Published online by Cambridge University Press: 03 April 2018
We prove that for any positive integers $k,n$ with
$n>\frac{3}{2}(k^{2}+k+2)$, prime
$p$, and integers
$c,a_{i}$, with
$p\nmid a_{i}$,
$1\leqslant i\leqslant n$, there exists a solution
$\text{}\underline{x}$ to the congruence
$$\begin{eqnarray}\mathop{\sum }_{i=1}^{n}a_{i}x_{i}^{k}\equiv c\hspace{0.6em}({\rm mod}\hspace{0.2em}p)\end{eqnarray}$$
$1\leqslant {x_{i}\ll }_{k}p^{1/k}$,
$1\leqslant i\leqslant n$. This upper bound is best possible. Refinements are given for smaller
$n$, and for variables restricted to intervals in more general position. In particular, for any
$\unicode[STIX]{x1D700}>0$ we give an explicit constant
$c_{\unicode[STIX]{x1D700}}$ such that if
$n>c_{\unicode[STIX]{x1D700}}k$, then there is a solution with
$1\leqslant {x_{i}\ll }_{\unicode[STIX]{x1D700},k}p^{1/k+\unicode[STIX]{x1D700}}$.