arXiv subjects

Lluis Puig

Publications and source records attributed to Lluis Puig.

18 recordsLinked to original sources

arXiv2020

The perfect F-locality from the basic F-locality over a Frobenius P-category F

Let p be a prime, P a finite p-group, F a Frobenius P-category and F^sc the full subcategory of F over the set of F-selfcentralizing subgroups of P. Recently, we have understood an easy way to obtain the perfect F^sc-locality P^sc from the basic F^sc-locality L^b: it depends on a suitable filtration of the basic F-locality L^b and on a vanishing cohomology result, given with more generality in 'Categorizations of limits of Grothendieck groups over a Frobenius P-category'.

math.GR↗

arXiv2017

A correction to the uniqueness of a partial perfect locality over a Frobenius P-category

Let $p$ be a prime, $P$ a finite p-group and $\cal F$ a Frobenius $P$-category. In "Existence, uniqueness and functoriality of the perfect locality over a Frobenius $P$-category", Algebra Colloquium, 23(2016) 541-622, we also claimed the uniqueness of the partial perfect locality $\cal L^{\frak X}$ over any up-closed set $\frak X$ of $\cal F$-selfcentralizing subgroups of $P$, but recently Bob Oliver exhibit some counter-examples, demanding some revision of our arguments. In this Note we show that, up to replacing the perfect localities by the "extendable" perfect localities over any up-closed set $\frak X$ of $\cal F$-selfcentralizing subgroups of $P$, our arguments are correct, still proving the existence and the uniqueness of the perfect $\cal F^{\rm sc}$-locality, since it is "extendable". We take advantage to simplify some of our arguments.

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arXiv2016

Note on the universality and the functoriality of the perfect F-locality

In "Frobenius Categories versus Brauer Blocks" we have proved some universality of the so-called localizing functor associated with a Frobenius $P$-category $F$, where $P$ is a finite $p$-group, with respect to the coherent $F$-localities $(\tau,L,\pi)$ such that the contravariant functor $Ker (\pi)$ maps any subgroup of $P$ to an Abelian $p$-group. The purpose of this Note is both to move from the localizing functor to the perfect locality associated with $F$ and to remove the Abelian hypothesis in the target. As a consequence, we get the functoriality for the perfect localities in the strongest form, improving the Theorem 9.15 in "Existence, uniqueness and functoriality of the perfect locality over a Frobenius $P$-category".

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arXiv2015

Categorizations of limits of Grothendieck groups over a Frobenius P-category

In "Frobenius Categories versus Brauer Blocks" and in "Ordinary Grothendieck groups of a Frobenius P-category" we consider suitable inverse limits of Grothendieck groups of categories of modules in characteristics p and zero, obtained from a so-called "folded Frobenius P-category", which covers the case of the Frobenius P-categories associated with blocks, moreover, in "Affirmative answer to a question of Linckelmann" we show that a "folded Frobenius P-category" is actually equivalent to the choice of a regular central k*-extension of the Frobenius P-category restricted to the set of F-selfcentralizing subgroups of P. Here, taking advantage of the existence of the perfect F-locality L, recently proved, we exhibit those inverse limits as the true Grothendieck groups of the categories of K*\hat G- and k*\hat G-modules for a suitable k*-group \hat G associated to the k*-category obtained from the perfect F-locality L and \hat F, both restricted to the set of F-selfcentralizing subgroups of P.

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arXiv2015

Beyond a question of Markus Linckelmann

In the 2002 Durham Symposium, Markus Linckelmann [1] conjectured the existence of a regular central k*-extension of the full subcategory over the selfcentralizing Brauer pairs of the Frobenius P-category F_{(b,G)} associated with a block b of defect group P of a finite group G, which would include, as k*-automorphism groups of the objects, the k*-groups associated with the automizers of the corresponding selfcentralizing Brauer (b,G)-pairs, introduced in [3, 6.6]; as a matter of fact, in this question the selfcentralizing Brauer pairs can be replaced by the nilcentralized Brauer pairs, still getting a positive answer. But the condition on the k*-automorphism groups of the objects is not precise enough to guarantee the uniqueness of a solution, as showed by Sejong Park in [2, Theorem 1.3]. This uniqueness depends on the folder structure [5,~Section~2] associated with F_{(b,G)} in [4,~Theorem~11.32], and here we prove the existence and the uniqueness of such a regular central k*-extension for any folded Frobenius P-category.

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arXiv2015

Existence, uniqueness and functoriality of the perfect locality over a Frobenius P-category

Let p be a prime, P a finite p-group and F a Frobenius P-category. The question on the existence of a suitable category Lsc extending the full subcategory of F over the set of F-selfcentralizing subgroups of P goes back to Dave Benson in 1994. In 2002 Carles Broto, Ran Levi and Bob Oliver formulate the existence and the uniqueness of the category Lsc in terms of the annulation of an obstruction 3-cohomology element and of the vanishing of a 2-cohomology group, and they state a sufficient condition for the vanishing of these n-cohomology groups. Recently, Amy Chermak has proved the existence and the uniqueness of Lsc via his objective partial groups, and Bob Oliver, following some of Chermak's methods, has also proved the vanishing of those n-cohomology groups for n > 1, both applying the Classification of the finite simple groups. Here we give direct proofs of the existence and the uniqueness of Lsc; moreover, in [11] we already show that Lsc can be completed in a suitable category L extending F and here we prove some functoriality of this correspondence.

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arXiv2013

A criterion on trivial homotopy

In "Homotopy decomposition of classifying spaces via elementary Abelian subgroups", Stephan Jackowski and James McClure show, for functors admitting a Mackey complement over categories holding a direct product, a general result on vanishing cohomology. We develop a framework leading to a general result on trivial homotopy which partially generalizes Jackowski and McClure's result in two different directions.

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arXiv2012

Equivariant Alperin-Robinson's Conjecture reduces to almost-simple k*-groups

In a recent paper, Gabriel Navarro and Pham Huu Tiep show that the so-called Alperin Weight Conjecture can be verified via the Classification of the Finite Simple Groups, provided any simple group fulfills a very precise list of conditions. Our purpose here is to show that the equivariant refinement of the Alperin's Conjecture for blocks formulated by Geoffrey Robinson in the eighties can be reduced to checking the same statement on any central k*-extension of any finite almost-simple group, or of any finite simple group up to verifying an "almost necessary" condition. In an Appendix we develop some old arguments that we need in the proof.

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arXiv2012

Glauberman correspondents and extensions of nilpotent block algebras

The main purpose of this paper is to prove that the extensions of a nilpotent block algebra and its Glauberman correspondent block algebra are Morita equivalent under an additional group-theoretic condition. In particular, Harris and Linckelman's theorem and Koshitani and Michler's theorem are covered. The ingredient to carry out our purpose is the two main results in Külshammer and Puig's work "Extensions of nilpotent blocks"; we actually revisited them, giving completely new proofs of both and slightly improving the second one.

math.GR↗

arXiv2011

Note on the reduction of Alperin's Conjecture

In a recent paper, Gabriel Navarro and Pham Huu Tiep show that the so-called Alperin Weight Conjecture can be verified via the Classification of the Finite Simple Groups, provided any simple group fulfills a very precise list of conditions. Our purpose here is to show to the interested reader that the results in our book "Frobenius categories versus Brauer blocks", Progress in Math. 274(2009), and the reduction arguments in "On the reduction of Alperin's Conjecture to the quasi-simple groups", J. of Algebra 328(2011), suggest a numerical statement - implying Alperin's Conjecture block by block - which can be reduced again to check that the same holds on the quasi-simple groups and, this time, this statement on the quasi-simple groups follows from the list of conditions demanded by Navarro and Tiep.

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arXiv2011

The Hecke algebra of a Frobenius P-category

We introduce a new avatar of a Frobenius P-category F in the form of a suitable sub-ring H_F of the double Burnside ring of P - called the Hecke algebra of F - where we are able to formulate the generalization to a Frobenius P-category of the Alperin Fusion Theorem, the "canonical decomposition" of the morphisms in the exterior quotient of a Frobenius P-category restricted to the selfcentralizing objects as developed in the chapter 6 of [4], the "basic P X P-sets" in the chapter 21 of [4], and the generalization by Kari Ragnarsson and Radu Stancu to the virtual P X P-sets in [6]. We also explain the relationship with the usual Hecke algebra a of finite group.

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arXiv2010

Parameterization of irreducible characters for p-solvable groups

The weights for a finite group G with respect to a prime number p where introduced by Jon Alperin, in order to formulate his celebrated conjecture. In 1992, Everett Dade formulates a refinement of Alperin's conjecture involving ordinary irreducible characters - with their defect - and, in 2000, Geoffrey Robinson proves that the new conjecture holds for p-solvable groups. But this refinement is formulated in terms of a vanishing alternating sum, without giving any possible refinement for the weights. In this note we show that, in the case of the p-solvable finite groups, the method developed in a previous paper [arXiv.org/abs/1005.3748] can be suitably refined to provide, up to the choice of a polarization, a natural bijection - namely compatible with the action of the group of outer automorphisms of G - between the sets of absolutely irreducible characters of G and of G-conjugacy classes of suitable inductive weights, preserving blocks and defects.

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arXiv2010

Weight parameterization of simple modules for p-solvable groups

The weights for a finite group G with respect to a prime number p where introduced by Jon Alperin, in order to formulate his celebrated conjecture affirming that that the number of G-conjugacy classes of weights of G coincides with the number of isomorphism classes of simple kG-modules, where k is an algebraically closed field of characteristic p. Thirty years ago, Tetsuro Okuyama already proved that in the class of p-solvable groups this conjecture holds. In this paper, for the p-solvable groups, on the one hand we exhibit a natural bijection - namely compatible with the action of the group of outer automorphisms of G - between the sets of isomorphism classes of simple G-modules M and of G-conjugacy classes of weights (R,Y), up to the choice of a polarization. On the other hand, we determine the relationship between a multiplicity module of M and Y. In an Appendix, we show that the bijection defined by Gabriel Navarro for the groups of odd order coincides with our bijection for a particular choice of the polarization.

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arXiv2010

On blocks with trivial source simple modules

Motivated by an observation in "Vertices, sources and Green correspondents of the simple modules for the large Mathieu groups", J. of Algebra 322, we determine the source algebra, and therefore all the structure, of the blocks without essential Brauer pairs where the simple modules of all the Brauer corespondents have trivial sources.

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arXiv2010

On the reduction of Alperin's Conjecture to the quasi-simple groups

We show that the refinement of Alperin's Conjecture proposed in "Frobenius Categories versus Brauer Blocks", Progress in Math. 274, can be proved by checking that this refinement holds on any central k*-extension of a finite group H containing a normal simple group S with trivial centralizer in H and p'-cyclic quotient H/S. This paper improves our result in [ibidem, Theorem 16.45] and repairs some bad arguments there.

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arXiv2010

Nilpotent extensions of blocks

There are normal sub-blocks of nilpotent blocks which are NOT nilpotent or, equivalently, nilpotent extensions of non-nilpotent blocks. In this paper we determine the source algebra structure of the non-nilpotent blocks involved in these situations. Actually, we introduce a new type of blocks - called the inertial blocks - which include the nilpotent blocks and is closed by taking normal sub-blocks.

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arXiv2010

Ordinary Grothendieck groups of a Frobenius P-category

In "Frobenius Categories versus Brauer Blocks", Progress in Math. 274, we have introduced the Frobenius categories F over a finite p-group P, and we have associated to F - suitably endowed with some central k*-extensions - a "Grothendieck group" as an inverse limit of Grothendieck groups of categories of modules in characteristic p obtained from F, determining its rank. Our purpose here is to introduce an analogous inverse limit of Grothendieck groups of categories of modules in characteristic zero obtained from F, determining its rank and proving that its extension to a field is canonically isomorphic to the direct sum of the corresponding extensions of the "Grothendieck groups" above associated with the centralizers in F of a suitable set of representatives of the F-classes of elements of P.

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arXiv2010

Frobenius P-categories via the Alperin condition

In "Frobenius Categories versus Brauer Blocks", Progress in Math. 274, we introduce the Frobenius P-categories giving two quite different definitions of them. In this paper, we exhibit a third equivalent definition based on the form of the old Alperin Fusion Theorem; this theorem can be reformulated in our abstract setting, and ultimately depends on the behavior of the so-called F-essential subgroups of P: we call "Alperin condition" a sufficient form of this behavior. Then, we prove that a divisible P-category F is a Frobenius P-category if and only if all the partial normalizers of a suitable set of representatives for the F-isomorphism classes of subgroups of P fulfill both the Sylow and the Alperin conditions.

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