Matrix Discrepancy for Representations of Finite Groups

Abstract

Given a finite group $G$, we prove that there exist signs $\varepsilon\in\{\pm1\}^G$ such that $$\left\| \sum_{g\in G} \varepsilon_gρ(g) \right\|\leq C\, \sqrt{|G|},$$ where $ρ$ is the left regular representation of $G$, and $C$ is a universal constant. This special case of the Matrix Spencer conjecture was posed in [BKMZ24], where it was established for simple groups.