On groups with square-free gcd of character degree and codegree

TL;DR

This paper investigates the structure of finite groups where the greatest common divisor of each irreducible character degree and codegree is square-free, revealing that such groups are closely related to specific almost simple groups.

Contribution

It generalizes a previous result by characterizing non-solvable groups with square-free gcd of character degree and codegree, solving an open problem by Guohua Qian.

Findings

If gcd of degree and codegree is square-free for all characters, then the group modulo its solvable radical is almost simple.

The structure of these groups is limited to a specific list of almost simple groups.

The result extends understanding of the relationship between character theory and group structure.

Abstract

Let $G$ be a finite group and $\chi$ be an irreducible character of $G$. The codegree of $\chi$ is defined as $\chi^c(1) =\frac{|G: \ker\chi|}{\chi(1)}$. In a paper by Gao, Wang, and Chen, it was shown that $G$ cannot satisfy the condition that $\gcd(\chi(1),\chi^c(1))$ is prime for all $\chi\in\text{Irr}(G)^\#$. We generalize this theorem by solving one of Guohua Qian's unsolved problems on character codegrees. Qian inquires about the structure of non-solvable finite groups with square-free $\gcd$ instead. We prove that if $G$ is such that $\gcd(\chi(1),\chi^c(1))$ is square-free for every irreducible character $\chi$, then $G/\text{Sol}(G)$ is isomorphic to one among a particular list of almost simple groups.