Conjecture on counting unipotent irreducible Brauer characters

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Let G\mathbf{G} be a reductive algebraic group with Frobenius endomorphism FF, let G=GFG=\mathbf{G}^F, and let pp be the characteristic of the defining field. For each ℓ\ell-special unipotent element uu, let Γuℓ\Gamma_u^\ell be the ℓ\ell-special quotient defined from the projective characters of AG(u)A_{\mathbf{G}}(u). Let αℓ\alpha_\ell be the number of pairs (u,x)(u,x), where uu runs over ℓ\ell-special unipotent elements of GG up to G\mathbf{G}-conjugacy and x∈M~ℓ(Γuℓ)x\in\tilde{\mathcal{M}}_\ell(\Gamma_u^\ell).

Counting conjecture. Suppose that pp is good for G\mathbf{G}. Then αℓ\alpha_\ell is the number of unipotent irreducible Brauer characters of GG.

In characteristic zero, analogous counts use canonical quotients associated with special unipotent classes. The conjecture proposes that the ℓ\ell-special quotient gives the correct count in positive characteristic, including the modular setting relevant to bad primes.

References

Primary source

Reda Chaneb, “Basic sets for unipotent blocks of finite reductive groups in bad characteristic”, arXiv:1807.11325 (2018).

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