Character covering number of $\mathrm{PSL}_2 (q)$

Abstract

For a group $G$ and a character $\chi$ of $G$, let $c(\chi)$ denote the set of all irreducible characters of $G$, occurring in $\chi$. We prove that whenever $q\geq 8$, all non-trivial irreducible character $\chi$ of $\mathrm{PSL}_2(q)$ satisfies $c(\chi^4)=\mathrm{Irr}\left(\mathrm{PSL}_2(q)\right)$ if $q=2^{2m+1}$ and $c(\chi^3)=\mathrm{Irr}\left(\mathrm{PSL}_2(q)\right)$ otherwise.