Published online by Cambridge University Press: 02 August 2012
In a recent article [K. H. Hofmann and F. G. Russo, ‘The probability that $x$ and
$y$ commute in a compact group’, Math. Proc. Cambridge Phil Soc., to appear] we calculated for a compact group
$G$ the probability
$d(G)$ that two randomly selected elements
$x, y\in G$ satisfy
$xy=yx$, and we discussed the remarkable consequences on the structure of
$G$ which follow from the assumption that
$d(G)$ is positive. In this note we consider two natural numbers
$m$ and
$n$ and the probability
$d_{m,n}(G)$ that for two randomly selected elements
$x, y\in G$ the relation
$x^my^n=y^nx^m$ holds. The situation is more complicated whenever
$n,m\gt 1$. If
$G$ is a compact Lie group and if its identity component
$G_0$ is abelian, then it follows readily that
$d_{m,n}(G)$ is positive. We show here that the following condition suffices for the converse to hold in an arbitrary compact group
$G$: for any nonopen closed subgroup
$H$ of
$G$, the sets
$\{g\in G: g^k\in H\}$ for both
$k=m$ and
$k=n$ have Haar measure
$0$. Indeed, we show that if a compact group
$G$ satisfies this condition and if
$d_{m,n}(G)\gt 0$, then the identity component of
$G$is abelian.