Browsing by Subject "Burnside ring"

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    Borel-Smith functions and the Dade group
    (Academic Press, 2007) Bouc, S.; Yalçın, E.
    We show that there is an exact sequence of biset functors over p-groups0 → Cb over(→, j) B* over(→, Ψ) DΩ → 0 where Cb is the biset functor for the group of Borel-Smith functions, B* is the dual of the Burnside ring functor, DΩ is the functor for the subgroup of the Dade group generated by relative syzygies, and the natural transformation Ψ is the transformation recently introduced by the first author in [S. Bouc, A remark on the Dade group and the Burnside group, J. Algebra 279 (2004) 180-190]. We also show that the kernel of mod 2 reduction of Ψ is naturally equivalent to the functor B× of units of the Burnside ring and obtain exact sequences involving the torsion part of DΩ, mod 2 reduction of Cb, and B×. © 2006 Elsevier Inc. All rights reserved.
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    Canonical induction, Green functors, lefschetz invariant of monomial G-posets
    (2019-06) Mutlu, Hatice
    Green functors are a kind of group functor, rather like Mackey functors, but with a further multiplicative structure. They are defined on a category whose objects are finite groups and whose morphisms are generated by maps such as induction, restriction, inflation, deflation. The aim of this thesis is general formulation for canonical induction, suitable for Green functors, optionally equipped with inflations. Let p be a prime number. In Section 3, we apply the Boltje’s theory of canonical induction [1] to p-permutation modules and give a restriction-preserving Z[1/p]- linear canonical induction formula from the inflations of projective modules. In Section 4, we give a general formulation of canonical induction theory for Green biset functors equipped with induction, restriction, inflation maps. Let G be a finite group and C be an abelian group. In Section 5, motivated in part by a search for connection with Peter Symonds’ proof [2] of the integrality of a canonical induction formula, we introduce a Lefschetz invariant for the Cmonomial Burnside ring. These invariants let us to construct generalize tensor induction functors associated to any C-monomial (G, H)-biset from the category of C-monomial G-posets to the category of C-monomial H-posets. We will show that these functors induce well-defined tensor induction maps from BC(G) to BC(H), which in turn gives a group homomorphism BC(G) × → BC(H) × between the unit groups of C-monomial Burnside rings.
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    Dade groups for finite groups and dimension functions
    (Academic Press, 2021-06-15) Gelvin, Matthew; Yalçın, Ergün
    Let G be a finite group and k an algebraically closed field of characteristic p > 0. We define the notion of a Dade kG-module as a generalization of endo-permutation modules for p-groups. We show that under a suitable equivalence relation, the set of equivalence classes of Dade kG-modules forms a group under tensor product, and the group obtained this way is isomorphic to the Dade group D(G) defined by Lassueur. We also consider the subgroup DΩ(G) of D(G) generated by relative syzygies ΩX , where X is a finite G-set. If C(G, p) denotes the group of superclass functions defined on the p-subgroups of G, there are natural generators ωX of C(G, p), and we prove the existence of a well-defined group homomorphism ΨG : C(G, p) → DΩ(G) that sends ωX to ΩX . The main theorem of the paper is the verification that the subgroup of C(G, p) consisting of the dimension functions of k-orientable real representations of G lies in the kernel of ΨG.
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    Monoid actions, their categorification and applications
    (2016-12) Erdal, Mehmet Akif
    We study actions of monoids and monoidal categories, and their relations with (co)homology theories. We start by discussing actions of monoids via bi-actions. We show that there is a well-defined functorial reverse action when a monoid action is given, which corresponds to acting by the inverses for group actions. We use this reverse actions to construct a homotopical structure on the category of monoid actions, which allow us to build the Burnside ring of a monoid. Then, we study categorifications of the previously introduced notions. In particular, we study actions of monoidal categories on categories and show that the ideas of action reversing of monoid actions extends to actions of monoidal categories. We use the reverse action for actions of monoidal categories, along with homotopy theory, to define homology, cohomology, homotopy and cohomotopy theories graded over monoidal categories. We show that most of the existing theories fits into our setting; and thus, we unify the existing definitions of these theories. Finally, we construct the spectral sequences for the theories graded over monoidal categories, which are the strongest tools for computation of cohomology and homotopy theories in existence.
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    Monomial G-posets and their Lefschetz invariants
    (Elsevier, 2019) Bouc, S.; Mutlu, Hatice
    Let G be a finite group, and C be an abelian group. We introduce the notions of C-monomial G-sets and C-monomial G-posets, and state some of their categorical properties. This gives in particular a new description of the C-monomial Burnside ring BC (G). We also introduce Lefschetz invariants of C-monomial G-posets, which are elements of BC (G). These invariants allow for a definition of a generalized tensor induction multiplicative map TU,λ : BC (G) → BC (H) associated to any C-monomial (G, H)-biset (U, λ), which in turn gives a group homomorphism BC (G)× → BC (H)× between the unit groups of C-monomial Burnside rings.
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    On the basis of the burnside ring of a fusion system
    (Elsevier, 2015) Gelvin, M.; Reeh, S.P.; Yalçın, E.
    We consider the Burnside ring A(F) of F-stable S-sets for a saturated fusion system F defined on a p-group S. It is shown by S.P. Reeh that the monoid of F-stable sets is a free commutative monoid with canonical basis {αP}. We give an explicit formula that describes αP as an S-set. In the formula we use a combinatorial concept called broken chains which we introduce to understand inverses of modified Möbius functions. © 2014 Elsevier Inc.
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    On the exponential map of the Burnside ring
    (2002) Yaman, Ayşe
    We study the exponential map of the Burnside ring. We prove the equivalence of the three different characterizations of this map and examine the surjectivity in order to describe the elements of the unit group of the Burnside ring more explicitly.
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    Rhetorical biset functors, rational p-biset functors and their semisimplicity in characteristic zero
    (Academic Press, 2008) Barker, Laurence
    Rhetorical biset functors can be defined for any family of finite groups that is closed under subquotients up to isomorphism. The rhetorical p-biset functors almost coincide with the rational p-biset functors. We show that, over a field with characteristic zero, the rhetorical biset functors are semisimple and, furthermore, they admit a character theory involving primitive characters of automorphism groups of cyclic groups.
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    Semigroup actions on sets and the burnside ring
    (Springer Science, 2018) Erdal, Mehmet Akif; Ünlü, Özgün
    In this paper we discuss some enlargements of the category of sets with semigroup actions and equivariant functions. We show that these enlarged categories possess two idempotent endofunctors. In the case of groups these enlarged categories are equivalent to the usual category of group actions and equivariant functions, and these idempotent endofunctors reverse a given action. For a general semigroup we show that these enlarged categories admit homotopical category structures defined by using these endofunctors and show that up to homotopy these categories are equivalent to the usual category of sets with semigroup actions. We finally construct the Burnside ring of a monoid by using homotopical structure of these categories, so that when the monoid is a group this definition agrees with the usual definition, and we show that when the monoid is commutative, its Burnside ring is equivalent to the Burnside ring of its Gr¨othendieck group.
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    Tornehave morphisms III: the reduced Tornehave morphism and the Burnside unit functor
    (Elsevier, 2016) Barker, L.
    We shall show that a morphism anticipated by Tornehave induces (and helps to explain) Bouc's isomorphism relating a quotient of the Burnside unit functor (measuring a difference between real and rational representations of finite 2-groups) and a quotient of the kernel of linearization (measuring a difference between rhetorical and rational 2-biset functors). © 2015 Elsevier Inc.