Inductive Alperin bound conjecture for blocks

Let GAG\unlhd A be finite groups, let BB be a block of GG with defect group DD, and let bb be its Brauer correspondent in a subgroup MM as below. Write IBr(B)\operatorname{IBr}(B) and IBr(b)\operatorname{IBr}(b) for the sets of irreducible Brauer characters in the respective blocks. Inductive Alperin bound conjecture. There is an NA(D)\operatorname{N}_A(D)-invariant subgroup

NG(D)MG,\operatorname{N}_G(D)\leq M\leq G,

with M<GM<G whenever DD is not normal in GG, such that bb is the Brauer correspondent of BB in MM and there exists an NA(D)B\operatorname{N}_A(D)_B-invariant injection

Ω:IBr(b)IBr(B)\Omega:\operatorname{IBr}(b)\hookrightarrow\operatorname{IBr}(B)

such that

(Aχ,G,χ)b(MNA(D)ϑ,M,ϑ)(A_\chi,G,\chi)\succeq_b(M\operatorname{N}_A(D)_\vartheta,M,\vartheta)

for every ϑIBr(b)\vartheta\in\operatorname{IBr}(b) and χ=Ω(ϑ)\chi=\Omega(\vartheta). This is a blockwise refinement of Alperin's lower bound and is formulated using block isomorphisms of modular character triples. Its general validity is not established in the supplied text.

Sources & referencesView supporting material

Primary source

Zhicheng Feng, J. Miquel Martínez and Damiano Rossi, “Alperin's bound and normal Sylow subgroups”, arXiv:2502.12841 (2025).

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