On Semi-Rational Groups

TL;DR

This paper investigates the properties of semi-rational groups, providing new criteria that expand the class beyond previously known conditions, and establishes the necessity of certain conditions for simple groups, revealing new non-semi-rational groups.

Contribution

It introduces two new criteria for semi-rationality, disproves the sufficiency of Amit-Vishne condition, and constructs the first infinite family of non-semi-rational groups.

Findings

Two new criteria for semi-rationality identified.

Amit-Vishne condition is necessary for finite simple groups.

First known infinite family of non-semi-rational groups constructed.

Abstract

A finite group is called semi-rational if the distribution induced on it by any word map is a virtual character. Amit and Vishne give a sufficient condition for a group to be semi-rational, and ask whether it is also necessary. We answer this in the negative, by exhibiting two new criteria for semi-rationality, each giving rise to an infinite family of semi-rational groups which do not satisfy the Amit-Vishne condition. On the other hand, we use recent work of Lubotzky to show that for finite simple groups the Amit-Vishne condition is indeed necessary, and we use this to construct the first known example of an infinite family of non-semi-rational groups.