text{for all } \sigma\in \Sigma_\infty \text{ and for all } 1 \leqslant i \leqslant n. \end{equation}

In particular, $\sum _{i=1}^{2n} \mu _{\sigma ,i}={{\sf w}}n$ is independent of $\sigma$. We let $X^{*}_0(T)\subset X^{*}_+(T)$ denote the pure dominant integral weights of $T$. Given any $\mu \in X^{*}_0(T)$, define the set

(4)\begin{equation} \operatorname{Crit}(\mu) = \{j \in \mathbb{Z} \mid \mu_{\sigma,n} \geqslant j \geqslant \mu_{\sigma,n+1}, \forall \, \sigma\in \Sigma_\infty \}. \end{equation}

It is well known that only pure weights support cuspidal cohomology, and the motivation for this definition comes from the fact proved in [Reference Grobner and RaghuramGR14, Proposition 6.1] that if $\Pi$ is a cuspidal automorphic representation of $G(\mathbb {A})$ that is cohomological with respect to $\mu$ (see § 4.1.3), then $\frac {1}{2}+j$ with $j \in \mathbb {Z}$ is critical for the standard $L$-function $L(s, \Pi \otimes \chi )$ for any finite order character $\chi$ if and only if $j \in \operatorname {Crit}(\mu )$. Note that the central point $({{{\sf w}}+1})/{2}$ of $L(s, \Pi \otimes \chi )$ is critical (i.e. ${{{\sf w}}}/{2}\in \operatorname {Crit}(\mu )$) if and only if ${{\sf w}}$ is even.

1.2 Integral lattices

Let $E$ be a finite extension of $\mathbb {Q}_p$ and let $\mathcal {O}$ be its ring of integers. Given $\mu \in X^{*}_+(T)$, we consider $V^{\mu }_{E}$ as a representation of $G(E)$.

Let $v_0 \in V^{\mu }_{E}$ be a non-zero lowest-weight vector. Then the unipotent radical $N^{-}(E)$ of the Borel subgroup $B^{-}(E)$ of lower triangular matrices fixes $v_0$, whereas $T(E)$ acts on $v_0$ via the character $-\mu ^{\sf v} = w_{2n}(\mu )$ where $w_{2n}$ is the Weyl group element of longest length.

Observe that

(5)\begin{equation} V^{\mu}_{\mathcal{O}} = \mathcal{U}({{\mathfrak{n}}}_\mathcal{O}) v_0, \end{equation}

is an $\mathcal {O}$-lattice $V^{\mu }_{E}$ endowed with a natural action of $G(\mathcal {O})$.

We fix once and for all uniformizers $\varpi _{\mathfrak {p}}\in F_{\mathfrak {p}}$ and put $t_{\mathfrak {p}} = \iota (\varpi _{\mathfrak {p}}\cdot \textbf {1}_n,\textbf {1}_n) \in \operatorname {GL}_{2n}(F_{\mathfrak {p}})$. Define for any integral multi-exponent $\beta =(\beta _{\mathfrak {p}})_{\mathfrak {p}\mid p}$ the element

(6)\begin{equation} t_p^{\beta}=\prod_{\mathfrak{p}\mid p}t_{\mathfrak{p}}^{\beta_{\mathfrak{p}}}\in T(\mathbb{Q}_p), \end{equation}

and consider the semi-group

(7)\begin{equation} \Delta_p^{+}=\{t_p^{\beta} \mid \beta_{\mathfrak{p}}\in \mathbb{Z}_{\geqslant 0}, \ \forall\,\mathfrak{p}\mid p\}. \end{equation}

Then by our choice of dominance condition, we have for any $t\in \Delta _p^{+}$:

(8)\begin{equation} {\operatorname{Ad}}(t)Q(\mathcal{O})=tQ(\mathcal{O})t^{-1}\subseteq Q(\mathcal{O}) \quad \text{and}\quad {\operatorname{Ad}}(t^{-1})U^{-}(\mathcal{O})=t^{-1}U^{-}(\mathcal{O}) t\subseteq U^{-}(\mathcal{O}). \end{equation}

Consider the standard maximal parahoric subgroup $J_p=\prod _{\mathfrak {p}\mid p} J_\mathfrak {p}\subset G(\mathbb {Z}_p)$, where

(9)\begin{equation} J_\mathfrak{p}=t_\mathfrak{p}^{-1}\operatorname{GL}_{2n}(\mathcal{O}_{F,\mathfrak{p}}) t_\mathfrak{p}\cap \operatorname{GL}_{2n}(\mathcal{O}_{F,\mathfrak{p}}). \end{equation}

As $J_p \supset Q(\mathbb {Z}_p)$, the parahoric decomposition is given by

(10)\begin{equation} J_p= (J_p\cap U^{-}(\mathbb{Z}_p))Q(\mathbb{Z}_p)=Q(\mathbb{Z}_p)(J_p \cap U^{-}(\mathbb{Z}_p)). \end{equation}

Using (8) and (10) one sees that

(11)\begin{equation} \Lambda_p=J_p \Delta_p^{+} J_p= Q(\mathbb{Z}_p) \Delta_p^{+} (J_p\cap U^{-}(\mathbb{Z}_p)), \end{equation}

is a semi-group. Moreover, because $U^{-}(\mathbb {Z}_p)\subset N^{-}(\mathbb {Z}_p)$ acts trivially on $v_0$, the $J_p$-action on $V^{\mu }_{\mathcal {O}}$ extends uniquely to an action $\bullet$ of the semi-group $\Lambda _p$ by letting $\Delta _p^{+}$ act trivially on the lowest weight vector $v_0$. Then for all $t\in \Delta _p^{+}$ and $v\in V^{\mu }_{\mathcal {O}}$ one has

(12)\begin{equation} t\bullet v= \mu^{\vee}(t) (t\cdot v). \end{equation}

In fact, by (5), one can write $v=m\cdot v_0$ for some $m\in \mathcal {U}({{\mathfrak {n}}}_\mathcal {O})$ and using (8) one finds

\[ t\bullet v= t\bullet (m\bullet v_0) = {\operatorname{Ad}}(t)(m)\bullet(t\bullet v_0)={\operatorname{Ad}}(t)(m)\cdot v_0=\mu^{\vee}(t) {\operatorname{Ad}}(t)(m)(t\cdot v_0)=\mu^{\vee}(t) (t\cdot v). \]

1.3 Local systems on locally symmetric spaces for GL2n

The standard maximal compact subgroup of $G_\infty$ is denoted by $C_{\infty }=\prod _{\sigma \in \Sigma _\infty }C_\sigma$, where $C_{\sigma }\simeq {\rm O}_{2n}(\mathbb {R})$. The determinant identifies the group of connected components $C_{\infty }/C_{\infty }^{\circ }$ with $F_{\infty }^{\times }/F_{\infty }^{\times \circ }\cong \{\pm 1\}^{\Sigma _\infty }$. Let $K_\infty =C_{\infty } Z_{\infty }$ and for any open compact subgroup $K$ of $G(\mathbb {A}_f)$ consider the locally symmetric space:

(13)\begin{equation} {S^{G}_K}= G(\mathbb{Q})\backslash G(\mathbb{A})/K K_{\infty}^{\circ} = G(\mathbb{Q})\backslash \big((G_\infty/ K_{\infty}^{\circ}) \times G(\mathbb{A}_f)/K\big). \end{equation}

Note that $K_{\infty }^{\circ } = C_{\infty }^{\circ } Z_{\infty }^{\circ }=C_{\infty }^{\circ } Z_{\infty }$ because $2n$ is even. In general, ${S^{G}_K}$ is only a real orbifold. In the sequel, we assume that $K$ is sufficiently small in the sense that for all $g\in G(\mathbb {A})$,

(14)\begin{equation} G(\mathbb{Q})\cap gKK_{\infty}^{\circ} g^{-1}= Z(\mathbb{Q})\cap KK_{\infty}^{\circ} , \end{equation}

which implies in particular that ${S^{G}_K}$ is a real manifold.

Given a left $G(\mathbb {Q})$-module $V\!$, one can define $\mathcal {V}_K$ as the sheaf of locally constant sections of the local system:

\[ G(\mathbb{Q})\backslash (G(\mathbb{A}) \times V )/KK_{\infty}^{\circ} \to {S^{G}_K}, \]

where $\gamma (g,v)k=(\gamma g k,\gamma \cdot v)$ for all $\gamma \in G(\mathbb {Q})$, $k\in K K_{\infty }^{\circ }$. Consider the canonical fibration $\pi : (G(\mathbb {R})/ K_{\infty }^{\circ } ) \times G(\mathbb {A}_f)/K \to {S^{G}_K}$ given by going modulo the left action of $G(\mathbb {Q})$. Then, for any open $\mathcal {U} \subset {S^{G}_K}$, one has the sections $\mathcal {V}_K(\mathcal {U})$ over $\mathcal {U}$ to be the set of all locally constant $s : \pi ^{-1}(\mathcal {U}) \to V$ such that $s(\gamma \cdot x) = \gamma \cdot s(x)$ for all $\gamma \in G(\mathbb {Q}), x \in \pi ^{-1}(\mathcal {U}).$ We denote by $\mathcal {V}_{K,E}^{\mu }$ the sheaf associated to $V^{\mu }_{E}$. The sheaf $\mathcal {V}_{K,E}^{\mu }$ is non-trivial if and only if

(15)\begin{equation} \mu(Z(\mathbb{Q})\cap K K_{\infty}^{\circ} )=\{1\}. \end{equation}

Condition (15) is always satisfied if $\mu$ is pure, because $\det (F^{\times } \cap K K_{\infty }^{\circ } )\subset \mathcal {O}_{F}^{\times }\cap F_{\infty }^{\times \circ }$.

In order to attach a sheaf to $V^{\mu }_{\mathcal {O}}$ we need a slightly different construction. Given a left $K$-module $V$ satisfying (15) define $\mathcal {V}_K$ instead as the sheaf of locally constant sections of

\[ G(\mathbb{Q})\backslash (G(\mathbb{A})\times V) /K K_{\infty}^{\circ} \to Y_K, \]

with left $G(\mathbb {Q})$-action and right $K K_{\infty }^{\circ }$-action given by $\gamma (g,v)k=(\gamma g k , k^{-1}\cdot v)$. As $K$ acts on $V^{\mu }_{\mathcal {O}}$ through its $p$-component $K_p\subset G(\mathbb {Z}_p)\subset G(\mathcal {O})$ we obtain a sheaf $\mathcal {V}_{\mathcal {O}}^{\mu }$ on ${S^{G}_K}$.

When the actions of $G(\mathbb {Q})$ and $K$ on $V$ extend compatibly into a left action of $G(\mathbb {A})$, the two resulting local systems are isomorphic by $(g,v)\mapsto (g,g^{-1}\cdot v)$, justifying the abuse of notation.

1.4 Hecke operators

For any open compact subgroups $K'\subseteq K$ of $G(\mathbb {A}_f)$ the natural map $p_{K',K} : S^{G}_{K'}\to {S^{G}_K}$ induces an isomorphism of sheaves $p_{K',K}^{*}\mathcal {V}_K\overset {\sim }{\to } \mathcal {V}_{K'}$.

When the $K$-action on $V$ extends to an action of a semi-group containing $K$ and $\gamma$, then one can define a Hecke operator $[K\gamma K]$ as a composition of three maps:

\[ [K\gamma K]=\mathrm{Tr}(p_{\gamma K\gamma^{-1}\cap K,K})\circ [\gamma] \circ p_{K\cap \gamma^{-1}K\gamma,K}^{*} :\quad \operatorname{H}_c^{q}({S^{G}_K},\mathcal{V}_K) \to \operatorname{H}_c^{q}({S^{G}_K},\mathcal{V}_K), \]

where $p_{K\cap \gamma ^{-1}K\gamma ,K}^{*}$ is the pull-back, $\mathrm {Tr}(p_{\gamma K\gamma ^{-1}\cap K,K})$ is the finite flat trace and

\[ [\gamma]:\operatorname{H}_c^{q}(S^{G}_{K\cap \gamma^{-1}K\gamma},\mathcal{V}_{K\cap \gamma^{-1}K\gamma})\to \operatorname{H}_c^{q}(S^{G}_{\gamma K\gamma^{-1}\cap K},\mathcal{V}_{\gamma K\gamma^{-1}\cap K}), \]

is induced by the morphism of local systems given by $(g,v)\mapsto (g\gamma ^{-1}, \gamma \cdot v)$ in the case of a right $K$-action.

When $K_p\subset J_p$, the above construction applies to $V^{\mu }_{\mathcal {O}}$ on which the semi-group $\Lambda _p$ acts by the $\bullet$-action (see (11)) yielding for each $t\in \Delta _p^{+}$ a Hecke operator $[KtK]$ on $\operatorname {H}_c^{q}({S^{G}_K},\mathcal {V}_{K,\mathcal {O}}^{\mu })$. Note that although the natural inclusion $V^{\mu }_{\mathcal {O}}\subseteq V^{\mu }_{E}$ is $K_p$-equivariant, it is not $\Lambda _p$-equivariant (see (12)). As a consequence, the natural map $\operatorname {H}_c^{q}({S^{G}_K},\mathcal {V}_{K,\mathcal {O}}^{\mu })\to \operatorname {H}_c^{q}({S^{G}_K},\mathcal {V}_{K,E}^{\mu })$ is equivariant for the $\bullet$-action of $[KtK]$ on the source and the action of the optimally integral Hecke operator $[KtK]^{\circ }=\mu ^{\vee }(t)[KtK]$ on the target. To ensure compatibility with extension of scalars, we also denote by $[KtK]^{\circ }$ the Hecke operator $[KtK]$ acting (via the $\bullet$-action) on $\operatorname {H}_c^{q}({S^{G}_K},\mathcal {V}_{K,\mathcal {O}}^{\mu })$.

For any prime $\mathfrak {p}\mid p$ of $F$, the following Hecke operators play an important role:

(16)\begin{equation} U_{\mathfrak{p}} = [K t_\mathfrak{p} K] \quad \text{and}\quad U_\mathfrak{p}^{\circ}=\mu^{\vee}(t_\mathfrak{p}) U_\mathfrak{p}. \end{equation}

For $\beta =(\beta _\mathfrak {p})_{\mathfrak {p}\mid p}$ with $\beta _\mathfrak {p}\in \mathbb {Z}_{\geqslant 0}$ we let $U_{p^{\beta }} = [K t_{p^{\beta }} K]$ and $U_{p^{\beta }}^{\circ }=\mu ^{\vee }(t_{p^{\beta }}) U_{p^{\beta }}.$

As the image of $\operatorname {H}^{q}_c({S^{G}_K}, \mathcal {V}_{\mathcal {O}}^{\mu })$ in $\operatorname {H}^{q}_c({S^{G}_K}, \mathcal {V}_{E}^{\mu })$ is a finitely generated $\mathcal {O}$-module, we may assume that $E$ is large enough so that all $U_{\mathfrak {p}}^{\circ }$-eigenvalues belong to $\mathcal {O}$.

2. Distributions attached to cohomology classes for GL2n

Let $F_p=F\otimes _\mathbb {Q}\mathbb {Q}_p=\prod _{\mathfrak {p} \mid p}F_{\mathfrak {p}}$. For a prime $\mathfrak {p}\mid p$ of $F$ we denote by $I_\mathfrak {p}$ (respectively, $J_\mathfrak {p}$) the standard Iwahori (respectively, parahoric) subgroup of $K_\mathfrak {p}^{\circ }=\operatorname {GL}_{2n}(\mathcal {O}_{F,\mathfrak {p}})$ consisting of elements whose reduction modulo the $\mathfrak {p}$ belongs to $B(\mathcal {O}_{F}/{\mathfrak {p}})$ (respectively, to $Q(\mathcal {O}_{F}/{\mathfrak {p}})$).

We let $K=K^{(p)}\times \prod _{\mathfrak {p}\mid p}K_\mathfrak {p}$ be an open compact subgroup of $G(\mathbb {A}_f)$ such that:

  1. (K1) $K^{(p)}$ is the principal congruence subgroup of modulus $\mathfrak {m}$, an ideal of $\mathcal {O}_F$ which is relatively prime to $p$, and $K^{(p)}G(\mathbb {Z}_p)$ satisfies (14);

  2. (K2) $\big (\begin {smallmatrix} T_n(\mathcal {O}_{F,\mathfrak {p}}) & M_n(\mathcal {O}_{F,\mathfrak {p}}) \\ \textbf {0}_n & T_n(\mathcal {O}_{F,\mathfrak {p}}) \end {smallmatrix}\big ) \subseteq K_\mathfrak {p} \subseteq J_\mathfrak {p}$ for all $\mathfrak {p} \mid p$.

An important role will be played by the matrix $\xi \in \operatorname {GL}_{2n}(\mathbb {A}_F)$, where

(17)\begin{equation} \xi_{\mathfrak{p}}= \begin{pmatrix}\textbf{1}_n & w_n\\ \textbf{0}_n & w_n\end{pmatrix}\in \operatorname{GL}_{2n}(\mathcal{O}_{F,\mathfrak{p}}), \quad \text{for all } \mathfrak{p}\mid p , \quad \text{and}\quad \xi_v=\textbf{1}_{2n}, \quad \text{for all } v\nmid p. \end{equation}

Here $\textbf {1}_n$ and $\textbf {0}_n$ are the $n \times n$ identity and zero matrices, respectively, and $w_n$ is the longest length element in the Weyl group of $\operatorname {GL}_n,$ whose $(i,j)$-entry is $\delta _{i, n-j+1}$.

We have $\xi _{\mathfrak {p}}^{-1} = \big (\begin {smallmatrix} \textbf {1}_n & -\textbf {1}_n\\ \textbf {0}_n & w_n \end {smallmatrix}\big )$. Once and for all we record the identities

(18)\begin{equation} \xi_{\mathfrak{p}}^{-1}\cdot\begin{pmatrix}A & B\\ C & D\end{pmatrix}\cdot\xi_{\mathfrak{p}} = \begin{pmatrix}A-C & (A-D+B-C)w_n \\ w_n C & w_n (C+D) w_n\end{pmatrix} \end{equation}

and

(19)\begin{equation}\xi_{\mathfrak{p}}\cdot\begin{pmatrix}A & B\\ C & D\end{pmatrix}\cdot\xi_{\mathfrak{p}}^{-1} = \begin{pmatrix}A+w_nC & w_n D w_n-A+Bw_n-w_nC \\ w_n C & w_n D w_n-w_nC\end{pmatrix}. \end{equation}

2.1 Automorphic cycles

For any open-compact subgroup $L \subset H(\mathbb {A}_f)$ we consider the locally symmetric space:

(20)\begin{equation} \tilde{S}^{H}_L = H(\mathbb{Q}) \backslash H(\mathbb{A}) / L L_\infty^{\circ}, \quad \text{where } L_\infty=H_\infty \cap K_{\infty} . \end{equation}

Note that for each $\sigma \in \Sigma _\infty$ one has $L_\sigma ^{\circ } \simeq \big (\begin {smallmatrix}\operatorname {SO}_{n}(\mathbb {R}) & 0 \\ 0 & \operatorname {SO}_{n}(\mathbb {R}) \end {smallmatrix}\big )\mathbb {R}^{\times \circ }$. As in (14), $\tilde {S}^{H}_L$ is a real manifold when $L$ is sufficiently small in the sense that for all $h\in H(\mathbb {A})$,

(21)\begin{equation} H(\mathbb{Q})\cap h LL_{\infty}^{\circ} h^{-1}= Z(\mathbb{Q})\cap LL_{\infty}^{\circ}. \end{equation}

Recall the notation $t_{\mathfrak {p}}= \iota (\varpi _{\mathfrak {p}}\cdot \textbf {1}_n,\textbf {1}_n)$ where $\varpi _{\mathfrak {p}}$ is an uniformizer at $\mathfrak {p}\mid p$. Recall also that for $\beta =(\beta _{\mathfrak {p}})_{\mathfrak {p}\mid p}$ with $\beta _\mathfrak {p}\in \mathbb {Z}_{\geqslant 0}$ we let $p^{\beta }=\prod _{\mathfrak {p}\mid p}\varpi _{\mathfrak {p}}^{\beta _{\mathfrak {p}}}$ and $t_p^{\beta } = \prod _{\mathfrak {p}\mid p} t_{\mathfrak {p}}^{\beta _{\mathfrak {p}}} \in G(\mathbb {Q}_p)$.

For any ideal $\mathfrak {m}$ of $\mathcal {O}_F$, we denote by $I(\mathfrak {m})$ the open-compact subgroup of $\mathbb {A}_{F,f}^{\times }$ of modulus $\mathfrak {m}$, and we consider the strict idele class group:

\[ \mathscr{C}\!\ell_F^{+}(\mathfrak{m})= F^{\times}\backslash \mathbb{A}_F^{\times}/I(\mathfrak{m}) F_\infty^{\times\circ}. \]

We let $L_\beta = L^{(p)} \prod _{\mathfrak {p}\mid p} L_\mathfrak {p}^{\beta _\mathfrak {p}}$ be an open compact subgroup of $H(\mathbb {A}_f)$ such that:

  1. (L1) $L^{(p)}=K^{(p)}\cap H$ is the principal congruence subgroup of modulus $\mathfrak {m}$; and

  2. (L2) $L_\mathfrak {p}^{\beta _\mathfrak {p}}=H(F_\mathfrak {p})\cap K_\mathfrak {p}\cap \xi t_{\mathfrak {p}}^{\beta _\mathfrak {p}}K_\mathfrak {p} t_{\mathfrak {p}}^{-\beta _\mathfrak {p}}\xi ^{-1}$ for all $\mathfrak {p} \mid p$.

Note that conditions (K1) and (L1) imply (21), in particular that $\tilde {S}^{H}_{L_\beta }$ is a real manifold.

Lemma 2.1 $L_\mathfrak {p}^{\beta _\mathfrak {p}}$ consists of elements $(h_1 , h_2)\in \operatorname {GL}_n(\mathcal {O}_{F,\mathfrak {p}})\times \operatorname {GL}_n(\mathcal {O}_{F,\mathfrak {p}})$ such that

\[ \iota(h_1, h_2) \in K_\mathfrak{p} \cap \begin{pmatrix}\mathbf{1}_n & \\ & w_n \end{pmatrix} K_\mathfrak{p} \begin{pmatrix}\mathbf{1}_n & \\ & w_n \end{pmatrix}, \quad \text{and} \quad h_1h_2^{-1} \in 1+ \varpi_\mathfrak{p}^{\beta_\mathfrak{p}}M_n(\mathcal{O}_{F,\mathfrak{p}}). \]

Proof. By (18) for all $(h_1,h_2) \in H(F_\mathfrak {p})\cap K_\mathfrak {p}=\operatorname {GL}_n(\mathcal {O}_{F,\mathfrak {p}})\times \operatorname {GL}_n(\mathcal {O}_{F,\mathfrak {p}})$ one has

\[ t_{\mathfrak{p}}^{-\beta_{\mathfrak{p}}} \xi^{-1} \begin{pmatrix}h_1 & \\ & h_2 \end{pmatrix}\xi t_{\mathfrak{p}}^{\beta_{\mathfrak{p}}}=\begin{pmatrix}h_1 & \varpi^{-\beta_{\mathfrak{p}}}(h_1 - h_2)w_n \\ & w_n h_2 w_n \end{pmatrix}. \]

Hence, $h_1- h_2 \in \varpi _\mathfrak {p}^{\beta _\mathfrak {p}}M_n(\mathcal {O}_{F,\mathfrak {p}})$, and as $\big (\begin {smallmatrix}\textbf {1}_n & M_n(\mathcal {O}_{F,\mathfrak {p}}) \\ \textbf {0}_n & \textbf {1}_n \end {smallmatrix}\big ) \subseteq K_\mathfrak {p}$, we obtain $(h_1,w_n h_2 w_n)\in K_\mathfrak {p}$.

Lemma 2.1 implies that the map $(1+ \varpi _\mathfrak {p}^{\beta _\mathfrak {p}}M_n(\mathcal {O}_{F,\mathfrak {p}}))\times \mathcal {O}_{F,\mathfrak {p}}^{\times } \to \det (L_\mathfrak {p}^{\beta _\mathfrak {p}})$ sending $(x,y)$ to $(xy,y)$ is an isomorphism. By the strong approximation theorem for $\operatorname {SL}_{n}(\mathbb {A}_F)$ the map

\[ (h_1,h_2) \mapsto \bigg( \frac{\det(h_1)}{\det(h_2)}, \det(h_2) \bigg), \]

identifies the set of connected components of $\tilde {S}^{H}_{L_\beta }$ with a product of two idele class groups:

(22)\begin{equation} \pi_0(\tilde{S}^{H}_{L_\beta}) \overset{\sim}{\longrightarrow} \mathscr{C}\!\ell_F^{+}(p^{\beta} \mathfrak{m}) \times \mathscr{C}\!\ell_F^{+}(\mathfrak{m}). \end{equation}

It is easy to see that the fiber $\tilde {S}^{H}_{L_\beta }[\delta ]$ of $[\delta ]\in \pi _0(\tilde {S}^{H}_{L_\beta })$ is connected of dimension

(23)\begin{equation} t= |\Sigma_\infty|(n^{2}+n-1). \end{equation}

If we consider a cohomology class on ${S^{G}_K}$ in degree $t$, and pull it back to $\tilde {S}^{H}_{L_\beta }[\delta ]$, then we end up with a top-degree class. The degree $t$ happens to be the top-most degree with non-vanishing cuspidal cohomology of ${S^{G}_K}$. This magical numerology is at the heart of what ultimately permits us to give a cohomological interpretation to an integral representing an $L$-value (see [Reference Grobner and RaghuramGR14]) and allows us to study its $p$-adic properties.

2.2 Evaluation maps

Fix $\mu \in X^{*}_0(T)$.

2.2.1 Automorphic symbols

By condition (L2), the map

(24)\begin{equation} \iota_\beta : \tilde{S}^{H}_{L_\beta} \rightarrow {S^{G}_K}, \quad [h] \mapsto [\iota(h)\xi t_p^{\beta}], \end{equation}

is well-defined. As $\iota _\beta$ is proper by a well-known result of Borel and Prasad (see, for example, [Reference AshAsh80, Lemma 2.7]) one can consider the pull-back:

(25)\begin{equation} \iota_\beta^{*} : \operatorname{H}^{q}_c({S^{G}_K}, \mathcal{V}_{\mathcal{O}}^{\mu}) \longrightarrow \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}, \iota_\beta^{*}\mathcal{V}_{\mathcal{O}}^{\mu}). \end{equation}

2.2.2 Twisting

By condition (L1), the map $\iota : \tilde {S}^{H}_{L_\beta } \to {S^{G}_K}$, $[h]\mapsto [\iota (h)]$ is well-defined and proper. As $\xi t_p^{\beta }\in \Lambda _p$, using the $\bullet$-action from (12) one can consider the map

\[ H(\mathbb{A})\times V_{\mathcal{O}}^{\mu}\to H(\mathbb{A})\times V_{\mathcal{O}}^{\mu}, \quad (h,v)\mapsto (h, (\xi t_p^{\beta})\bullet v), \]

inducing a homomorphism of sheaves $\tau _\beta ^{\circ } : \iota _\beta ^{*}\mathcal {V}_{\mathcal {O}}^{\mu } \longrightarrow \iota ^{*}\mathcal {V}_{\mathcal {O}}^{\mu }$, hence a map in cohomology

(26)\begin{equation} \tau_\beta^{\circ} : \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}, \iota_\beta^{*}\mathcal{V}_{\mathcal{O}}^{\mu}) \longrightarrow \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}, \iota^{*}\mathcal{V}_{\mathcal{O}}^{\mu}). \end{equation}

Similarly, using the natural action of $G(E)$ on $V_{E}^{\mu }$ instead of the $\bullet$-action one defines a map

(27)\begin{equation} \tau_\beta : \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}, \iota_\beta^{*}\mathcal{V}_{E}^{\mu}) \longrightarrow \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}, \iota^{*}\mathcal{V}_{E}^{\mu}), \end{equation}

and $\tau _\beta =\mu ^{\vee }(t_p^{-\beta })\tau _\beta ^{\circ }$, because by (12) one has $(\xi t_p^{\beta }) \bullet v= \mu ^{\vee }(t_p^{\beta }) (\xi t_p^{\beta })\cdot v$ for all $v\in V_{E}^{\mu }$.

2.2.3 Critical maps

For $j_1,j_2 \in \mathbb {Z}$ let $V^{(j_1,j_2)}$ be the $1$-dimensional $H$-representation

\[ (h_1,h_2) \mapsto \operatorname{N}_{F/\mathbb{Q}}(\det(h_1)^{j_1} \det(h_2)^{j_2}). \]

Let $V^{(j_1,j_2)}_{\mathcal {O}}$ be a free rank one $\mathcal {O}$-module on which the previously defined natural $H(\mathbb {Z}_p)$-action is extended to a $H(\mathbb {Q}_p)$-action by letting $p\in \mathbb {Q}_p^{\times }$ act trivially. Note that this action is similar to the $\Lambda _p$-action on $V^{\mu }_{\mathcal {O}}$ defined in § 1.2.

It follows from [Reference Grobner and RaghuramGR14, Proposition 6.3] that $j \in \operatorname {Crit}(\mu )$ (see (4)) if and only if

(28)\begin{equation} \dim(\operatorname{Hom}_H(V^{\mu}, V^{(j,{{\sf w}}-j)}) ) = 1. \end{equation}

Fix a non-zero $\kappa _j \in \operatorname {Hom}_H(V^{\mu }, V^{(j,{{\sf w}}-j)})$ normalized so as to obtain an integral map:

\[ \kappa_j : V^{\mu}_{\mathcal{O}} \rightarrow V^{(j,{{\sf w}}-j)}_{\mathcal{O}}. \]

Denoting by $\mathcal {V}^{(j,{{\sf w}}-j)}_{\mathcal {O}}$ the sheaf on $\tilde {S}^{H}_{L_\beta }$ attached to $V^{(j,{{\sf w}}-j)}_{\mathcal {O}}$ by the construction described in § 1.3, one obtains a homomorphism:

(29)\begin{equation} \kappa_j : \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}, \iota^{*}\mathcal{V}_{\mathcal{O}}^{\mu}) \longrightarrow \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}, \mathcal{V}^{(j,{{\sf w}}-j)}_{\mathcal{O}}). \end{equation}

Putting (25), (26) and (29) together, for each $j \in \operatorname {Crit}(\mu )$, we obtain a map:

(30)\begin{equation} \kappa_j \circ \tau_\beta^{\circ}\circ \iota_\beta^{*} : \operatorname{H}^{q}_c({S^{G}_K}, \mathcal{V}_{\mathcal{O}}^{\mu}) \longrightarrow \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}, \mathcal{V}^{(j,{{\sf w}}-j)}_{\mathcal{O}}). \end{equation}

2.2.4 Trivializations

Given any $\delta \in H(\mathbb {A}_f)$ the map

\[ \operatorname{triv}_\delta:H(\mathbb{Q})\delta L_\beta H_\infty^{\circ}\times V^{(j,{{\sf w}}-j)}_{\mathcal{O}}\to H(\mathbb{Q})\delta L_\beta H_\infty^{\circ}\times V^{(j,{{\sf w}}-j)}_{\mathcal{O}}\, , \, (\gamma\delta l h_\infty, v)\mapsto (\gamma\delta l h_\infty, l_p^{-1}\cdot v), \]

is well-defined because $H(\mathbb {Q})\cap L_\beta H_\infty ^{\circ }\subset \ker (\operatorname {N}_{F/\mathbb {Q}}\circ \det )$ acts trivially on $V^{(j,{{\sf w}}-j)}_{\mathcal {O}}$. An easy check shows that $\operatorname {triv}_\delta$ induces a homomorphism of local systems

\[ \tilde{S}^{H}_{L_\beta}[\delta] \times V^{(j,{{\sf w}}-j)}_{\mathcal{O}}\to \big(\mathcal{V}^{(j,{{\sf w}}-j)}_{\mathcal{O}}\big)|_{\tilde{S}^{H}_{L_\beta}[\delta]}, \]

where $[\delta ]$ denotes the image of $\delta$ in $\pi _0(\tilde {S}^{H}_{L_\beta })$, hence yields a homomorphism:

\[ \operatorname{triv}_\delta^{*}: \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}[\delta], \mathcal{V}^{(j,{{\sf w}}-j)}_{\mathcal{O}}) \to \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}[\delta], \mathbb{Z})\otimes V^{(j,{{\sf w}}-j)}_{\mathcal{O}}. \]

We now render the trivializations independent of the choice of $\delta \in [\delta ]\in \pi _0(\tilde {S}^{H}_{L_\beta })$. By definition, for any $\delta '\in H(\mathbb {Q}) \delta l H_\infty$ one has

(31)\begin{equation} \operatorname{triv}_{\delta'}^{*}= (\operatorname{id}\otimes l_p^{-1})\cdot \operatorname{triv}_{\delta}^{*}=\operatorname{N}_{F_p/\mathbb{Q}_p}^{-1} \big(\det(l_{1,p})^{j}\det(l_{2,p})^{{{\sf w}}-j}\big)\operatorname{triv}_{\delta}^{*}. \end{equation}

The $p$-adic cyclotomic character $\varepsilon$ seen as idele class character $F^{\times } \backslash \mathbb {A}_F^{\times } \to \mathbb {Z}_p^{\times }$ sends $y$ to $\operatorname {N}_{F_p/\mathbb {Q}_p}(y_p)|y_f|_F\prod _{\sigma \in \Sigma _\infty } {\rm sgn}(y_\sigma )$, is trivial on $F_\infty ^{\times \circ }$ and given by $\operatorname {N}_{F_p/\mathbb {Q}_p}$ on $(\mathcal {O}_{F}\otimes \mathbb {Z}_p)^{\times }$. Hence,

(32)\begin{equation} \operatorname{triv}_{[\delta]}^{*}= \varepsilon \big(\det(\delta_{1}^{j}\delta_{2}^{{{\sf w}}-j})\big) \operatorname{triv}_\delta^{*} : \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}[\delta], \mathcal{V}^{(j,{{\sf w}}-j)}_{\mathcal{O}}) \to \operatorname{H}^{q}_c(\tilde{S}^{H}_{L_\beta}[\delta], \mathbb{Z})\otimes V^{(j,{{\sf w}}-j)}_{\mathcal{O}}, \end{equation}

is independent of the particular choice of $\delta \in [\delta ]\in \pi _0(\tilde {S}^{H}_{L_\beta })$.

2.2.5 Connected components and fundamental classes

Recall that for each $[\delta ]\in \pi _0(\tilde {S}^{H}_{L_\beta })$, $\tilde {S}^{H}_{L_\beta }[\delta ]$ is a $t$-dimensional connected orientable real manifold and that choosing an orientation amounts to choosing a fundamental class, that is, a basis $\theta _{[\delta ]}$ of its Borel–Moore homology $H_{t}^{\mathrm {BM}}(\tilde {S}^{H}_{L_\beta }[\delta ])\simeq \mathbb {Z}$. We choose such orientations in a consistent manner when $\beta$ and $[\delta ]$ vary as follows. First, we fix, once and for all, an ordered basis on the tangent space of the symmetric space $H_\infty ^{\circ }/L_\infty ^{\circ }$ yielding fundamental classes $\theta _{\beta }$ of the connected components of identity $\tilde {S}^{H}_{L_\beta }[1]$, when $\beta$ varies. Then for each $[\delta ]\in \pi _0(\tilde {S}^{H}_{L_\beta })$, we consider the isomorphism $\tilde {S}^{H}_{L_\beta }[1]\underset {\sim }{\overset {\cdot \delta }{\longrightarrow }} \tilde {S}^{H}_{L_\beta }[\delta ]$ and define $\theta _{[\delta ]}=\delta _*\theta _{\beta }$, which is clearly independent of the particular choice of $\delta \in [\delta ]$. Capping with $\theta _{[\delta ]}$ and fixing a basis of $V^{(j,{{\sf w}}-j)}_{\mathcal {O}}$ (later in (40) we fix a particular basis in order to compare evaluations at different $j$) yields an isomorphism:

\[ \operatorname{H}^{t}_c(\tilde{S}^{H}_{L_\beta}[\delta], \mathbb{Z})\otimes V^{(j,{{\sf w}}-j)}_{\mathcal{O}} \overset{\sim}{\longrightarrow} V^{(j,{{\sf w}}-j)}_{\mathcal{O}}\overset{\sim}{\longrightarrow} \mathcal{O}. \]

Combining this with (30) and (32) gives homomorphisms:

(33)\begin{align} \begin{aligned} \mathcal{E}^{j,{{\sf w}}}_{\beta,\delta}&=(\!\cap \theta_{[\delta]}) \circ\operatorname{triv}_\delta^{*}\circ\kappa_j \circ \tau_\beta^{\circ}\circ \iota_\beta^{*}: \operatorname{H}^{t}_c({S^{G}_K}, \mathcal{V}_{\mathcal{O}}^{\mu})\to \mathcal{O},\\ \mathcal{E}^{j,{{\sf w}}}_{\beta, [\delta]}&= \varepsilon \big(\det(\delta_{1}^{j}\delta_{2}^{{{\sf w}}-j})\big) \cdot \mathcal{E}^{j,{{\sf w}}}_{\beta,\delta}=(\!\cap \theta_{[\delta]}) \circ \operatorname{triv}_{[\delta]}^{*} \circ\kappa_j \circ \tau_\beta^{\circ}\circ \iota_\beta^{*} : \operatorname{H}^{t}_c({S^{G}_K}, \mathcal{V}_{\mathcal{O}}^{\mu})\to \mathcal{O}.\end{aligned} \end{align}

2.2.6 Summing over the second component

Consider a finite order $\mathcal {O}$-valued idele class character $\eta _0$ of $F$ that is trivial on $I(\mathfrak {m})$, in particular unramified at all places above $p$. The character $\eta =\eta _0|\cdot |_F^{-{{\sf w}}}$ later plays a role when we discuss Shalika models for automorphic representations of $G$. The following map provides a section of (22):

(34)\begin{equation} \delta(x,y) = (\operatorname{diag}(xy, 1,\ldots, 1), \operatorname{diag}(y, 1,\ldots ,1)) \in H. \end{equation}

When $(x,y)\in (\mathbb {A}_F^{\times })^{2}$ runs over a set of representatives of $\mathscr {C}\!\ell _F^{+}(p^{\beta }\mathfrak {m})\times \mathscr {C}\!\ell _F^{+}(\mathfrak {m})$, $\tilde {S}^{H}_{L_\beta }[\delta (x,y)]$ runs over the set of connected components of $\tilde {S}^{H}_{L_\beta }.$ Define the level $\beta$ evaluation:

(35)\begin{equation} \mathcal{E}^{j,\eta}_{\beta}= \sum_{[\bar x] \in \mathscr{C}\!\ell_F^{+}(p^{\beta})} \mathcal{E}^{j,\eta}_{\beta,[\bar x]}[\bar x],\quad \text{where } \mathcal{E}^{j,\eta}_{\beta,[\bar x]}=\sum_{[y] \in \mathscr{C}\!\ell_F^{+}(\mathfrak{m})} \sum_{[x]} \eta_0([y]) \mathcal{E}^{j,{{\sf w}}}_{\beta,[\delta( x,y)]}, \end{equation}

where the last sum runs over all $[x] \in \mathscr {C}\!\ell _F^{+}(p^{\beta }\mathfrak {m})$ mapping to $[\bar x]$ under the natural projection.

The following diagram recapitulates the steps in the construction of $\mathcal {E}^{j,\eta }_{\beta }$.

(36)

2.3 Distributions on $\mathscr {C}\!\ell _F^{+}(p^{\infty })$

The object of this section is to relate when $\beta$ varies the evaluation maps $\mathcal {E}^{j,\eta }_{\beta }$ whose definition is summarized in (36).

2.3.1 The distributive property

Fix a $\beta =(\beta _{\mathfrak {p}})_{\mathfrak {p}\mid p}$ with $\beta _{\mathfrak {p}}\in \mathbb {Z}_{>0}$ for all $\mathfrak {p}\mid p$.

Theorem 2.2 Given a prime $\mathfrak {p}\mid p$ we let $p^{\beta '}=p^{\beta }\mathfrak {p}$ and consider the canonical projection $\operatorname {pr}_{\beta ',\beta } : \mathscr {C}\!\ell _F^{+}(p^{\beta '}) \to \mathscr {C}\!\ell _F^{+}(p^{\beta })$. For all $[x] \in \mathscr {C}\!\ell _F^{+}(p^{\beta })$ we have $\mathcal {E}^{j,\eta }_{\beta }\circ U_\mathfrak {p}^{\circ }=\operatorname {pr}_{\beta ',\beta }\circ \mathcal {E}^{j,\eta }_{\beta '},$ that is,

\[ \mathcal{E}^{j,\eta}_{\beta,[x]}\circ U_\mathfrak{p}^{\circ} = \sum_{[x'] \in \operatorname{pr}_{\beta',\beta}^{-1}([x])} \mathcal{E}^{j,\eta}_{\beta',[x']}. \]

Proof. Using (33), (34), and (35) one has to show that for all $[x] \in \mathscr {C}\!\ell _F^{+}(p^{\beta }\mathfrak {m}), [y]\in \mathscr {C}\!\ell _F^{+}(\mathfrak {m})$:

\[ \mathcal{E}^{j,{{\sf w}}}_{\beta,\delta(x,y)}\circ U_\mathfrak{p}^{\circ} = \sum_{[x'] \in \operatorname{pr}_{\beta',\beta}^{-1}([x])} \operatorname{N}_{F_p/\mathbb{Q}_p}^{j}(u_{x'})\cdot \mathcal{E}^{j,{{\sf w}}}_{\beta',\delta(x',y)}, \]

where $u_{x'}\in I(p^{\beta })$ is such that $x'\in F^{\times } x u_{x'} F_\infty ^{\times \circ }$. We proceed as in the proof of [Reference Barrera, Dimitrov and JorzaBDJ, Proposition 3.4]. Pulling back the definition of the Hecke operator $U_\mathfrak {p}^{\circ }$ (see § 1.4) by the automorphic symbols (see § 2.2.1) and the twisting operators (see § 2.2.2) yields the following commutative diagram (we use implicitly that $p_{K^{0}(\mathfrak {p}),K}$ and $\operatorname {pr}_{\beta ',\beta }$ have the same degree as $L_{\beta }/L_{\beta '}\simeq M_n(\mathcal {O}/\mathfrak {p})$)

where the upper $[t_\mathfrak {p}]$ is induced by the morphism $(g,v)\mapsto (g\cdot t_\mathfrak {p}^{-1}, t_\mathfrak {p}\bullet v)$ of local systems, whereas the lower $[t_\mathfrak {p}]$ is induced by the morphism $(h,v)\mapsto (h, t_\mathfrak {p}\bullet v)$. Then

is another commutative diagram by (31), hence the claim.

2.3.2 Distributions for finite slope eigenvectors

Let $\phi \in \operatorname {H}^{t}_c({S^{G}_K}, \mathcal {V}_{\mathcal {O}}^{\mu })$ be an eigenvector for $U_{\mathfrak {p}}^{\circ }$ with eigenvalue $\alpha _\mathfrak {p}^{\circ }$ for all $\mathfrak {p}\mid p$. Then, for all $\beta =(\beta _\mathfrak {p})_{\mathfrak {p}\mid p}$, it is an eigenvector for $U_{p^{\beta }}^{\circ }$ with eigenvalue $\alpha _{p^{\beta }}^{\circ }=\prod _{\mathfrak {p}\mid p}(\alpha _\mathfrak {p}^{\circ })^{\beta _\mathfrak {p}}$. We say that $\phi$ is of finite slope if $\alpha _{p}^{\circ } \neq 0$ and in which case we define its slope as $v_p(\alpha _p^{\circ })$. A eigenvector $\phi$ of slope $0$ is called $Q$-ordinary. Being $Q$-ordinary is equivalent to saying that the $U_{\mathfrak {p}}$-eigenvalue $\alpha _\mathfrak {p}$ satisfies $|\alpha _\mathfrak {p}|_p = |\mu ^{\vee }(t_\mathfrak {p})|_p^{-1}$ for all $\mathfrak {p}\mid p$ (see § 4.2 for more details).

Given any $U_p$-eigenvector $\phi$ of finite slope and any $j\in \operatorname {Crit}(\mu )$ by Theorem 2.2 one has a well-defined element

(37)\begin{equation} \boldsymbol{\mu}^{j,\eta}_\phi=((\alpha_{p^{\beta}}^{\circ})^{-1} \mathcal{E}^{j,\eta}_{\beta}(\phi))_\beta, \end{equation}

which is thought of as an $E$-valued distribution on $\mathscr {C}\!\ell _F^{+}(p^{\infty })$.

We write $\operatorname {H}^{t}_c({S^{G}_K}, \mathcal {V}_{\mathcal {O}}^{\mu })^{Q-\mathrm {ord}}$ for the maximal $\mathcal {O}$-submodule of $\operatorname {H}^{t}_c({S^{G}_K}, \mathcal {V}_{\mathcal {O}}^{\mu })$ on which the operators $U_{\mathfrak {p}}^{\circ }$ are invertible for all $\mathfrak {p}\mid p$ (it is a direct $\mathcal {O}$-factor). Given any (not necessarily $U_p^{\circ }$-eigen) non-torsion element $\phi \in \operatorname {H}^{t}_c({S^{G}_K}, \mathcal {V}_{\mathcal {O}}^{\mu })^{Q-\mathrm {ord}}$ one defines

(38)\begin{equation} \boldsymbol{\mu}^{j,\eta}_\phi=(\mathcal{E}^{j,\eta}_{\beta}((U_{p^{\beta}}^{\circ})^{-1}(\phi)))_\beta \in \mathcal{O}[[\mathscr{C}\!\ell_F^{+}(p^{\infty})]]=\varprojlim_{\beta}\mathcal{O}[\mathscr{C}\!\ell_F^{+}(p^{\beta})], \end{equation}

which can be reinterpreted as a measure (i.e. a bounded distribution) on $\mathscr {C}\!\ell _F^{+}(p^{\infty })$.

2.4 Manin relations

Consider the $p$-adic cyclotomic character $\varepsilon : \mathscr {C}\!\ell _F^{+}(p^{\infty }) \to \mathbb {Z}_p^{\times }$ defined by composing the norm $\operatorname {N}_{F/\mathbb {Q}}: \mathscr {C}\!\ell _F^{+}(p^{\infty })\to \mathcal {C}\ell _\mathbb {Q}^{+}(p^{\infty })$ with the $p$-adic cyclotomic character over $\mathbb {Q}$. In this section, we prove the following result.

Theorem 2.3 Let $\mu \in X^{*}_0(T)$ and suppose that $j$ and $j+1$ both belong to $\operatorname {Crit}(\mu )$.

For $\phi \in \operatorname {H}^{t}_c({S^{G}_K}, \mathcal {V}_{\mathcal {O}}^{\mu })^{Q-\mathrm {ord}}$ the following equality holds in $\mathcal {O}[[\mathscr {C}\!\ell _F^{+}(p^{\infty })]]$:

\[ \varepsilon_{\operatorname{cyc}}(\boldsymbol{\mu}^{j,\eta}_\phi) = \boldsymbol{\mu}^{j+1,\eta}_\phi, \]

where $\varepsilon _{\operatorname {cyc}}$ denotes the automorphism of $\mathcal {O}[[\mathscr {C}\!\ell _F^{+}(p^{\infty })]]$ sending $[x]$ to $\varepsilon ([x])[x]$. Hence,

(39)\begin{equation} \boldsymbol{\mu}_\phi^{\eta}=\varepsilon_{\operatorname{cyc}}^{-j}(\boldsymbol{\mu}^{j,\eta}_\phi)\in \mathcal{O}[[\mathscr{C}\!\ell_F^{+}(p^{\infty})]], \end{equation}

is independent of $j\in \operatorname {Crit}(\mu )$.

The overdetermination of $\boldsymbol {\mu }^{\eta }_\phi$ in the $Q$-ordinary case, when there are at least two critical values, plays a pivotal role in the proof of main theorem. Before embarking on the proof of this theorem, we begin with some technical preparation (see [Reference JanuszewskiJan18, § 3]).

2.4.1 Lie theoretic considerations

By the distributive property (see Theorem 2.2) we may reduce to strict $p^{\beta }$-power level with integral exponents $\beta \in \mathbb {Z}_{>0},$ ignoring the finer components $\mathfrak {p}\mid p$ for simplicity of notation. Recall that ${{\mathfrak {b}}}={{\mathfrak {t}}}\oplus {{\mathfrak {n}}}$ and ${{\mathfrak {q}}}={{\mathfrak {h}}}\oplus {{\mathfrak {u}}}$. With the notation $t_p=\iota (p\textbf {1}_n,\textbf {1}_n)$, we observe for any $\beta \geqslant 0$ the relations

\[ t_p^{\beta}{{\mathfrak{n}}}_\mathcal{O} t_p^{-\beta}\subseteq {{\mathfrak{n}}}_\mathcal{O}, \quad t_p^{\beta}{{\mathfrak{u}}}_\mathcal{O} t_p^{-\beta}=p^{\beta}{{\mathfrak{u}}}_\mathcal{O}. \]

Recall the matrix $\xi = \big (\begin {smallmatrix} \textbf {1}_n & w_n\\ \textbf {0}_n & w_n \end {smallmatrix}\big ).$ A superscript ${}^{\xi }(-)$ denotes left conjugation action by $\xi$.

Proposition 2.4 We have the relations:

  1. (i) ${{\mathfrak {g}}}_\mathcal {O}={{\mathfrak {h}}}_\mathcal {O}+ {}^{\xi }\,{{\mathfrak {b}}}_\mathcal {O}^{-}$; and

  2. (ii) ${}^{\xi } \big ({{\mathfrak {n}}}_\mathcal {O}\cap {{\mathfrak {h}}}_\mathcal {O}\big ) \subseteq [{{\mathfrak {h}}},{{\mathfrak {h}}}]_\mathcal {O}+ {}^{\xi }\,{{\mathfrak {n}}}_\mathcal {O}^{-}$.

Proof. (i) As $\xi \in G(\mathcal {O})$, it suffices to verify it over $E$, where it amounts to show that $\dim _E({{\mathfrak {h}}}_E\cap {}^{\xi }\,{{\mathfrak {b}}}_E^{-}) = n$. To this end, let $l_1,l_2$ be lower triangular matrices in $M_n(E)$ and $u\in M_n(E)$. Then

\[ \xi\cdot \begin{pmatrix} l_1 & \\ u & l_2 \end{pmatrix}\cdot \xi^{-1} = \begin{pmatrix} l_1+w_nu & w_n l_2 w_n-l_1-w_nu\\ w_nu & w_n l_2 w_n-w_nu \end{pmatrix}, \]

lies in ${{\mathfrak {h}}}_E$ if and only if $u = 0$ and $l_1 = w_n l_2 w_n$. Therefore, $l_1$ and $l_2$ are diagonal matrices determining each other uniquely.

(ii) Conjugation by $\xi ^{-1}$ reduces the claim to the problem of solving

\[ \begin{pmatrix} n_1 & \\ & n_2 \end{pmatrix}= \begin{pmatrix} h_1 & (h_1-h_2)w_n\\ & w_n h_2 w_n \end{pmatrix} \;+\; \begin{pmatrix} \bar{n}_1 & \\ & \bar{n}_2 \end{pmatrix}, \]

for given $\iota (n_1,n_2)\in {{\mathfrak {h}}}\cap {{\mathfrak {n}}}_\mathcal {O}$ and unknowns $\iota (h_1,h_2)\in [{{\mathfrak {h}}}_\mathcal {O},{{\mathfrak {h}}}_\mathcal {O}]$ and $\iota (\bar {n}_1,\bar {n}_2)\in {{\mathfrak {n}}}^{-}$. The choice

\[ h_1=h_2=n_1+w_n n_2 w_n,\quad \bar{n}_1=-w_n n_2 w_n,\quad \bar{n}_2=-w_n n_1 w_n, \]

is a solution with the desired properties.

Corollary 2.5 For any $\beta \geqslant 0$, the following relations hold inside $\mathcal {U}({{\mathfrak {g}}}_\mathcal {O})$:

  1. (i) $\mathcal {U}({{\mathfrak {g}}}_\mathcal {O})= \mathcal {U}({{\mathfrak {h}}}_\mathcal {O}) \cdot \mathcal {U}({}^{\xi } {{\mathfrak {b}}}_\mathcal {O}^{-})$; and

  2. (ii) $\mathcal {U}({}^{\xi t_p^{\beta }}{{\mathfrak {n}}}_\mathcal {O})\subseteq \mathcal {U}([{{\mathfrak {h}}},{{\mathfrak {h}}}]_\mathcal {O}+p^{\beta }{{\mathfrak {h}}}_\mathcal {O})\cdot \mathcal {U}({}^{\xi }{{\mathfrak {n}}}_\mathcal {O}^{-} + p^{\beta } \, {}^{\xi }{{\mathfrak {b}}}_\mathcal {O}^{-})$.

Proof. (i) This is a consequence of Proposition 2.4(i) and the Poincaré–Birkhoff–Witt theorem.

(ii) The decomposition ${{\mathfrak {n}}}_\mathcal {O} = ({{\mathfrak {h}}}_\mathcal {O}\cap {{\mathfrak {n}}}_\mathcal {O})\oplus {{\mathfrak {u}}}_\mathcal {O},$ gives $t_p^{\beta }{{\mathfrak {n}}}_\mathcal {O} t_p^{-\beta } = ({{\mathfrak {h}}}_\mathcal {O}\cap {{\mathfrak {n}}}_\mathcal {O})\oplus p^{\beta }{{\mathfrak {u}}}_\mathcal {O}$. Conjugating by $\xi$, we obtain

\[ \xi t_p^{\beta}{{\mathfrak{n}}}_\mathcal{O} t_p^{-\beta}\xi^{-1}= {}^{\xi} \big({{\mathfrak{h}}}_\mathcal{O} \cap {{\mathfrak{n}}}_\mathcal{O} \big)\oplus p^{\beta} \, {}^{\xi}{{\mathfrak{u}}}_\mathcal{O}. \]

Applying Proposition 2.4(ii) to the first summand and Proposition 2.4(i) to the second we obtain

\[ \xi t_p^{\beta}{{\mathfrak{n}}}_\mathcal{O} t_p^{-\beta}\xi^{-1}\subseteq \big([{{\mathfrak{h}}},{{\mathfrak{h}}}]_\mathcal{O}+p^{\beta}{{\mathfrak{h}}}_\mathcal{O}\big)+ \big({}^{\xi}{{\mathfrak{n}}}_\mathcal{O}^{-} + p^{\beta} \, {}^{\xi} {{\mathfrak{b}}}_\mathcal{O}^{-} \big). \]

One concludes again by the Poincaré–Birkhoff–Witt theorem, because the sums within the parentheses on the right-hand side are Lie $\mathcal {O}$-algebras.

2.4.2 Lattices and the projection formula

Recall from (5) the lowest weight vector $v_0 \in V^{\mu }_{E}$ and the $G(\mathcal {O})$-lattice $V^{\mu }_{\mathcal {O}} = \mathcal {U}({{\mathfrak {g}}}_\mathcal {O})\cdot v_0 = \mathcal {U}({{\mathfrak {n}}}_\mathcal {O})\cdot v_0$. Recall also the $\bullet$-action of the semi-group $\Lambda _p$ on $V^{\mu }_{\mathcal {O}}$ as in (12).

Given $j \in \operatorname {Crit}(\mu )$ recall from § 2.2.3 the map $\kappa _j: V^{\mu }_{\mathcal {O}} \to V^{(j,{{\sf w}}-j)}_{\mathcal {O}}$. By Corollary 2.5(i)

\[ V^{\mu}_{\mathcal{O}}=\mathcal{U}({{\mathfrak{h}}}_\mathcal{O})\cdot \xi v_0, \]

which implies that $\kappa _j(\xi v_0)$ is an $\mathcal {O}$-basis of $V^{(j,{{\sf w}}-j)}_{\mathcal {O}}$ yielding a surjective $\mathcal {O}$-linear map

(40)\begin{equation} \kappa_j^{\circ} : V^{\mu}_{\mathcal{O}} \to \mathcal{O}, \quad \mbox{defined by } \kappa_j(v) = \kappa_j^{\circ}(v) \kappa_j(\xi v_0). \end{equation}

It is independent from the choice of $\kappa _j$ because of (28), and $\kappa _j^{\circ }(\xi v_0)=1$. We now come to the main technical result that is at the heart of our proof of the Manin relations.

Proposition 2.6 For any $\beta \geqslant 0$, $v\in (\xi t_p^{\beta })\bullet V^{\mu }_{\mathcal {O}} \subset V^{\mu }_{\mathcal {O}}$, and for all $j,j'\in \operatorname {Crit}(\mu )$, we have

(41)\begin{equation} \kappa^{\circ}_{j}(v) \equiv \kappa^{\circ}_{j'}(v)\pmod{p^{\beta}}. \end{equation}

Proof. By (12) for $v\in (\xi t_p^{\beta })\bullet V^{\mu }_{\mathcal {O}}$ there exists $m\in \mathcal {U}({{\mathfrak {n}}}_\mathcal {O})$ with

\[ v = \xi\cdot t_p^{\beta} \bullet (m v_0) = {}^{\xi t_p^{\beta}} m \cdot\xi (t_p^{\beta} \bullet v_0) = {}^{\xi t_p^{\beta}} m \cdot\xi v_0 \in \mathcal{U}({}^{\xi t_p^{\beta}}{{\mathfrak{n}}}_{\mathcal{O}}) \cdot\xi v_0. \]

By Corollary 2.5(ii) we can write

\[ {}^{\xi t_p^{\beta}} m = xy, \text{ with } x \in \mathcal{U}([{{\mathfrak{h}}},{{\mathfrak{h}}}]_\mathcal{O}+p^{\beta}{{\mathfrak{h}}}) \text{ and } y \in \mathcal{U}({}^{\xi}{{\mathfrak{n}}}_\mathcal{O}^{-}+p^{\beta}{}^{\xi}{{\mathfrak{b}}}_\mathcal{O}^{-}). \]

Let $x_0, y_0 \in \mathcal {O}$ be the degree zero terms of $x$ and $y$, respectively, and let

\begin{gather*} x_1 = x - x_0 \in ([{{\mathfrak{h}}},{{\mathfrak{h}}}]_\mathcal{O}+p^{\beta}{{\mathfrak{h}}})\cdot \mathcal{U}([{{\mathfrak{h}}},{{\mathfrak{h}}}]_\mathcal{O}+p^{\beta}{{\mathfrak{h}}}),\\ y_1 = y - y_0 \in ({}^{\xi}{{\mathfrak{n}}}_\mathcal{O}^{-}+p^{\beta}{}^{\xi}{{\mathfrak{b}}}_\mathcal{O}^{-})\cdot \mathcal{U}({}^{\xi}{{\mathfrak{n}}}_\mathcal{O}^{-}+p^{\beta}{}^{\xi}{{\mathfrak{b}}}_\mathcal{O}^{-}), \end{gather*}

be the higher degree terms in their respective enveloping algebras. Then

\begin{align*} \begin{aligned} \kappa_j^{\circ}(v)&= \kappa_j^{\circ}(xy \cdot \xi v_0) = x \cdot \kappa_j^{\circ}(y \cdot \xi v_0)\quad \mbox{(because $\kappa_j^{\circ}$ is $H$-equivariant)}\\ &\equiv x \cdot \kappa_j^{\circ}(y_0 \cdot \xi v_0)\pmod{p^{\beta}} \qquad\mbox{(because ${}^{\xi}{{\mathfrak{n}}}_\mathcal{O}^{-}$ acts trivially on $\xi v_0$)}\\ &\equiv x_0 \cdot\kappa_j^{\circ}(y_0\cdot\xi v_0)\pmod{p^{\beta}} \quad\,\,\,\mbox{(because $[{{\mathfrak{h}}},{{\mathfrak{h}}}]_\mathcal{O}$ acts trivially on a line)}\\ &= x_0y_0\cdot\kappa_j^{\circ}(\xi v_0) = x_0y_0,\end{aligned}\end{align*}

which does not depend on $j$ as claimed.

2.4.3 Proof of Theorem 2.3

As $\mathcal {O}[[\mathscr {C}\!\ell _F^{+}(p^{\infty })]]= \varprojlim _{\beta }(\mathcal {O}/p^{\beta }\mathcal {O})[\mathscr {C}\!\ell _F^{+}(p^{\beta })]$ and because $\varepsilon \pmod {p^{\beta }}$ factors through $\mathscr {C}\!\ell _F^{+}(p^{\beta })$, it is enough to check that given $\beta \geqslant 1$ and $[x]\in \mathscr {C}\!\ell _F^{+}(p^{\beta })$ one has

\[ \varepsilon ([x]) \mathcal{E}^{j,\eta}_{\beta,[x]}(\phi) \equiv \mathcal{E}^{j+1,\eta}_{\beta,[x]}(\phi) \pmod{p^{\beta}}. \]

As, by (32), one has $\operatorname {triv}_{[\delta (x,y)]}^{*}= \varepsilon (x^{j} y^{{{\sf w}}})\operatorname {triv}_{\delta (x,y)}^{*}$, it suffices to show that (see (36))

\[ \mathcal{E}^{j,\eta}_{\beta,\delta}(\phi)=(\!\cap \theta_{[\delta]}) \circ\operatorname{triv}_\delta^{*}\circ\kappa_j \circ \tau_\beta^{\circ}\circ \iota_\beta^{*}(\phi)\equiv (\!\cap \theta_{[\delta]}) \circ \operatorname{triv}_\delta^{*}\circ\kappa_{j+1}^{*} \circ \tau_\beta^{\circ}\circ \iota_\beta^{*}(\phi)\pmod{p^{\beta}}. \]

Now, by definition, the homomorphism of sheaves $\tau _\beta ^{\circ }$ defined in § 2.2.2 factors as

\[ \iota_\beta^{*}\mathcal{V}_{\mathcal{O}}^{\mu} \longrightarrow\iota^{*}\big((\xi t_p^{\beta})\bullet\mathcal{V}_{\mathcal{O}}^{\mu}\big) \longrightarrow \iota^{*}\mathcal{V}_{\mathcal{O}}^{\mu}. \]

Hence, Proposition 2.6 translates to the statement that (for the choice of basis of $V^{(j,{{\sf w}}-j)}_{\mathcal {O}}$ as in (40)) $(\!\cap \theta _{[\delta ]}) \circ \operatorname {triv}_\delta ^{*}\circ \kappa _j \circ \tau _\beta ^{\circ }\circ \iota _\beta ^{*}(\phi )\pmod {p^{\beta }}$ is independent of $j\in \operatorname {Crit}(\mu )$.

3. Local considerations

We delineate some local calculations that are needed in the global considerations of the next section. For only this section, $F$ denotes a finite extension of $\mathbb {Q}_p$, $\mathcal {O}$ its ring of integers, $\mathcal {P}$ the maximal ideal, $\varpi \in \mathcal {P}$ a uniformizer, $q=\#(\mathcal {O}/\mathcal {P})$, and $\delta$ the valuation of the different. We use local notation corresponding to the global notation introduced at the beginning of § 1. For example, $G=\operatorname {GL}_{2n}(F)\supset H=\operatorname {GL}_{n}(F)\times \operatorname {GL}_{n}(F)$.

3.1 Parahoric invariants

Let $K= \operatorname {GL}_{2n}(\mathcal {O})$ be the standard maximal compact subgroup of $G$. Define the parahoric (respectively, Iwahori) subgroup $J$ (respectively, $I$) of $K$ consisting of matrices whose reduction modulo $\mathcal {P}$ belongs to $Q(\mathcal {O}/\mathcal {P})$ (respectively, to $B(\mathcal {O}/\mathcal {P})$). One has

(42)\begin{equation} J = \bigg\{ \begin{pmatrix} a & b \\ c & d \end{pmatrix} \in K \ \bigg{|} \ a, d \in \operatorname{GL}_n(\mathcal{O}), c \in M_n(\mathcal{P}), b \in M_n(\mathcal{O}) \bigg\}. \end{equation}

Let $\Pi$ be an algebraic unramified and generic representation of $G$. Then there exists an unramified character $\lambda = \otimes _{i=1}^{2n} \lambda _i :T \to \bar {\mathbb {Q}}^{\times } \xrightarrow {i_\infty } \mathbb {C}^{\times }$ such that

(43)\begin{equation} \Pi= \operatorname{Ind}_{B}^{G}(|\cdot|^{({2n-1})/{2}}\lambda), \end{equation}

where the right-hand side is the normalized parabolic induction, which differs from the usual induction by $\delta _B^{{1}/{2}}$ where

\[ \delta_B(t_1,t_2,\ldots,t_{2n})= |t_1 |^{2n-1} |t_2 |^{2n-3} \cdot\cdots\cdot |t_{2n}|^{1-2n}. \]

Recall Jacquet's exact functor sending an admissible $G$-representation $V$ to the space of its co-invariants of $U$ defined as $V_U=V /\langle \{u\cdot v-v\mid u\in U, v\in V \} \rangle$, which is an admissible $H$-representation. The Weyl groups of $G\supset H$ are given by $\mathfrak {S}_{2n} \simeq W_G \supset W_H\simeq (\mathfrak {S}_{n}\times \mathfrak {S}_{n})$. The group $W_G$ acts on the right on characters of $T$. There is a natural bijection:

(44)\begin{equation} W_G / W_H\xrightarrow{\sim} \{\tau\subset \{1, 2, \ldots ,2n\} |\#\tau=n\},\,\ \rho\mapsto \{\rho(1), \ldots ,\rho(n)\}. \end{equation}

Lemma 3.1 The semi-simplification of the Jacquet module $\Pi _U$ is isomorphic to

(45)\begin{equation} \bigoplus_{ \tau\in W_G / W_H} \delta_Q^{{1}/{2}}\cdot \operatorname{Ind}_{B\cap H}^{H}(|\cdot|^{({2n-1})/{2}}\lambda^{\tau}), \end{equation}

where $\delta _Q(t_1,t_2,\ldots ,t_{2n})= |{t_1\ldots t_n}\cdot {t_{n+1}^{-1}\ldots t_{2n}^{-1}} |^{n}$. The semi-simplification can be omitted if $\Pi$ is regular in the sense that $\alpha _{i} = \lambda _i(\varpi )$ are pairwise distinct for $1\leqslant i\leqslant 2n$.

The characteristic polynomial of the Hecke operator $U_\mathcal {P}=[J t_\varpi J ]$ acting on $\Pi ^{J }$ equals

\[ \prod_{ \tau\in W_G / W_H}\bigg(X-q^{{n(1-n)}/{2}} \prod_{i\in \tau} \alpha_{i}\bigg). \]

Proof. The semi-simplification of the Jacquet module $\Pi _N$ with respect to $B$ is given by

(46)\begin{equation} \bigoplus_{ \rho\in W_G} \delta_B^{{1}/{2}}|\cdot|^{({2n-1})/{2}}\lambda^{\rho}. \end{equation}

As $\operatorname {Ind}_{B}^{G}= \operatorname {Ind}_{Q}^{G} \operatorname {Ind}_{B\cap H}^{H}$, Frobenius reciprocity implies that any irreducible sub-quotient of the Jacquet module of $\Pi$ with respect to $Q$ is isomorphic to one of the summands in (45). The first claim then follows by a simple dimension count based on (46) and the transitivity of the Jacquet functors. By Bruhat decomposition,

(47)\begin{equation} G=\coprod_{\rho \in W_G} B\rho I=\coprod_{\rho \in W_G/ W_H} B\rho J, \quad K=\coprod_{\rho \in W_G} (B\cap K) \rho I=\coprod_{\rho \in W_G/ W_H} (B\cap K) \rho J, \end{equation}

the dimension of $\Pi ^{J}$ is $\#(W_G/W_H)$. By the Iwasawa decomposition $H= (B\cap H)\cdot (H\cap J)$,

\[ \big(\operatorname{Ind}_{B\cap H}^{H}(\delta_Q^{{1}/{2}}|\cdot|^{({2n-1})/{2}}\lambda^{\tau})\big)^{H\cap J} \]

is a line on which the central element $\iota (\textbf {1}_{n},\varpi \textbf {1}_{n})$ acts by $q^{{n(1-n)}/{2}} \prod _{i\in \tau } \alpha _{i}$. Under the assumption that $\Pi$ is regular, the image of $\Pi ^{J }$ by the Jacquet functor equals the direct sum of the above lines when $\tau$ runs over $W_G / W_H$, hence the second claim. The proof of the third claim is a standard double coset computation based on (47) (see also [Reference HidaHid98]).

3.2 Twisted local Shalika integrals

We review the theory of global Shalika models and $L$-functions in § 4.1. The computations in this section are needed in § 4.3 to evaluate the twisted local zeta integral.

Fix an additive character $\psi :F\to \mathbb {C}^{\times }$ of conductor $\varpi ^{-\delta }$ and a multiplicative character $\eta : F^{\times } \to \mathbb {C}^{\times }$.

Definition 3.2 We say that an admissible representation $\Pi$ of $G$ has a local $(\eta ,\psi )$-Shalika model if there is a non-trivial (and, hence, injective) intertwining of $G=\operatorname {GL}_{2n}(F)$-modules

\[ \mathcal{S}^{\eta}_{\psi}:\Pi \hookrightarrow \operatorname{Ind}_{S}^{G}(\eta\otimes\psi). \]

For any $W\in \operatorname {Ind}_{S}^{G}(\eta \otimes \psi )$ and for any quasi-character $\chi :F^{\times } \to \mathbb {C}^{\times }$ the zeta integral

(48)\begin{equation} \zeta(s;W,\chi)=\int_{\operatorname{GL}_n(F)} W\bigg(\begin{pmatrix} h & 0\\ 0 & 1_n \end{pmatrix}\bigg) \chi(\det(h)) |\!\det(h)|^{s-{1}/{2}} \, d h \end{equation}

is absolutely convergent for $\Re (s)\gg 0$. The following result is due to Friedberg and Jacquet.

Proposition 3.3 [FJ93, Propositions 3.1 and 3.2] Assume that $\Pi$ has an $(\eta ,\psi )$-Shalika model. Then for each $W\in \mathcal {S}^{\eta }_{\psi }(\Pi )$, there is a holomorphic function $P(s;W,\chi )$ such that

\[ \zeta(s;W,\chi)=L(s,\Pi\otimes \chi)P(s;W,\chi). \]

One may analytically continue $\zeta (s;W,\chi )$ by re-defining it as $L(s,\Pi \otimes \chi )P(s;W,\chi )$ for all $s\in \mathbb {C}$. Moreover, there exists a vector $W_{\Pi }\in \mathcal {S}^{\eta }_{\psi }(\Pi )$ such that all unramified quasi-characters $\chi :F^{\times }\to \mathbb {C}^{\times }$ and every $s\in \mathbb {C}$ one has

\[ P(s;W_{\Pi},\chi)=(q^{s-{1}/{2}} \chi(\varpi))^{\delta n}. \]

If $\Pi$ is spherical, then $W_{\Pi }$ can be taken to be the spherical vector $W_{\Pi }^{\circ }\in \mathcal {S}^{\eta }_{\psi }(\Pi )$ normalized by the condition $W_{\Pi }^{\circ }(\mathbf {1}_{2n})=1$.

For ramified twists, we need the following refinement of Proposition 3.3.

Proposition 3.4 Let $W\in \mathcal {S}^{\eta }_{\psi }(\Pi )$ be a parahoric invariant vector, that is,

(49)\begin{equation} W \bigg(\begin{pmatrix} h & \\ & h \end{pmatrix} \begin{pmatrix} \mathbf{1}_n & X\\ & \mathbf{1}_n \end{pmatrix} g k \bigg)= \eta(\det h)\psi(\operatorname{tr} X)W(g), \end{equation}

for all $h\in \operatorname {GL}_n(F),$ $X\in M_n(F),$ $g\in G$ and $k\in J$. Then for every finite order character $\chi :F^{\times }\to \mathbb {C}^{\times }$ of conductor $\beta \geqslant 1$, and for all $s\in \mathbb {C}$ with $\Re (s)\gg 0$ one has

\[ \zeta(s;W(-\cdot \xi t_\varpi^{\beta}),\chi) = \mathcal{G}(\chi)^{n} \cdot q^{\beta n(1-n)+(\beta+\delta) n(s-{1}/{2})} W(t_\varpi^{-\delta}). \]

Proof. For any $h\in \operatorname {GL}_{n}(F)$ and $X\in M_n(\mathcal {O})$, the Shalika property (49) implies that

\[ W\bigg(\begin{pmatrix}h & \\ & \textbf{1}\end{pmatrix}\xi t_\varpi^{\beta}\bigg) = W\bigg(\begin{pmatrix}h & \\ & \textbf{1}\end{pmatrix}\xi t_\varpi^{\beta}\begin{pmatrix}\textbf{1} & X\\ & \textbf{1}\end{pmatrix}\bigg) = \psi(\operatorname{tr} (h \varpi^{\beta} X w_n))\cdot W\bigg( \begin{pmatrix}h & \\ & \textbf{1}\end{pmatrix} \xi t_\varpi^{\beta}\bigg), \]

hence, the zeta integral is supported over $\operatorname {GL}_n(F)\cap \varpi ^{-\beta -\delta }M_n(\mathcal {O})$. In addition, for $h\in \operatorname {GL}_{n}(F)$:

\[ W\bigg(\begin{pmatrix}h & \\ & \textbf{1}\end{pmatrix}\xi t_\varpi^{\beta}\bigg) = W\bigg(\begin{pmatrix}\textbf{1}_n & h\\ & \textbf{1}_n\end{pmatrix} \begin{pmatrix}h & \\ & w_n\end{pmatrix} t_\varpi^{\beta}\bigg) = \psi(\operatorname{tr} h)\cdot W\bigg(\begin{pmatrix}h \varpi^{\beta} & \\ & \textbf{1}_n \end{pmatrix} \bigg). \]

Using this and changing the variable $h\mapsto h \varpi ^{-\beta '}$ with $\beta '=\beta +\delta$ yields

(50)\begin{align*} &\zeta(s; W(-\cdot \xi t_\varpi^{\beta}),\chi)\\ &\qquad= \int_{\operatorname{GL}_n(F)\cap M_n(\mathcal{O})} W\bigg(\begin{pmatrix}h\varpi^{-\delta} & \\ & \textbf{1}_n\end{pmatrix}\bigg) \psi(\operatorname{tr} (h\varpi^{-\beta'})) (\chi|\cdot|^{s-{1}/{2}})(\det (h\varpi^{-\beta'})) \, {d} h. \end{align*}

Denote by $(e_{ij})_{1\leqslant i,j\leqslant n}$ the standard basis of $M_n(\mathcal {O})$. As $W$ is parahoric invariant, for any $i\neq j$ and $c\in \mathcal {O}$, right translation by $\textbf {1}_{n}+c e_{ij}\in \operatorname {SL}_n(\mathcal {O})$ in (50) yields

\begin{align*} &\zeta(s; W(-\cdot \xi t_\varpi^{\beta}),\chi)\\ &\qquad = \int dh\, W\bigg(\begin{pmatrix}h\varpi^{-\delta} & \\ & \textbf{1}_n\end{pmatrix}\bigg) \psi(\operatorname{tr} (h\varpi^{-\beta'})) (\chi|\cdot|^{s-{1}/{2}})(\det (h\varpi^{-\beta'})) \int_{\mathcal{O}} d c\, \psi(c h_{ji}\varpi^{-\beta'}), \end{align*}

and observe that $\int _{\mathcal {O}} \psi (c h_{ji}\varpi ^{-\beta '})\,dc=0$ unless $h_{ji}\in \mathcal {P}^{\beta }$.

Similarly, right translation by $\textbf {1}_{n}+ (c-1)e_{ii}$ with $c\in \mathcal {O}^{\times }$ shows that (50) equals

\[ \int W\bigg(\begin{pmatrix}h & \\ & \textbf{1}_n\end{pmatrix}\bigg) \psi((\operatorname{tr} (h)-h_{ii})\varpi^{-\beta'}) (\chi|\cdot|^{s-{1}/{2}})(\det (h\varpi^{-\beta'})) \bigg(\int_{\mathcal{O}^{\times}} \psi(c h_{ii} \varpi^{-\beta'}) \chi(c)d^{\times} c \bigg) \, d h, \]

and $\int _{\mathcal {O}^{\times }} \psi (c h_{ii} \varpi ^{-\beta '}) \chi (c)\,d^{\times } c =0$ unless $h_{ii}\in \mathcal {O}^{\times }$ as $\beta \geqslant 1$ equals the conductor of $\chi$.

Therefore, one can further restrict the domain of integration in (50) to the congruence subgroup $\ker (\operatorname {GL}_n(\mathcal {O})\to \operatorname {GL}_n(\mathcal {O}/\mathcal {P}^{\beta }))\cdot T_n(\mathcal {O}),$ which, by the Iwahori decomposition, may be identified to the product $N^{-}_n(\mathcal {P}^{\beta })\times T_n(\mathcal {O})\times N_n(\mathcal {P}^{\beta })$, where $T_n$ denotes the diagonal subgroup of $\operatorname {GL}_n$ and $N_n$ denotes the unipotent radical of the standard Borel subgroup $B_n$. Hence,

\[ \zeta(s; W(-\cdot \xi t_\varpi^{\beta}),\chi) = q^{\beta' n(s-{1}/{2})} W(t_\varpi^{-\delta}) \int_{N^{-}_n(\mathcal{P}^{\beta})T_n(\mathcal{O})N_n(\mathcal{P}^{\beta})} \psi(\operatorname{tr} (k\varpi^{-\beta'})) \chi(\det (k\varpi^{-\beta'}))\, dk, \]

which can be simplified as

\begin{align*} &q^{\beta n(1-n)+\beta' n(s-{1}/{2})} W(t_\varpi^{-\delta})\prod_{1\leqslant i\leqslant n} \int_{\mathcal{O}^{\times}} \psi(t_i \varpi^{-\beta'}) \chi(t_i \varpi^{-\beta'})\,d^{\times} t_i \\ &\quad = q^{\beta n(1-n)+(\beta+\delta) n(s-{1}/{2})} W(t_\varpi^{-\delta})\cdot \mathcal{G}(\chi)^{n}, \end{align*}

as desired.

3.3 Non-vanishing of a local twisted zeta integral

In order to ensure the non-vanishing of the local twisted Shalika integral in Proposition 3.4, which is crucial for our applications, one has to exhibit a parahoric-spherical Shalika function $W$ on $G$ such that $W(t_\varpi ^{-\delta }) \neq 0$. Assume that $\Pi$ is a spherical representation isomorphic to $\operatorname {Ind}_{B}^{G}(|\cdot |^{({2n-1})/{2}} \lambda )$ as in (43) and let $\alpha _{i}=\lambda _i(\varpi )$, $1\leqslant i\leqslant 2n$. Consider an unramified character $\eta$ of $F^{\times }$.

Definition 3.5 Let $\tau \in W_G/W_H$ thought of as an $n$-element subset of $\{1,\ldots , 2n\}$ (see (44)). We say that $\tilde \Pi =(\Pi , \tau )$ is $Q$-regular if it satisfies the following two conditions:

  1. (i) $q^{{n(1-n)}/{2}} \prod _{i\in \tau } \alpha _{i}$ is a simple eigenvalue for $U_\mathcal {P}=[J t_\varpi J ]$ acting on $\Pi ^{J }$;

  2. (ii) there exists $\rho \in \mathfrak {S}_{2n}$ such that for all $i\in \tau ,$ $\rho (i)\notin \tau$ and $\alpha _{i} \alpha _{\rho (i)} = q^{2n-1} \eta (\varpi ).$

Assume that $\tilde \Pi =(\Pi , \tau )$ is $Q$-regular. Then condition (i) together with Lemma 3.1 implies

(51)\begin{equation} \prod_{i\in \tau, j\notin \tau} ( \alpha_{i} - \alpha_{j})\neq 0, \end{equation}

whereas condition (ii) implies by [Reference Ash and GinzburgAG94, Proposition 1.3] that $\Pi$ admits a $(\eta ,\psi )$-Shalika model.

Without loss of generality assume from now on that $\tau =\{n+1,\ldots ,2n\}$ and that $\rho \in \mathfrak {S}_{2n}$ is the order $2$ element such that $\rho (i)=n+i$ for all $1\leqslant i\leqslant n$. In [Reference Ash and GinzburgAG94, (1.3)] the authors construct an $(\eta , \psi )$-Shalika functional on $\Pi$ sending $f\in \operatorname {Ind}_{B_{2n}}^{\operatorname {GL}_{2n}}(|\cdot |^{({2n-1})/{2}} \lambda )$ to

(52)\begin{equation} \mathcal{S}(f)(g) = \int_{B_n \backslash \operatorname{GL}_n} \int_{M_n} f\bigg(\begin{pmatrix} & \textbf{1}_n \\ \textbf{1}_n & X \end{pmatrix} \begin{pmatrix} h & \\ & h \end{pmatrix} g \bigg) \eta^{-1}(\det(h)) \bar\psi({\rm tr}(X)) \, dX\, dh. \end{equation}

By [Reference Ash and GinzburgAG94, Lemma 1.5], this integral converges in a certain domain and, when multiplied by (51), can be analytically continued to $\mathbb {C}^{2n}$, thus makes sense whenever (51) is non-zero. Let $f_0 \in \operatorname {Ind}_{B}^{G}(|\cdot |^{({2n-1})/{2}} \lambda )$ be the unique parahoric-spherical function supported on $B w_{2n} J$ and characterized by $f_0\big ( \big (\begin {smallmatrix} \textbf {1}_n & \\ & \varpi ^{-\delta }\textbf {1}_n \end {smallmatrix}\big ) w_{2n}\big ) = q^{-\delta n^{2}}$. The following analogue of [Reference Ash and GinzburgAG94, Lemma 1.4] holds.

Lemma 3.6 Let $W=\mathcal {S}(f_0)$. Then $W(t_\varpi ^{-\delta }) =1$. Moreover, $U_\mathcal {P}\cdot f_0= q^{{n(1-n)}/{2}}(\prod _{i=n+1}^{2n} \alpha _i) f_0$.

Proof. By the Iwasawa decomposition $\operatorname {GL}_n = B_n K_n$ and as $\iota (K_n,K_n) \subset J$ we see that

\begin{align*} W(t_\varpi^{-\delta}) = \mathcal{S}(f_0)(t_\varpi^{-\delta}) & = \int_{M_n} f_0\bigg(\begin{pmatrix} & \textbf{1}_n \\ \textbf{1}_n & X \end{pmatrix} t_\varpi^{-\delta} \bigg) \bar\psi({\rm tr}(X)) \, dX \\ & = \int_{M_n} f_0\bigg( \begin{pmatrix} \textbf{1}_n & \\ & \varpi^{-\delta}\textbf{1}_n \end{pmatrix} \bigg( \begin{pmatrix} & \textbf{1}_n \\ \textbf{1}_n & \varpi^{\delta}X \end{pmatrix} \bigg) \bar\psi({\rm tr}(X)) \, dX \\ & = f_0 \bigg(\begin{pmatrix} \textbf{1}_n & \\ & \varpi^{-\delta}\textbf{1}_n \end{pmatrix} w_{2n}\bigg) q^{\delta n^{2}}\!\int_{M_n} \! f_0\bigg( \begin{pmatrix} & \textbf{1}_n \\ \textbf{1}_n & X \end{pmatrix} \bigg) \bar\psi({\rm tr}(\varpi^{-\delta}X)) \, dX=1. \end{align*}

One checks that $\big ( \begin {smallmatrix} & \textbf {1}_n \\ \textbf {1}_n & X \end {smallmatrix} \big ) \in Bw_{2n} J$ if and only if $X \in M_n(\mathcal {O})$, in which case $\psi ({\rm tr}(\varpi ^{-\delta }X))=1$. The parahoric decomposition of $J=(J\cap U^{-})(J \cap Q)=(J \cap U^{-})(J \cap Q)$ implies

(53)\begin{equation} J t_\varpi J=\bigsqcup_{m\in M_n(\mathcal{O}/\mathcal{P})} \begin{pmatrix} \textbf{1}_n & m \\ & \textbf{1}_n \end{pmatrix} t_\varpi J. \end{equation}

By (47) it suffices to compute $(U_\mathcal {P}\cdot f_0)(\rho )$ for all $\rho \in W_G$. By the previous decomposition,

\[ (U_\mathcal{P}\cdot f_0)(\rho)=\sum_{m\in M_n(\mathcal{O})/M_n(\mathcal{P})} f_0\bigg(\rho \begin{pmatrix} \varpi\textbf{1}_n & m \\ & \textbf{1}_n \end{pmatrix}\bigg). \]

Note that $\rho \big (\begin {smallmatrix} \textbf {1}_n & m \\ & \textbf {1}_n \end {smallmatrix} \big )t_\varpi$ belongs to the support $B w_{2n} J = B w_{2n} t_\varpi J = B w_{2n} J^{-} t_\varpi$ of $f_0$ if and only if $\rho \big (\begin {smallmatrix} \textbf {1}_n & m \\ & \textbf {1}_n \end {smallmatrix} \big )\in K\cap B w_{2n} J^{-} = (K\cap B) w_{2n} J^{-}=w_{2n} J^{-}$ (see (47)), which implies $\rho =w_{2n}$ and $m\in M_n(\mathcal {P})$. Hence, $(U_\mathcal {P}\cdot f_0)(\rho )=0$ for all $\rho \neq w_{2n}$, while $(U_\mathcal {P}\cdot f_0)(w_{2n})=f_0\big (w_{2n} \big (\begin {smallmatrix} \varpi \textbf {1}_n & \\ & \textbf {1}_n \end {smallmatrix} \big )\big ) =f_0\big (\big (\begin {smallmatrix} \textbf {1}_n & \\ & \varpi \textbf {1}_n \end {smallmatrix} \big )w_{2n} \big )= q^{{n(1-n)}/{2}}(\prod _{i=n+1}^{2n} \alpha _i) f_0(w_{2n})$.

4. $L$-functions for $\operatorname {GL}_{2n}$

4.1 Global Shalika models and periods

This subsection contains a brief review of the necessary ingredients from [Reference Grobner and RaghuramGR14] and a discussion involving $p$-adically integrally refined Betti–Shalika periods. Henceforth, $\Pi$ denotes a (not necessarily unitary) cuspidal automorphic representation of $G(\mathbb {A}) = \operatorname {GL}_{2n}(\mathbb {A}_F)$. Keeping multiplicity one for $\operatorname {GL}_{2n}$ in mind, we let $\Pi$ also denote its representation space within the space of cusp forms for $G(\mathbb {A})$. Fix the non-trivial additive unitary character $\psi : \mathbb {A}_{F}/F\longrightarrow \mathbb {A}/\mathbb {Q} \longrightarrow \mathbb {C}^{\times }$ where the first map is the trace, whereas the second is the usual additive character $\psi _0$ on $\mathbb {A}/\mathbb {Q}$ characterized by $\ker (\psi _0|_{\mathbb {Q}_\ell })=\mathbb {Z}_\ell$ for every prime number $\ell$ and $\psi _0|_{\mathbb {R}}(x)=\exp (2\pi ix)$. We remark that $(\varpi _{v}^{-\delta _v})$, where $\delta _v$ is the valuation at $v$ of the different $\mathfrak {d}$ of $F$, is the largest ideal contained in $\ker (\psi _v)$. The discriminant of $F$ is $\operatorname {N}_{F/\mathbb {Q}}(\mathfrak {d})$.

4.1.1 Global Shalika models

Let $\eta : F^{\times } \backslash \mathbb {A}_F^{\times } \to \mathbb {C}^{\times }$ be a Hecke character such that $\eta ^{n}$ equals the central character $\omega _\Pi$ of $\Pi$. We obtain an automorphic character:

\[ \eta \otimes \psi: S(F) \backslash S(\mathbb{A}_F)\to \mathbb{C}^{\times}, \quad \begin{pmatrix} h & hX\\ 0 & h \end{pmatrix}\mapsto \eta(\det(h))\psi(Tr(X)). \]

For a cusp form $\varphi \in \Pi$ and $g\in G(\mathbb {A})$ consider the integral

(54)\begin{equation} W^{\eta}_{\varphi}(g)=\int_{Z(\mathbb{A})S(F)\backslash S(\mathbb{A}_F)} \varphi(sg)(\eta \otimes \psi)^{-1}(s) \, d s, \end{equation}

where Haar measures are normalized as in [Reference Grobner and RaghuramGR14, § 2.8]. It is well-defined by the cuspidality of the function $\varphi$ (see [Reference Jacquet and ShalikaJS90, § 8.1]) and, hence, yields a function $W^{\eta }_{\varphi }: G(\mathbb {A})\rightarrow \mathbb {C}$ such that

\[ W^{\eta}_{\varphi}(sg) = (\eta\otimes\psi)(s)\cdot W^{\eta}_{\varphi}(g), \]

for all $g\in G(\mathbb {A})$ and $s\in S(\mathbb {A})$. In particular, we obtain an intertwining of $G(\mathbb {A})$-modules

(55)\begin{equation} \mathcal{S}^{\eta}_\psi: \Pi\rightarrow {\rm Ind}_{S(\mathbb{A})}^{G(\mathbb{A})}(\eta\otimes\psi), \quad \varphi\mapsto W^{\eta}_{\varphi}. \end{equation}

The following theorem, due to Jacquet and Shalika, gives a necessary and sufficient conditions for the existence of a non-zero intertwining as in (55).

Theorem 4.1 [JS90, Theorem 1] The following assertions are equivalent.

  1. (i) There exists $\varphi \in \Pi$ such that $W^{\eta }_{\varphi } \neq 0$.

  2. (ii) There exists an injection of $G(\mathbb {A})$-modules $\Pi \hookrightarrow {\rm {Ind}}_{S(\mathbb {A})}^{G(\mathbb {A})}(\eta \otimes \psi )$.

  3. (iii) The twisted partial exterior square $L$-function $\prod _{v\notin \Sigma _\Pi } L(s, \Pi _v, \wedge ^{2} \otimes \eta ^{-1}_v)$ has a pole at $s=1$, where $\Sigma _\Pi$ is the set of places where $\Pi$ is ramified.

This is proved in [Reference Jacquet and ShalikaJS90] for unitary representations and its extension to the non-unitary case is easy. If $\Pi$ satisfies any one, and hence all, of the equivalent conditions of Theorem 4.1, then we say that $\Pi$ has an $(\eta ,\psi )$-Shalika model, and we call the isomorphic image $\mathcal {S}^{\eta }_\psi (\Pi )$ of $\Pi$ under (55) a global $(\eta ,\psi )$-Shalika model of $\Pi$. Then clearly $\Pi \otimes \chi$ has an $(\eta \chi ^{2},\psi )$-Shalika model for any Hecke character $\chi$, by keeping the same model and only twisting the action.

The following proposition (see [Reference Asgari and ShahidiAS14]) gives another equivalent condition for $\Pi$ to have a global Shalika model.

Proposition 4.2 Let $\Pi$ be a cuspidal automorphic representation of $\operatorname {GL}_{2n}(\mathbb {A}_F)$ with central character $\omega _\Pi$. Then the following assertions are equivalent:

  1. (i) $\Pi$ has a global $(\eta ,\psi )$-Shalika model for some character $\eta$ satisfying $\eta ^{n}=\omega _\Pi$;

  2. (ii) $\Pi$ is the transfer of a globally generic cuspidal automorphic representation $\pi$ of ${\rm GSpin}_{2n+1}(\mathbb {A}_F)$.

In particular, if any of these equivalent conditions is satisfied, then $\Pi$ is essentially self-dual, that is, $\Pi \cong \Pi ^{\vee }\otimes \eta$. The character $\eta$ may be taken to be the central character of $\pi$.

4.1.2 Period integrals and $L$-functions

The following proposition, due to Friedberg and Jacquet, is crucial for much that follows. It relates the period integral over $H$ of a cusp form $\varphi$ of $G$ to a certain zeta integral of the function $W^{\eta }_{\varphi }$ in the Shalika model corresponding to $\varphi$ over one copy of $\operatorname {GL}_n$.

Proposition 4.3 [FJ93, Proposition 2.3] Assume that $\Pi$ has an $(\eta ,\psi )$-Shalika model. For $\varphi \in \Pi$,

\[ \Psi(s,\varphi,\chi,\eta)= \int_{Z(\mathbb{A})H(\mathbb{Q})\backslash H(\mathbb{A})} \varphi\bigg(\begin{pmatrix} h_1 & 0\\ 0 & h_2 \end{pmatrix}\bigg)(\chi | \cdot|^{s-{1}/{2}})\bigg(\frac{\det(h_1)}{\det(h_2)}\bigg)\eta^{-1}(\det(h_2)) \, d h_1 \,d h_2 \]

converges absolutely for all $s\in \mathbb {C}$. For $\Re (s)\gg 0$ it is equal to

\[ \zeta(s;W^{\eta}_{\varphi},\chi)=\int_{\operatorname{GL}_n(\mathbb{A}_F)} W^{\eta}_{\varphi}\bigg(\begin{pmatrix}h & 0\\0 & 1 \end{pmatrix}\bigg) \chi(\det(h)) |\!\det(h)|^{s-{1}/{2}} \, dh, \]

thus providing an analytic continuation of $\zeta (s;W^{\eta }_{\varphi },\chi )$ to all of $\mathbb {C}$.

Suppose the representation $\Pi$ of $G(\mathbb {A}) = \operatorname {GL}_{2n}(\mathbb {A}_F)$ decomposes as $\Pi = \otimes '_v \Pi _v$, where $\Pi _v$ is an irreducible admissible representation of $\operatorname {GL}_{2n}(F_v)$.

If $\Pi$ has a global Shalika model, then $\mathcal {S}^{\eta }_\psi$ defines local Shalika models at every place (see Definition 3.2). The corresponding local intertwining operators are denoted by $\mathcal {S}^{\eta _v}_{\psi _v}$ and their images by $\mathcal {S}^{\eta _v}_{\psi _v}(\Pi _v)$, whence $\mathcal {S}^{\eta }_\psi (\Pi )=\otimes '_v \mathcal {S}^{\eta _v}_{\psi _v}(\Pi _v)$. We can now consider cusp forms $\varphi$ such that the function $W_{\varphi }\in \mathcal {S}^{\eta }_\psi (\Pi )$ is factorizable as $W_\varphi =\otimes '_v W_{\varphi _v},$ where

\[ W_{\varphi_v}\in \mathcal{S}^{\eta_v}_{\psi_v}(\Pi_v)\subset {\rm Ind}_{S(F_v)}^{\operatorname{GL}_{2n}(F_v)}(\eta_v\otimes\psi_v). \]

Then the following factorization holds for $\Re (s) \gg 0$:

(56)\begin{equation} \zeta(s;W_{\varphi},\chi)=\prod_{v } \zeta_v(s;W_{\varphi_v},\chi_v), \end{equation}

where the non-Archimedean local zeta integrals $\zeta _v(s;W_{\varphi _v},\chi _v)$ are related to $L$-functions in Proposition 3.3.

Proposition 4.3 relates this Shalika zeta integral to a period integral over $H$, and the main thrust of [Reference Ash and GinzburgAG94], refined and generalized in [Reference Grobner and RaghuramGR14], is that the period integral over $H$ admits a cohomological interpretation, provided that $\Pi$ is of cohomological type.

4.1.3 Shalika models and cuspidal cohomology

In this section, we recall some well-known facts from Clozel [Reference ClozelClo90, § 3] (see also [Reference Grobner and RaghuramGR14, § 3.4]). Assume from now on that the cuspidal automorphic representation $\Pi$ is cohomological with respect to a dominant integral weight $\mu \in X_+^{*}(T)$ (see (3)), that is,

\[ \operatorname{H}^{q}({{\mathfrak{g}}}_\infty,K_\infty^{\circ} ;\Pi\otimes V^{\mu}_{\mathbb{C}}) = \operatorname{H}^{q}({{\mathfrak{g}}}_\infty,K_\infty^{\circ} ;\Pi_\infty\otimes V^{\mu}_{\mathbb{C}})\otimes\Pi_f \neq 0 \]

for some degree $q$. A necessary condition for the non-vanishing of this cohomology group is that the weight $\mu$ is pure, that is, $\mu \in X_0^{*}(T)$. For each archimedean place $\sigma \in \Sigma _{\infty }$, $\Pi _\sigma$ can be described explicitly as follows. For any integer $\ell \geqslant 1$ consider the unitary discrete series representation $D(\ell )$ of $\operatorname {GL}_2(\mathbb {R})$ of lowest non-negative ${\rm SO}_2$-type $\ell +1$ and central character $\mathrm {sgn}^{\ell +1}$. Let $P$ be the parabolic subgroup of $\operatorname {GL}_{2n}$ with Levi factor $\prod _{i=1}^{n} \operatorname {GL}_2$. Then

\[ \Pi_\sigma\simeq{\rm Ind}^{\operatorname{GL}_{2n}(\mathbb{R})}_{P(\mathbb{R})} \bigg(\bigotimes_{i=1}^{n} D(2(\mu_{\sigma,i}+n-i)+ 1-{{\sf w}})\otimes |\!\det\!|^{-{{\sf w}}/2}\bigg), \]

in particular $\omega _{\Pi _\sigma }=|\cdot |^{-n {{\sf w}}}$. The highest degree supporting cuspidal cohomology of $G$ is $t=|\Sigma _\infty |(n^{2}+n-1)$. For any character $\epsilon$ of $K_{\infty }/K_\infty ^{\circ }$ the $\epsilon$-eigenspace of

(57)\begin{equation} \operatorname{H}^{t}({{\mathfrak{g}}}_\infty,K_\infty^{\circ} ; \Pi_\infty \otimes V^{\mu}_{\mathbb{C}}) = \operatorname{Hom}_{K_\infty^{\circ} } \big(\wedge^{t}({{\mathfrak{g}}}_\infty/{{\mathfrak{k}}}_\infty), \Pi_\infty \otimes V^{\mu}_{\mathbb{C}}\big), \end{equation}

is a line. If, in addition, $\Pi$ admits an $(\eta ,\psi )$-Shalika model, then $\eta$ is forced to be algebraic of the form $\eta = \eta _0 | \cdot |_F^{-{{\sf w}}}$ with $\eta _0$ of finite order, ${{\sf w}}$ is the purity weight of $\mu$ (see [Reference Gan and RaghuramGR13, Theorem 5.3]). Using the multiplicity one theorem for local Shalika models [Reference NienNie09] (see also [Reference Chen and SunCS20]), one deduces that, for any character $\epsilon$ of $K_{\infty }/K_\infty ^{\circ }$,

\[ \operatorname{H}^{t}({{\mathfrak{g}}}_\infty,K_{\infty}^{\circ} ;\mathcal{S}^{\eta_\infty}_{\psi_\infty}(\Pi_\infty)\otimes V^{\mu}_{\mathbb{C}})[\epsilon], \]

is a line, a basis $\Xi _\infty ^{\epsilon }$ of which we fix in way compatible with twisting (see [Reference Grobner and RaghuramGR14, Lemma 5.1.1]). The relative Lie algebra cohomology of $\Pi$ as previously is a summand of the cuspidal cohomology, which, in turn, injects into the cohomology with compact supports (see [Reference Gan and RaghuramGR13, § 2])

(58)\begin{equation} \operatorname{H}^{t}({{\mathfrak{g}}}_\infty,K_{\infty}^{\circ} ;\Pi^{K}\otimes V^{\mu}_{\mathbb{C}}) \ \hookrightarrow \ \operatorname{H}^{t}_{\rm cusp}({S^{G}_K}, \mathcal{V}_{\mathbb{C}}^{\mu}) \ \hookrightarrow \ \operatorname{H}^{t}_c({S^{G}_K}, \mathcal{V}_{\mathbb{C}}^{\mu}). \end{equation}

We define an isomorphism $\Theta ^{\epsilon }$ of $G(\mathbb {A}_f)$-modules as the composition

(59)\begin{align} \mathcal{S}^{\eta_f}_{\psi_f}(\Pi_f) &\xrightarrow{\sim} \mathcal{S}^{\eta_f}_{\psi_f}(\Pi_f) \otimes \operatorname{H}^{t}({{\mathfrak{g}}}_\infty,K_{\infty}^{\circ} ; \mathcal{S}^{\eta_{\infty}}_{\psi_{\infty}}(\Pi_\infty) \otimes V^{\mu}_{\mathbb{C}})[\epsilon] \nonumber\\ &\xrightarrow{\sim} \operatorname{H}^{t}({{\mathfrak{g}}}_\infty,K_{\infty}^{\circ} ; \mathcal{S}^{\eta}_{\psi}(\Pi) \otimes V^{\mu}_{\mathbb{C}})[\epsilon] \xrightarrow{\sim} \operatorname{H}^{t}({{\mathfrak{g}}}_\infty,K_{\infty}^{\circ} ; \Pi \otimes V^{\mu}_{\mathbb{C}})[\epsilon], \end{align}

where the first map is $W_f \mapsto W_f \otimes \Xi _\infty ^{\epsilon }$, the second map is the natural one and the third map is the map induced in cohomology by $(\mathcal {S}^{\eta }_\psi )^{-1}$ from (55). Taking $K$-invariants in (59) and composing with (58) yields a Hecke equivariant embedding

(60)\begin{equation} \Theta^{\epsilon}_K: \mathcal{S}^{\eta_f}_{\psi_f}(\Pi_f)^{K} \hookrightarrow \operatorname{H}^{t}_c({S^{G}_K}, \mathcal{V}_{\mathbb{C}}^{\mu})[\epsilon]. \end{equation}

The reader should appreciate that the analytic condition on $\Pi$ of admitting a Shalika model and the algebraic condition of contributing to the cuspidal cohomology of $G$ are of an entirely different nature. One may construct examples of representations satisfying only one of these conditions and not the other (see [Reference Grobner and RaghuramGR14, § 3.5]).

4.2 Ordinarity and regularity

For $\mathfrak {p}$ dividing $p$, we let $\varpi _\mathfrak {p}$ denote a uniformizer of $F_\mathfrak {p}$ and let $q_\mathfrak {p}=|\varpi _\mathfrak {p} |_p^{-1}$ denote the cardinality of its residue field. Let $\Sigma _\infty =\coprod _{\mathfrak {p}\mid p} \Sigma _\mathfrak {p}$ be the partition induced by $i_p:\bar{\mathbb {Q}}\hookrightarrow \bar{\mathbb {Q}}_p$, where $\Sigma _\mathfrak {p}=\{\sigma :F_\mathfrak {p}\hookrightarrow \bar{\mathbb {Q}}_p\}$.

Recall from § 1.1 that a weight $\mu \in X^{*}_+(T)$ yields a rational character $\mu :T=\operatorname {Res}_{F/\mathbb {Q}}T_{2n}\to \operatorname {GL}_1$, therefore induces a character $\mu _p=\otimes _{\mathfrak {p}\mid p}\mu _\mathfrak {p}$ of $T(\mathbb {Q}_p) = \prod _{\mathfrak {p} \mid p} T_{2n}(F_\mathfrak {p})$, where

(61)\begin{equation} \begin{aligned} & \mu_\mathfrak{p}:T_{2n}(F_\mathfrak{p})\to \bar{\mathbb{Q}}_p^{\times} \text{ is given by } (\mu_{\sigma})_{\sigma\in \Sigma_\mathfrak{p}} \text{ subject to the dominance condition} \\ & \mu_{\sigma,1}\geqslant \mu_{\sigma,2}\geqslant \cdots \geqslant \mu_{\sigma,2n}, \text{ for all } \sigma\in \Sigma_\mathfrak{p}. \end{aligned} \end{equation}

Recall the maximal $(n,n)$-parabolic subgroup $Q\subseteq G$. Given a cuspidal automorphic representation $\Pi$ of $G(\mathbb {A})$ that is cohomological with respect to the weight $\mu \in X^{*}_+(T)$, we say that $\Pi _{\mathfrak {p}}$ is $Q$-ordinary (respectively, $B$-ordinary) as in [Reference HidaHid95, Reference HidaHid98].

Assume from now on that $\Pi _\mathfrak {p}$ is unramified for all $\mathfrak {p}\mid p$. As $\Pi$ is cohomological, there exists an unramified algebraic character $\lambda _{\mathfrak {p}}:T_{2n}(F_\mathfrak {p})\to \bar{\mathbb {Q}}^{\times }\subset \mathbb {C}^{\times }$ such that (see (43))

(62)\begin{equation} \Pi_\mathfrak{p}= \operatorname{Ind}_{B_{2n}(F_\mathfrak{p})}^{\operatorname{GL}_{2n}(F_\mathfrak{p})}(|\cdot|^{({2n-1})/{2}}\lambda_{\mathfrak{p}}). \end{equation}

Using $i_p: \mathbb {C} \xrightarrow {\sim } \bar{\mathbb {Q}}_p$ allows us to see the Hecke parameters $\alpha _{\mathfrak {p},i}=\lambda _{\mathfrak {p},i}(\varpi _\mathfrak {p}),\ 1\leqslant i\leqslant 2n$, as elements of $\bar{\mathbb {Q}}_p^{\times }$. Then $\Pi _\mathfrak {p}$ is $B$-ordinary relative to an ordering of its Hecke parameters $\alpha _{\mathfrak {p},i}$ if and only if

(63)\begin{equation} \big| \mu_{\mathfrak{p},i}^{\vee}(\varpi_\mathfrak{p}) \cdot q_\mathfrak{p}^{1-i} \alpha_{\mathfrak{p}, 2n+1-i} \big|_p =1, \quad \mbox{for all} \ 1\leqslant i \leqslant 2n. \end{equation}

where $|\cdot |_p$ denotes the $p$-adic norm. The $B$-dominance condition (2) then implies that

(64)\begin{equation} | \alpha_{\mathfrak{p}, 1} |_p< | \alpha_{\mathfrak{p}, 2} |_p< \cdots < | \alpha_{\mathfrak{p}, 2n}|_p, \end{equation}

hence there exists at most one ordering of the Hecke parameters for which $\Pi _\mathfrak {p}$ is $B$-ordinary. Moreover, this implies that a $B$-ordinary $\Pi _\mathfrak {p}$ is necessarily regular, that is, the $\alpha _{\mathfrak {p},i}$ are pairwise distinct.

Similarly, $\Pi _\mathfrak {p}$ is $Q$-ordinary relative to $\tau \in W_G/W_H$ if and only if

(65)\begin{equation} \prod_{i\in \tau}|\alpha_{\mathfrak{p},i}|_p = \big|q_\mathfrak{p}^{{n(n-1)}/{2}} \mu_\mathfrak{p}^{\vee}(\iota(\varpi_\mathfrak{p}^{-1}\textbf{1}_{n},\textbf{1}_{n}))\big|_p . \end{equation}

We make a key observation that $Q$-ordinarity implies $Q$-regularity (see Definition 3.5).

Lemma 4.4 Assume that the cuspidal automorphic representation $\Pi$ of $G(\mathbb {A})$ is cohomological with respect to $\mu$ and admits an $(\eta ,\psi )$-Shalika model. For $\mathfrak {p}$ dividing $p$, if $\Pi _{\mathfrak {p}}$ is spherical and $Q$-ordinary, then

\[ v_p( \alpha_{\mathfrak{p},i}) < |\Sigma_\mathfrak{p}|\frac{{{\sf w}}+2n-1}{2} < v_p( \alpha_{\mathfrak{p},i'}), \quad \text{for all } i\in \tau,\ i'\notin \tau. \]

In particular, $\Pi _{\mathfrak {p}}$ is $Q$-ordinary only relative to $\tau$. Moreover, $\tilde \Pi _{\mathfrak {p}}=(\Pi _{\mathfrak {p}},\tau )$ is $Q$-regular, that is, $q_\mathfrak {p}^{{n(1-n)}/{2}} \prod _{i\in \tau } \alpha _{\mathfrak {p},i}$ is a simple eigenvalue of $U_\mathfrak {p}$ acting on $\Pi _\mathfrak {p}^{J_\mathfrak {p}}$ and $\lambda _{\mathfrak {p}, i}\neq \lambda _{\mathfrak {p}, i'}$ for all $i\in \tau , i'\notin \tau$.

Proof. Consider the Hecke operators $U_{\mathfrak {p},n-1}=[I_{\mathfrak {p}}t_{\mathfrak {p},n-1} I_{\mathfrak {p}}]$ acting on $\Pi _{\mathfrak {p},N}^{I_\mathfrak {p}}$, where $t_{\mathfrak {p},n-1}=\operatorname {diag}(\varpi _\mathfrak {p}\textbf {1}_{n-1},\textbf {1}_{n+1})\in \operatorname {GL}_{2n}(F_\mathfrak {p})$. As $\mu _\mathfrak {p}^{\vee }(t_{\mathfrak {p},n-1})\cdot U_{\mathfrak {p},n-1}$ preserves $p$-integrality its eigenvalues on $\Pi _{\mathfrak {p},N}^{I_\mathfrak {p}}$ are $p$-integral, in particular for any $i\in \tau$ we have

(66)\begin{equation} \prod_{i\neq i' \in \tau} | \alpha_{\mathfrak{p},i'} |_p \leqslant \big|\mu_\mathfrak{p}^{\vee}(t_{\mathfrak{p},n-1}^{-1})\cdot q_\mathfrak{p}^{{(n-1)(n-2)}/{2}} \big|_p. \end{equation}

Together with (65) this implies that $|\alpha _{\mathfrak {p},i} |_p \geqslant |\mu _{\mathfrak {p},n}^{\vee }(\varpi _{\mathfrak {p}}^{-1}) q_\mathfrak {p}^{n-1}|_p= |\mu _{\mathfrak {p},n+1}(\varpi _{\mathfrak {p}}) q_\mathfrak {p}^{n-1}|_p$, that is,

(67)\begin{equation} v_p( \alpha_{\mathfrak{p},i}) \leqslant \sum_{\sigma\in \Sigma_\mathfrak{p}} (n-1+ \mu_{\sigma,n+1}). \end{equation}

The existence of $(\eta _\mathfrak {p},\psi _\mathfrak {p})$-Shalika model for $\Pi _\mathfrak {p}$ gives by [Reference Ash and GinzburgAG94, Proposition 1.3] an $i'=\rho (i)$ so that

(68)\begin{equation} v_p(\alpha_{\mathfrak{p},i})+v_p(\alpha_{\mathfrak{p},i'}) = |\Sigma_\mathfrak{p}|(2n-1+{{\sf w}}). \end{equation}

The latter equality together with (3) and (67) yields, for all $i\in \tau$,

\[ v_p( \alpha_{\mathfrak{p},i}) \leqslant \sum_{\sigma\in \Sigma_\mathfrak{p}} (n-1+ \mu_{\sigma,n+1})< |\Sigma_\mathfrak{p}|\frac{{{\sf w}}+2n-1}{2} < \sum_{\sigma\in \Sigma_\mathfrak{p}} (n+ \mu_{\sigma,n}) \leqslant v_p( \alpha_{\mathfrak{p},\rho(i)}). \]

All claims then follow easily as clearly $\rho (\tau )\cap \tau =\varnothing$ as required by Definition 3.5.

4.3 $p$-adic interpolation of critical values

We suppose in the sequel that $\Pi$ is a cuspidal automorphic representation of $G(\mathbb {A})$ that is cohomological with respect to a pure weight $\mu \in X^{*}_0(T)$ and that $\Pi$ admits an $(\eta ,\psi )$-Shalika model. Assume further that for all $\mathfrak {p}\mid p$, $\Pi _\mathfrak {p}$ is spherical and that $\tilde \Pi _\mathfrak {p}=(\Pi _\mathfrak {p}, \tau )$ is $Q$-regular for $\tau =\{n+1,\ldots , 2n\}$ in the sense of Definition 3.5.

4.3.1 Choice of local Shalika vectors

For $v\nmid p\infty$ we recall the vector $W_{\Pi _v}\in \mathcal {S}^{\eta _v}_{\psi _v}(\Pi _v)$ from Proposition 3.3.

For $\mathfrak {p} \mid p$, $\Pi _\mathfrak {p}$ is spherical and $\tilde \Pi _\mathfrak {p}=(\Pi _\mathfrak {p}, \{n+1,\ldots , 2n\})$ is $Q$-regular, in particular, $\alpha _\mathfrak {p}=\prod _{n+1\leqslant i \leqslant 2n}\alpha _{\mathfrak {p},i}$ is a simple eigenvalue for the Hecke operator $U_\mathfrak {p}$ acting on $\Pi _\mathfrak {p}^{J_\mathfrak {p}}$. By Lemma 3.6 there exists a unique $W_{\tilde \Pi _\mathfrak {p}}$ on the line $\mathcal {S}^{\eta _\mathfrak {p}}_{\psi _\mathfrak {p}}(\Pi _\mathfrak {p})^{J_\mathfrak {p}}[U_\mathfrak {p}-\alpha _\mathfrak {p}]$ normalized so that $W_{\tilde \Pi _\mathfrak {p}}(t_\mathfrak {p}^{-\delta _\mathfrak {p}})=1$. Let

(69)\begin{equation} W_{\tilde\Pi_f} = \otimes_{\mathfrak{p}\mid p}W_{\tilde\Pi_\mathfrak{p}} \bigotimes \otimes_{v\nmid p\infty}'W_{\Pi_v} \in\mathcal{S}^{\eta_f}_{\psi_f}(\Pi_f). \end{equation}

In addition to conditions (K1) and (K2) on $K$ (see § 2), we henceforth assume that:

  1. (K3) $K$ fixes $W_{\tilde \Pi _f}$ and $\eta$ is trivial on $I(\mathfrak {m})$, hence can be seen as a character of $\mathscr {C}\!\ell _F^{+}(\mathfrak {m})$.

For the local vectors at infinity, given any character $\epsilon$ of $K_{\infty }/K_\infty ^{\circ }$ we recall the basis $\Xi _\infty ^{\epsilon }$ of the line $\operatorname {H}^{t}({{\mathfrak {g}}}_\infty ,K_{\infty }^{\circ }; \mathcal {S}^{\eta _\infty }_{\psi _\infty }(\Pi _\infty )\otimes V^{\mu }_{\mathbb {C}})[\epsilon ]$ from § 4.1.3. As in [Reference Grobner and RaghuramGR14, § 4.1], we define the following.

Definition 4.5 Fix a basis $\{e_\alpha \}$ of $V^{\mu }_{\mathbb {C}}$ and a basis $\{\omega _i\}$ of $\big ({{\mathfrak {g}}}_\infty /{{\mathfrak {k}}}_\infty \big )^{\vee }$. For $\underline i= (i_1,\ldots ,i_{t}),$ with $1 \leqslant i_1 < \cdots < i_{t} \leqslant \dim \big ({{\mathfrak {g}}}_\infty /{{\mathfrak {k}}}_\infty \big )$, we let $\omega _{\underline i}= \omega _{i_1}\wedge \cdots \wedge \omega _{i_{t}}\in \bigwedge ^{t} \big ({{\mathfrak {g}}}_\infty /{{\mathfrak {k}}}_\infty \big )^{\vee }.$

Using (57), $\Xi _\infty ^{\epsilon }$ can be written as a $K_\infty ^{\circ }$-invariant element

(70)\begin{equation} \Xi_\infty^{\epsilon} = \sum_{\underline i,\alpha} \omega_{\underline i}\otimes W_{\infty,\underline i, \alpha}^{\epsilon} \otimes e_\alpha \in \wedge^{t}({{\mathfrak{g}}}_\infty/{{\mathfrak{k}}}_\infty)^{\vee} \otimes \mathcal{S}^{\eta_\infty}_{\psi_\infty}(\Pi_\infty)\otimes V^{\mu}_{\mathbb{C}}, \end{equation}

for a unique choice of $W_{\infty , \underline i, \alpha }^{\epsilon } \in \mathcal {S}^{\eta _\infty }_{\psi _\infty }(\Pi _\infty )$ called ‘cohomological vectors at infinity’.

For $\underline i$ and $\alpha$ as previously, let $\varphi _{\underline i, \alpha }^{\epsilon } \in \Pi$ be the unique vector whose image under (55) equals

\[ W^{\eta}_{\varphi_{\underline i, \alpha}^{\epsilon}}=W_{\tilde\Pi_f} \otimes W_{\infty,\underline i, \alpha}^{\epsilon} \in\mathcal{S}^{\eta}_{\psi}(\Pi). \]

For each character $\epsilon$ of $K_{\infty }/K_{\infty }^{\circ }$ the embedding $\Theta ^{\epsilon }_K$ defined in (60) yields

\[ \mathcal{S}^{\eta_f}_{\psi_f}(\Pi_f) \xrightarrow{\Theta^{\epsilon}_K} \operatorname{H}^{t}_c({S^{G}_K}, \mathcal{V}_{\mathbb{C}}^{\mu})[\epsilon] \xrightarrow{i_p^{*}} \operatorname{H}^{t}_c({S^{G}_K}, \mathcal{V}_{\bar{\mathbb{Q}}_p}^{\mu})[\epsilon] \xrightarrow{(g,v)\mapsto (g, g^{-1}\cdot v)} \operatorname{H}^{t}_c({S^{G}_K}, \mathcal{V}_{\bar{\mathbb{Q}}_p}^{\mu})[\epsilon]. \]

The image $\phi _{\tilde \Pi }^{\epsilon }$ of $W_{\tilde \Pi _f}$ under the composition of these three maps belongs to $\operatorname {H}^{t}_c({S^{G}_K}, \mathcal {V}_{E}^{\mu })[\epsilon ]$ for some finite extension $E$ of $\mathbb {Q}_p$, and after possibly rescaling the maps $\Theta ^{\epsilon }$, that is, rescaling the basis elements $\Xi _\infty ^{\epsilon }$, one can render the cohomology class $\mathcal {O}$-integral:

(71)\begin{equation} \phi_{\tilde\Pi}^{\epsilon}\in \operatorname{H}^{t}_c({S^{G}_K}, \mathcal{V}_{\mathcal{O}}^{\mu})[\epsilon]. \end{equation}

Recall that the Hecke operator $U_{p^{\beta }}^{\circ }$ defines an endomorphism of $\operatorname {H}^{t}_c({S^{G}_K}, \mathcal {V}_{\mathcal {O}}^{\mu })[\epsilon ]$. As $W_{\tilde \Pi _f}$ is an $U_{p^{\beta }}$-eigenvector with eigenvalue $\alpha _{p^{\beta }}=\prod _{\mathfrak {p}\mid p}\alpha _\mathfrak {p}^{\beta _\mathfrak {p}}$, it follows (after possibly additionally rescaling by a power of $p$ killing the torsion in $\operatorname {H}^{t}_c({S^{G}_K}, \mathcal {V}_{\mathcal {O}}^{\mu })$) that one can assume $\phi _{\tilde \Pi }^{\epsilon }$ is an $U_{p^{\beta }}^{\circ }$-eigenvector with eigenvalue $\alpha _{p^{\beta }}^{\circ }=\mu ^{\vee }(t_p^{\beta }) \alpha _{p^{\beta }}$.

4.3.2 Interpolation formula at critical points

In this section, we relate the image of $\phi _{\tilde \Pi }^{\epsilon }$ defined in (71) by the evaluation map $\mathcal {E}^{j,\eta }_{\beta ,[\delta ]}$ from (33), to the Friedberg–Jacquet integral from Proposition 4.3.

Proposition 4.6 For any character $\epsilon$ of $K_{\infty }/K_\infty ^{\circ }$ and any $[\delta ]\in \mathscr {C}\!\ell _F^{+}(p^{\beta }\mathfrak {m})\times \mathscr {C}\!\ell _F^{+}(\mathfrak {m})$ we have

\[ i_p^{-1}\big( \mu^{\vee}(t_p^{-\beta})\cdot \mathcal{E}^{j,{{\sf w}}}_{\beta,[\delta]}(\phi_{\tilde\Pi}^{\epsilon})\big)= \int_{\tilde{S}^{H}_{L_\beta}[\delta]} \varphi_{\tilde\Pi,j}^{\epsilon}(h \xi t_p^{\beta}) |\!\det(h_1^{j} h_2^{{{\sf w}}-j}) |_F \,d h, \]

where $\varphi _{\tilde \Pi ,j}^{\epsilon } = \sum _{\underline i} \sum _\alpha a_{\underline i, \alpha , j}^{\epsilon } \cdot \varphi _{\underline i, \alpha }^{\epsilon }$ for suitable $a_{\underline i, \alpha , j}^{\epsilon } \in \mathbb {C}$.

In this proposition, and henceforth, $\sum _{\underline i}$ denotes summing over all ${\underline i} = (i_1,\ldots ,i_{t})$ and $\sum _\alpha$ denotes summing over all $1 \leqslant \alpha \leqslant \dim (V^{\mu }),$ as in Definition 4.5. A more careful choice of the bases $\{e_\alpha \}$ and $\{\omega _i\}$ as in [Reference JanuszewskiJan16, § 7] yields algebraic coefficients $a_{\underline i,\alpha ,j}^{\epsilon }\in \bar {\mathbb {Q}}$.

Proof. We follow closely the proof of [Reference Barrera, Dimitrov and JorzaBDJ, Proposition 4.1]. Consider the commutative diagram

where $\tau _\beta =\mu ^{\vee }(t_p^{-\beta })\tau _\beta ^{\circ }$ is defined in (27), the horizontal maps are induced from the morphisms of local systems written above them, the map $\mathcal {T}_{\beta }$ is induced from the morphisms of local systems $(h,v)\mapsto (h\xi t_p^{\beta }, v)$, and $\operatorname {triv}'_\delta$ is induced from the morphisms of local systems:

\[ H(\mathbb{Q})\delta L_\beta H_\infty^{\circ} \times V^{(j,{{\sf w}}-j)}_{\mathbb{Q}(\tilde\Pi)} \to \mathcal{V}^{(j,{{\sf w}}-j)}_{\mathbb{Q}(\tilde\Pi)| \tilde{S}^{H}_{L_\beta}[\delta]},\quad (\gamma\delta\ell h_\infty,v)\mapsto(\gamma\delta\ell h_\infty, \gamma^{-1}\cdot v). \]

As $\mathcal {E}^{j,{{\sf w}}}_{\beta , [\delta ]}= \varepsilon (\det (\delta _{1}^{j}\delta _{2}^{{{\sf w}}-j})) \mathcal {E}^{j,{{\sf w}}}_{\beta ,\delta }$, with $\varepsilon _f = |\cdot |_{F,f}\operatorname {N}_{F_p/\mathbb {Q}_p}$, the previous diagram shows that the proposition is equivalent to

(72)\begin{equation} |\!\det(\delta_{1,f}^{j}\delta_{2,f}^{{{\sf w}}-j})|_F \big(\!\cap \theta_{[\delta]})\circ\operatorname{triv}_\delta^{*}\circ\kappa_j\circ \mathcal{T}_{\beta}\big)(\phi_{\tilde\Pi}^{\epsilon}) = \int_{\tilde{S}^{H}_{L_\beta}[\delta]} \varphi_{\tilde\Pi,j}^{\epsilon}(h\xi t_p^{\beta}) |\!\det(h_1^{j} h_2^{{{\sf w}}-j}) |_F \,d h, \end{equation}

the left-hand side being considered over $\mathbb {C}$ via $i_p^{-1}:\bar{\mathbb {Q}}_p \xrightarrow {\sim } \mathbb {C}$. By Definition 4.5

\[ \phi_{\tilde\Pi}^{\epsilon}= (\mathcal{S}^{\eta}_\psi)^{-1}( W_{\tilde\Pi_f} \otimes \Xi_\infty^{\epsilon}) = \sum_{\underline i} \sum_{\alpha} \omega_{\underline i}\otimes \varphi_{\underline i, \alpha}^{\epsilon} \otimes e_\alpha \in \big(\wedge^{t}({{\mathfrak{g}}}_\infty/{{\mathfrak{k}}}_\infty)^{\vee}\otimes \Pi \otimes V^{\mu}_{\mathbb{C}}\big)^{K_\infty^{\circ}}, \]

yielding a $V^{\mu }_{\mathbb {C}}$-valued differential $t$-form on $G_\infty ^{\circ }/K_\infty ^{\circ }$. Now, recall the basis $\kappa _j$ of the one-dimensional $\operatorname {Hom}_H(V^{\mu }, V^{(j,{{\sf w}}-j)})$ from (28) and consider the map

\[ \kappa_j\circ \iota^{*}: \operatorname{H}^{t}({{\mathfrak{g}}}_\infty,K_\infty^{\circ} ;\Pi_\infty \otimes V^{\mu}_{\mathbb{C}})\to \operatorname{H}^{t}({{\mathfrak{h}}}_\infty,L^{\circ}_\infty;\Pi_\infty \otimes V^{(j,{{\sf w}}-j)}_{\mathbb{C}}). \]

We obtain

\[ (\kappa_j\circ \mathcal{T}_{\beta})(\phi_{\tilde\Pi}^{\epsilon}) = \sum_{\underline i} \sum_\alpha \iota^{*} \omega_{\underline i} \otimes \varphi_{\underline i, \alpha}^{\epsilon}(-\cdot \xi t_p^{\beta}) \otimes \kappa_j(e_\alpha) \in \big(\wedge^{t}({{\mathfrak{h}}}_\infty/{{\mathfrak{l}}}_\infty)^{\vee}\otimes \Pi \otimes V^{(j,{{\sf w}}-j)}_{\mathbb{C}}\big)^{L_\infty^{\circ}}. \]

First, let $\kappa _j^{\circ }: V^{(j,{{\sf w}}-j)}_{\mathbb {C}}\xrightarrow {\sim } \mathbb {C}$ be the scalar extension of (40), and so $\kappa _j(e_\alpha )$ corresponds to a complex number. Next, after the discussion in the paragraph following (23), we can fix a basis for the top exterior $\wedge ^{t}({{\mathfrak {h}}}_\infty /{{\mathfrak {l}}}_\infty )^{\vee }$ corresponding to the Haar measure $dh_\infty$; hence $\iota ^{*} \omega _{\underline i}$ is a scalar multiple of $dh_\infty$. Putting both together, the restriction to $\tilde {S}^{H}_{L_\beta }[\delta ]$ of $\kappa _j( \mathcal {T}_{\beta }( \phi _{\tilde \Pi }^{\epsilon }))$ can be seen as $V^{(j,{{\sf w}}-j)}_{\mathbb {C}}$-valued top-degree differential form on $H_\infty ^{\circ }/L_\infty ^{\circ }$ given by

\[ \sum_{\underline i} \sum_\alpha a_{\underline i, \alpha, j}^{\epsilon} \cdot \varphi_{\underline i, \alpha}^{\epsilon}(\delta h_\infty \xi t_p^{\beta}) \det(h_{1,\infty}^{ j} h_{2,\infty}^{ {{\sf w}}-j}) \, d h_\infty \]

for suitable $a_{\underline i, \alpha , j}^{\epsilon }\in \mathbb {C}$. Writing $h=\gamma \delta l h'_\infty \in H(\mathbb {Q})\delta L_\beta H_\infty ^{\circ }\subset H(\mathbb {A})$, and using $\operatorname {triv}'_\delta (\gamma \delta \ell h'_\infty ,v)=(\gamma \delta \ell h'_\infty , \det (\gamma _{1,\infty }^{-j}\gamma _{2,\infty }^{j-{{\sf w}}}) v)$ one obtains (72) and the proposition from

\begin{align*} |\!\det(\delta_{1,f}^{j}\delta_{2,f}^{{{\sf w}}-j})|_F \det(\gamma_{1,\infty}^{-j}\gamma_{2,\infty}^{j-{{\sf w}}})\det(h_{1,\infty}^{ j} h_{2,\infty}^{ {{\sf w}}-j}) & = |\!\det(\delta_{1,f}^{j}\delta_{2,f}^{{{\sf w}}-j})|_F\det(h_{1,\infty}^{\prime j} h_{2,\infty}^{\prime {{\sf w}}-j})\\ & = |\!\det(h_1^{j} h_2^{{{\sf w}}-j})|_F. \end{align*}

4.3.3 $p$-adic distributions attached to $\tilde \Pi$

Recall that $\Pi$ is a cuspidal automorphic representation of $G(\mathbb {A})$ admitting a global $(\psi ,\eta )$-Shalika model, which is cohomological with respect to a pure dominant integral weight $\mu$. Recall also that $\Pi _\mathfrak {p}$ is spherical for all $\mathfrak {p}\mid p$ and that $\tilde \Pi _\mathfrak {p}=(\Pi _\mathfrak {p}, \{n+1,\ldots , 2n\})$ is $Q$-regular (see Definition 3.5), which by Lemma 4.4 is automatically fulfilled if $\Pi _\mathfrak {p}$ is $Q$-ordinary. In all cases $\Pi _\mathfrak {p}^{J_\mathfrak {p}}$ contains a unique line on which $U_\mathfrak {p}$ acts by $\alpha _{\mathfrak {p}}$. Finally recall the $U_\mathfrak {p}^{\circ }$-eigenvectors $\phi _{\tilde \Pi }^{\epsilon }$ constructed in (71). Then

(73)\begin{equation} \phi_{\tilde\Pi}=\sum_{\epsilon: F_{\infty}^{\times}/F_{\infty}^{\times\circ} \to \{\pm 1\}}\phi_{\tilde\Pi}^{\epsilon} \end{equation}

is an $U_\mathfrak {p}^{\circ }$-eigenvector with same eigenvalue. When $\tilde \Pi _p$ is $Q$-ordinary, consider the element

(74)\begin{equation} \boldsymbol{\mu}_{\tilde\Pi}^{\eta}=\boldsymbol{\mu}_{\phi_{\tilde\Pi}}^{\eta}= \varepsilon_{\operatorname{cyc}}^{-j}(\boldsymbol{\mu}^{j,\eta}_{\phi_{\tilde\Pi}})\in \mathcal{O}[[\mathscr{C}\!\ell_F^{+}(p^{\infty})]], \end{equation}

constructed in (37) and (39), which defines a measure $d\boldsymbol {\mu }_{\tilde \Pi }^{\eta }$ on $\mathscr {C}\!\ell _F^{+}(p^{\infty })$.

4.3.4 Main theorem on $p$-adic interpolation

Fix any character $\epsilon$ of $K_{\infty }/K_\infty ^{\circ }$ and any $j\in \operatorname {Crit}(\mu )$. Consider the following cohomological test vector:

(75)\begin{equation} W_{\Pi_\infty,j}^{\epsilon} = \sum_{\underline i,\alpha} a_{\underline i, \alpha, j}^{\epsilon} W_{\infty, \underline i, \alpha}^{\epsilon}. \end{equation}

A crucial result of Sun [Reference SunSun19, Theorem 5.5] asserts the following non-vanishing:

(76)\begin{equation} \zeta_\infty\big(j+\tfrac{1}{2};W_{\Pi_\infty,j}^{\epsilon}\big) \in \mathbb{C}^{\times}. \end{equation}

Note that because $\Pi _\infty \otimes {\rm sgn} = \Pi _\infty$ we have suppressed $\chi _\infty$ from the notation.

In fact, using Künneth's theorem, it is easy to see that $\zeta _\infty (j+\frac {1}{2};W_{\Pi _\infty ,j}^{\epsilon })$ is a product of similar quantities parsed over the archimedean places. As we have multiplicity one for cuspidal cohomology in top-degree (see (57)), we can only change the class $\Xi _\infty ^{\epsilon }$ by a non-zero scalar, which correspondingly scales the cohomological test vector and so also the zeta integral. The variation of the complex period $\zeta _\infty (j+\frac {1}{2};W_{\Pi _\infty ,j}^{\epsilon })$ in $j$ is studied in [Reference JanuszewskiJan16]. The reader is also referred to the discussion around [Reference Grobner and RaghuramGR14, Theorem 6.6.2].

Recall the auxiliary ideal $\mathfrak {m}$ from (L1) in § 2.1 and, for brevity, let us define

(77)\begin{equation} \gamma= \#\mathscr{C}\!\ell_F^{+}(\mathfrak{m})\cdot \# \operatorname{GL}_n(\mathcal{O}_F/\mathfrak{m})\cdot \# \operatorname{PGL}_n(\mathcal{O}_F/\mathfrak{m})\cdot \prod_{\mathfrak{p}\mid p} \big(q_\mathfrak{p}^{-n^{2}} \cdot \# \operatorname{GL}_n(\mathcal{O}_F/\mathfrak{p})\big) \in\mathbb{Q}^{\times}. \end{equation}

Theorem 4.7 Let $\Pi$ be a cuspidal automorphic representation of $\operatorname {GL}_{2n}/F$ admitting a $(\psi ,\eta )$-Shalika model and such that $\Pi _\infty$ is cohomological of weight $\mu$. Assume that for all $\mathfrak {p}\mid p$, $\Pi _\mathfrak {p}$ is spherical and admits a $Q$-regular refinement $\tilde \Pi _{\mathfrak {p}}$. Then for any $j\in \operatorname {Crit}(\mu )$ and for any finite order character $\chi$ of $\mathscr {C}\!\ell _F^{+}(p^{\infty })$ of conductor $\beta _\mathfrak {p} \geqslant 1$ at $\mathfrak {p}\mid p$:

\begin{align*} i_p^{-1}\bigg( \int_{\mathscr{C}\!\ell_F^{+}(p^{\infty})} \chi(x) \, d \boldsymbol{\mu}_{\phi_{\tilde\Pi}}^{\eta,j}(x) \bigg) &= \gamma \cdot \operatorname{N}^{jn}_{F/\mathbb{Q}}(\mathfrak{d}) \cdot \prod_{\mathfrak{p}\mid p}\big(\alpha_{\mathfrak{p}}^{-1} q_\mathfrak{p}^{n(j+1)}\big)^{\beta_\mathfrak{p}} \\ &\quad \cdot {\mathcal{G}(\chi_f)^{n} \cdot L\bigg(j+\frac{1}{2}, \Pi_f \otimes \chi_f\bigg) } \zeta_\infty\bigg(j+\frac{1}{2};W_{\Pi_\infty,j}^{(\varepsilon^{j}\chi\eta)_\infty}\bigg). \end{align*}

Proof. Using (37) and (35) we find that $\int _{\mathscr {C}\!\ell _F^{+}(p^{\infty })} \chi (x) \, d \boldsymbol {\mu }_{\phi _{\tilde \Pi }}^{\eta ,j}(x)$ equals

\[ (\alpha_{p^{\beta}}^{\circ})^{-1} \sum_{[x]\in \mathscr{C}\!\ell_F^{+}(p^{\beta}\mathfrak{m})}\chi([x])\mathcal{E}^{j,\eta}_{\beta,[x]}(\phi_{\tilde\Pi}) \nonumber = \alpha_{p^{\beta}}^{-1} \cdot \mu^{\vee}(t_p^{-\beta}) \sum_{\substack{[x]\in \mathscr{C}\!\ell_F^{+}(p^{\beta}\mathfrak{m}) \\ [y]\in \mathscr{C}\!\ell_F^{+}(\mathfrak{m})}} \chi([x]) \eta_0([y]) \mathcal{E}^{j,{{\sf w}}}_{\beta,[\delta(x,y)]}(\phi_{\tilde\Pi}). \]

As $\pi _0(\tilde {S}^{H}_{L_\beta })\simeq \mathscr {C}\!\ell _F^{+}(p^{\beta } \mathfrak {m})\times \mathscr {C}\!\ell _F^{+}(\mathfrak {m})$ by (73) and Proposition 4.6 the integral equals

\[ \alpha_{p^{\beta}}^{-1} \cdot \sum_{\epsilon: \{\pm 1\}^{\Sigma_\infty}\to \{\pm 1\}} \int_{\tilde{S}^{H}_{L_\beta}} \varphi_{\tilde\Pi,j}^{\epsilon}(h\xi t_p^{\beta}) \chi\bigg(\frac{\det(h_1)}{\det(h_2)}\bigg) \bigg| \frac{\det(h_1)}{\det(h_2)}\bigg|_F^{j} \eta^{-1}( \det(h_2)) \, d h. \]

Note that the integrand is $L_\infty ^{\circ } Z(\mathbb {A}_f)$-invariant and $L_\infty /L_\infty ^{\circ } Z_\infty$ acts on it by $\epsilon \varepsilon _\infty ^{j}\chi _\infty \eta _\infty$, hence the integral vanishes unless $\epsilon =(\varepsilon ^{j}\chi \eta )_\infty$. As $Z(\mathbb {A}_f)\cap L_\beta$ is independent of $\beta$, after some volume computation, one further finds

\[ i_p^{-1}\bigg( \int_{\mathscr{C}\!\ell_F^{+}(p^{\infty})}\varepsilon^{j}(x) \chi(x) \, d \boldsymbol{\mu}_{\tilde\Pi}^{\eta}(x)\bigg) =\gamma \cdot \Psi\bigg(j+\frac{1}{2},\varphi_{\tilde\Pi,j}^{(\varepsilon^{j}\chi\eta)_\infty}(-\cdot \xi t_p^{\beta}),\chi,\eta\bigg) \prod_{\mathfrak{p}\mid p} (\alpha_{\mathfrak{p}}^{-1} q_\mathfrak{p}^{n^{2}})^{\beta_\mathfrak{p}}. \]

By Proposition 4.3 the Friedberg–Jacquet integral has an Euler product for $\Re (s)\gg 0$:

\[ {\Psi(s,\varphi_{\tilde\Pi,j}^{\epsilon}(-\cdot \xi t_p^{\beta}),\chi,\eta)} = \prod_{v\nmid p\infty}\zeta_v(s;W_{\Pi_v},\chi_v)\cdot \prod_{\mathfrak{p}\mid p}\zeta_\mathfrak{p}(s;W_{\tilde\Pi_\mathfrak{p}}(-\cdot\xi t_\mathfrak{p}^{\beta_\mathfrak{p}}),\chi_\mathfrak{p})\cdot \zeta_\infty(s;W_{\Pi_\infty,j}^{\epsilon}, \chi_\infty). \]

As $L(s, \Pi \otimes \chi )$ has trivial Euler factors at all places $\mathfrak {p}\mid p$ (as $\Pi _\mathfrak {p}$ is spherical while $\chi _\mathfrak {p}$ is ramified), Proposition 3.3 implies that

\[ \prod_{v\nmid p\infty}\zeta_v\bigg(j+\frac{1}{2};W_{\Pi_v},\chi_v\bigg)= \operatorname{N}_{F/\mathbb{Q}}^{jn}(\mathfrak{d}^{(p)}) \chi(\mathfrak{d}^{-1})^{n} L\bigg(j+\frac{1}{2}, \Pi_f \otimes \chi_f\bigg). \]

The factor at $\mathfrak {p}\mid p$ is computed in Proposition 3.4, which together with Lemma 3.6 gives

\[ q_\mathfrak{p}^{\beta_\mathfrak{p} n^{2}} \zeta_\mathfrak{p}\big(j+\tfrac{1}{2};W_{\tilde\Pi_\mathfrak{p}},\chi_\mathfrak{p}\big) = \mathcal{G}(\chi_\mathfrak{p})^{n} \cdot q_\mathfrak{p}^{\beta_\mathfrak{p} n+ (\beta_\mathfrak{p}+\delta_\mathfrak{p})jn}W_{\tilde\Pi_\mathfrak{p}}(\textbf{1}_{2n})= \operatorname{N}_{F/\mathbb{Q}}^{jn}(\mathfrak{d}_p) \mathcal{G}(\chi_\mathfrak{p})^{n} \cdot q_\mathfrak{p}^{\beta_\mathfrak{p} n(j+1)}. \]

As $\mathcal {G}(\chi _f)=\chi (\mathfrak {d}^{-1}) \prod _{\mathfrak {p}\mid p} \mathcal {G}(\chi _\mathfrak {p})$ and $\mathfrak {d}=\mathfrak {d}_p\mathfrak {d}^{(p)}$ we obtain the desired formula.

Proof of Theorem 2 By Lemma 4.4, for each $\mathfrak {p}\mid p$, the $Q$-ordinary refinement $\tilde \Pi _\mathfrak {p}$ of $\Pi _\mathfrak {p}$ is $Q$-regular, hence Theorem 4.7 applies. The interpolation formula in Theorem B then follows immediately because by Theorem 2.3 one has

\[ \int_{\mathscr{C}\!\ell_F^{+}(p^{\infty})} \varepsilon^{j}(x) \chi(x) \, d \boldsymbol{\mu}_{\tilde\Pi}^{\eta}(x)=\int_{\mathscr{C}\!\ell_F^{+}(p^{\infty})} \chi(x) \, d \boldsymbol{\mu}_{\phi_{\tilde\Pi}}^{\eta,j}(x). \]

4.4 Non-vanishing of twists

4.4.1 The main theorem

Having established the Manin relations in our context (see Theorem 2.3), we can now prove a non-vanishing result for twisted $L$-functions using a method that goes back to Manin and Greenberg. Such a technique to prove non-vanishing of twists has also been used recently by Januszewski [Reference JanuszewskiJan18] for Rankin–Selberg $L$-functions and Eischen [Reference EischenEis] for $L$-functions of unitary groups. However, our results, Theorem 4.8 and Corollary 4.10, are not only independent of these other recent works but are also beyond the scope of results in both [Reference JanuszewskiJan18] and [Reference EischenEis] as well as previous results obtained by analytic number theoretic methods [Reference RohrlichRoh89, Reference Barthel and RamakrishnanBR94, Reference LuoLuo05, Reference Chinta, Friedberg and HoffsteinCFH05].

Theorem 4.8 Let $\mu$ be a pure dominant integral weight such that

(78)\begin{equation} \mu_{\sigma,n} > \mu_{\sigma, n+1},\quad \text{for all } \sigma\in \Sigma_\infty. \end{equation}

Let $\Pi$ be a cuspidal automorphic representation that is cohomological with respect to the weight $\mu$ and admitting an $(\eta ,\psi )$-Shalika model. Assume that for all primes $\mathfrak {p}$ above a prime number $p$, $\Pi _\mathfrak {p}$ is unramified and $Q$-ordinary. Then for all $j\in \operatorname {Crit}(\mu )$ and for all but finitely many Dirichlet characters $\chi$ of $F$ of $p$-power conductor, we have

\[ L\bigg(\frac{1}{2}+j, \Pi \otimes (\chi\circ \operatorname{N}_{F/\mathbb{Q}}) \bigg) \neq 0. \]

We begin with a few comments. As $\Pi ^{\circ } = \Pi \otimes |\cdot |^{{{\sf w}}/2}$ is a unitary cuspidal automorphic representation, we see that $({1+{{\sf w}}})/{2}$ is the center of symmetry for the $L$-function of $\Pi$:

\[ L\bigg(\frac{1+{{\sf w}}}{2}, \Pi \otimes \chi\bigg) = L\bigg(\frac{1}{2}, \Pi^{\circ}\otimes \chi\bigg). \]

By regularity one knows that $\operatorname {Crit}(\mu )$ is non-empty and condition (78) is equivalent to assuming that $\operatorname {Crit}(\mu )$ has at least two elements. If $\Pi$ is unitary, then ${{\sf w}} = 0$ and $\frac {1}{2} \in \operatorname {Crit}(\Pi \otimes \chi ) = \operatorname {Crit}(\mu )$, whence Theorem A is a particular case of Theorem 4.8.

If Leopoldt's conjecture holds for $F$ at $p$, then one readily obtains a statement for all but finitely many $p$-power conductor Hecke characters, as opposed to Dirichlet characters.

We show non-vanishing of critical values of twisted $L$-functions by showing non-vanishing statement about distributions on the cyclotomic $\mathbb {Z}_p$-extension of $F$. Recall the $p$-adic cyclotomic character

\[ \varepsilon :{\mathcal{C}\!\ell_{\mathbb{Q}}^{+}}(p^{\infty})\xrightarrow{\sim} \mathbb{Z}_p^{\times} = \mu_{2p} \times (1+2p\mathbb{Z}_p) \]

the first component of which is given by the Teichmüller character $\omega$, whereas the fixed field of the kernel of the second component $\varepsilon \omega ^{-1}$ is the cyclotomic $\mathbb {Z}_p$-extension of $\mathbb {Q}$. Then by a well-known result due to Serre there is an isomorphism $\mathcal {O}[[1+2p\mathbb {Z}_p]]\simeq \mathcal {O}[[T]]$ sending $1+2p$ to $1+T$. Composing with the norm map $\operatorname {N}_{F/\mathbb {Q}}: \mathscr {C}\!\ell _F^{+}(p^{\infty })\to {\mathcal {C}\!\ell _{\mathbb {Q}}^{+}}(p^{\infty })$ allows us to lift Dirichlet characters to Hecke characters over $F$, thus to push-forward of a measure on $\mathscr {C}\!\ell _F^{+}(p^{\infty })$, such as $\mu _{\tilde \Pi }$, to a measure on ${\mathcal {C}\!\ell _{\mathbb {Q}}^{+}}(p^{\infty })$. Further composing with $\omega ^{m}: \mu _{2p}\to \mathcal {O}^{\times }$ for $0\leqslant m \leqslant p-1$ allows us to define a measure on $1+2p\mathbb {Z}_p$, that is, an element $\omega ^{m}(\mu _{\tilde \Pi })\in \mathcal {O}[[T]]$.

Proof. We first show that $\omega ^{m}(\mu _{\tilde \Pi }) \neq 0$ for all $m\in \mathbb {Z}$. By the interpolation property in Theorem 4.7, the measure $\omega ^{m}(\mu _{\tilde \Pi })$ interpolates the algebraic parts of $L(\frac {1}{2} + j, \Pi \otimes \omega ^{m-j}\chi )$ for $j\in \operatorname {Crit}(\mu )$ and $\chi$ runs over all Dirichlet characters of (non-trivial) $p$-power order and conductor. Our hypothesis (78) implies that we find $j\in \operatorname {Crit}(\mu )$ satisfying $j> {{{\sf w}}}/{2}$, hence $\frac {1}{2} + j$ lies outside the interior of the critical strip ${w}/{2} < \Re (s) < {w}/{2}+1$ for $L(s,\Pi )$ and, thus, $L(\frac {1}{2} + j, \Pi \otimes \omega ^{m-j}\chi )\neq 0$. Therefore, $\omega ^{m}(\mu _{\tilde \Pi }) \neq 0$ as claimed.

By the Weierstrass preparation theorem, a non-zero element of $\mathcal {O}[[T]]$ admits only finitely many zeros in $\bar{\mathbb {Z}}_p$. Again by Theorem 4.7 this means that, given any $j\in \operatorname {Crit}(\mu )$ and $m$, there are at most finitely many Dirichlet characters $\chi$ of $p$-power order and conductor such that $L(\frac {1}{2} + j, \Pi \otimes \omega ^{m-j}\chi ) = 0$. As any $p$-power conductor Dirichlet character is of that form for some $0\leqslant m \leqslant p-1$, the theorem follows.

4.4.2 Variations

Corollary 4.9 Nearly ordinary case Under the hypotheses of Theorem 4.8, let $\nu$ be a finite order character of $\mathscr {C}\!\ell _F^{+}(p^{\infty })$. Then for all but finitely many Dirichlet characters $\chi$ of finite order and with $p$-power conductor, we have

\[ L\bigg(\frac{{{\sf w}}+1}{2}, \Pi\otimes\nu \chi\bigg)\neq 0. \]

Proof. Use the twisted norm map $[x]\mapsto \nu (x) [\operatorname {N}_{F/\mathbb {Q}}x]$ to push-forward $\mu _{\tilde \Pi }$ to a measure on ${\mathcal {C}\!\ell _{\mathbb {Q}}^{+}}(p^{\infty })$. Then proceed mutatis mutandis as in the proof of Theorem 4.8.

This result is slightly stronger because the representation $\Pi \otimes \nu$, even though of cohomological type and admitting a Shalika model, is no longer ordinary at $p$, nor spherical.

The following corollary of Theorem 4.8 follows from the fact that we have non-vanishing for all but finitely many Dirichlet characters $\chi$ of finite order and with $p$-power conductor.

Corollary 4.10 Simultaneous non-vanishing For $1 \leqslant k \leqslant r$ fix $n_k\in \mathbb {Z}_{>0}$ and let $\mu _k$ be a pure dominant integral weight for $\operatorname {GL}_{2n_k}$ over $F$. Suppose that each $\mu _k$ satisfies the regularity condition in (78) and that its purity weight ${{\sf w}}_k$ is even. Let $\Pi _k$ be a cuspidal automorphic representation of $\operatorname {GL}_{2n_k}(\mathbb {A}_F)$ of cohomological weight $\mu _k$ admitting a Shalika model. For a prime number $p$, suppose that each $\Pi _k$ is unramified and $Q$-ordinary at $p$. Then, for all but finitely many Dirichlet characters $\chi$ of $p$-power conductor, we have

\[ L\bigg(\frac{{{\sf w}}_{1}+1}{2}, \Pi_1\otimes \chi\bigg)L\bigg(\frac{{{\sf w}}_2+1}{2}, \Pi_2 \otimes \chi\bigg) \cdots L\bigg(\frac{{{\sf w}}_r+1}{2}, \Pi_r \otimes \chi\bigg) \neq 0. \]

Let us note that this is a simultaneous non-vanishing result at the central point. We leave it to the reader to formulate the stronger version of simultaneous non-vanishing combining Corollaries 4.9 and 4.10.

As a very concrete example illustrating an application of simultaneous non-vanishing to algebraicity results, let us consider the unitary cuspidal automorphic representation $\pi (\Delta )$ of $\operatorname {GL}_2(\mathbb {A})$ associated to the Ramanujan $\Delta$-function. A particular case of Corollary 4.10 gives infinitely many Dirichlet characters $\chi$ such that

\[ L(17, \operatorname{Sym}^{3}(\Delta)\otimes \chi) L(6, \Delta\otimes \chi) = L\big(\tfrac{1}{2}, \operatorname{Sym}^{3}(\pi(\Delta))\otimes \chi\big) L\big(\tfrac{1}{2}, \pi(\Delta)\otimes \chi\big) \neq 0. \]

For such a character we obtain from [Reference RaghuramRag10, Corollary 5.2] the following identity of $L$-values:

\[ L\big(\tfrac{1}{2}, \operatorname{Sym}^{5}(\pi(\Delta))\otimes \chi\big) = \frac{L\big(\tfrac{1}{2}, \operatorname{Sym}^{3}(\pi(\Delta)) \times \operatorname{Sym}^{2}(\pi(\Delta))\big)} {L\big(\tfrac{1}{2}, \operatorname{Sym}^{3}(\pi(\Delta))\otimes \chi\big) L\big(\tfrac{1}{2}, \pi(\Delta)\otimes \chi\big)}. \]

Using the rationality result in [Reference RaghuramRag10, Theorem 1.1] for the $L$-value in the numerator of the right-hand side, and the [Reference RaghuramRag10, Theorem 1.3] for the $L$-values in the denominator of the right-hand side, we obtain a new rationality result for

\[ L\big(\tfrac{1}{2}, \operatorname{Sym}^{5}(\pi(\Delta))\otimes \chi\big) = L\big(28, \operatorname{Sym}^{5}(\Delta)\otimes \chi\big). \]

Similarly, using the results of [Reference RaghuramRag16], and simultaneous non-vanishing for the central values of the first and third symmetric power $L$-functions of a Hilbert cusp form, one may now generalize this to get new rationality results for the symmetric fifth power $L$-functions of a Hilbert cusp form.

Acknowledgements

This project started when the three authors met at a conference in July 2014 at IISER Pune on $p$-adic aspects of modular forms. Any subset of two of the authors is grateful to the host institute or university of the third author during various stages of this work. M.D. and A.R. thank the Indo-French research agency CEFIPRA that facilitated visits by each to the workplace of the other. A.R. is grateful to the Charles Simonyi Endowment that funded his stay at the Institute for Advanced Study, Princeton.

M.D. and A.R. acknowledge support from CEFIPRA project No. 5601-1. M.D. received partial support from ANR grants CEMPI (ANR-11-LABX-0007-01) and GALF (ANR-18-CE40-0029). A.R. received partial support from MATRICS grant MTR/2018/000918, from SERB, Department of Science and Technology, Government of India.

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