199 research outputs found

    Vertex and source determine the block variety of an indecomposable module

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    AbstractThe block variety VG,b(M) of a finitely generated indecomposable module M over the block algebra of a p-block b of a finite group G, introduced in (J. Algebra 215 (1999) 460), can be computed in terms of a vertex and a source of M. We use this to show that VG,b(M) is connected, and that every closed homogeneous subvariety of the affine variety VG,b defined by block cohomology H*(G,b) (cf. Algebras Rep. Theory 2 (1999) 107) is the variety of a module over the block algebra. This is analogous to the corresponding statements on Carlson's cohomology varieties in (Invent. Math. 77 (1984) 291)

    Quillen stratification for block varieties

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    AbstractThe classical results on stratifications for cohomology varieties of finite groups and their modules due to Quillen (Ann. Math. 94 (1971) 549–572; 573–602) and Avrunin–Scott (Invent. Math. 66 (1982) 277–286) carry over to the varieties associated with finitely-generated modules over p-blocks of finite groups, introduced in Linckelmann (J. Algebra 215 (1999) 460–480)

    Simple fusion systems and the Solomon 2-local groups

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    We introduce a notion of simple fusion systems which imitates the corresponding notion for finite groups and show that the fusion system on the Sylow-2-subgroup of a 7-dimensional spinor group over a field of characteristic 3 considered by Ron Solomon [18] and by Ran Levi and Bob Oliver [11] is simple in this sense

    Transfer in Hochschild Cohomology of Blocks of Finite Groups

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    Finite generation of Hochschild cohomology of Hecke algebras of finite classical type in characteristic zero

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    We show that the Hochschild cohomology HH*(ℋ) of a Hecke algebra ℋ of finite classical type over a field k of characteristic zero and a non-zero parameter q in k is finitely generated, unless possibly if q has even order in k× and ℋ is of type B or D

    On the Hilbert series of Hochschild cohomology of block algebras

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    We show that the degrees and relations of the Hochschild cohomology of a p-block algebra of a finite group over an algebraically closed field of prime characteristic p are bounded in terms of the defect groups of the block and that for a fixed defect d, there are only finitely many Hilbert series of Hochschild cohomology algebras of blocks of defect d. The main ingredients are Symondsʼ proof of Bensonʼs regularity conjecture and the fact that the Hochschild cohomology of a block is finitely generated as a module over block cohomology, which is an invariant of the fusion system of the block on a defect group
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