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THE PROBABILITY THAT $\lowercase {X}^{\lowercase {M}}$ AND $\lowercase {Y}^{\lowercase {N}}$ COMMUTE IN A COMPACT GROUP

Published online by Cambridge University Press:  02 August 2012

KARL H. HOFMANN*
Affiliation:
Fachbereich Mathematik, Technische Universität Darmstadt, Schlossgartenstr. 7, 64289 Darmstadt, Germany (email: [email protected])
FRANCESCO G. RUSSO
Affiliation:
Dieetcam, Universitá degli Studi di Palermo, Viale delle Scienze, Edificio 8, 90128, Palermo, Italy (email: [email protected])
*
For correspondence; e-mail: [email protected]
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Abstract

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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.

Type
Research Article
Copyright
Copyright © 2012 Australian Mathematical Publishing Association Inc. 

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