Blocks with the hyperfocal subgroup $Z_{2^n}\times Z_{2^n}$

Abstract

In this paper, we calculate the numbers of irreducible ordinary characters and irreducible Brauer characters in a block of a finite group $G$, whose associated fusion system over a 2-subgroup $P$ of $G$ (which is a defect group of the block) has the hyperfocal subgroup $\mathbb Z_{2^n}\times \mathbb Z_{2^n}$ for some $n\geq 2$, when the block is controlled by the normalizer $N_G(P)$ and the hyperfocal subgroup is contained in the center of $P$, or when the block is not controlled by $N_G(P)$ and the hyperfocal subgroup is contained in the center of the unique essential subgroup in the fusion system. In particular, Alperin's weight conjecture holds in the considered cases.