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As a generalization of the Exel-Pardo's notion of self-similar graph, we introduce self-similar group actions on ultragraphs and their $C^*$-algebras. We then approach to the $C^*$-algebras by inverse semigroup and tight groupoid models.

Operator Algebras · Mathematics 2025-05-20 Hossein Larki , Najmeh Rajabzadeh-Hasiri

We classify equivariant *-homomorphisms between C*-dynamical systems associated to actions of finite groups on C*-algebras with the Rokhlin property. In addition, the given actions are classified. An obstruction is obtained for the Cuntz…

Operator Algebras · Mathematics 2018-01-08 Eusebio Gardella , Luis Santiago

Let (g,k) be a reductive symmetric superpair of even type, i.e. so that there exists an even Cartan subspace a in p. The restriction map S(p^*)^k->S(a^*)^W where W=W(g_0:a) is the Weyl group, is injective. We determine its image explicitly.…

Representation Theory · Mathematics 2010-09-16 Alexander Alldridge , Joachim Hilgert , Martin R. Zirnbauer

Let $K$ be a normal subgroup of the finite group $H$. To a block of a $K$-interior $H$-algebra we associate a group extension, and we prove that this extension is isomorphic to an extension associated to a block given by the Brauer…

Representation Theory · Mathematics 2011-12-02 Tiberiu Coconet

This is a further investigation of our approach to group actions in homological algebra in the settings of homology of {\Gamma}-simplicial groups, particularly of {\Gamma}-equivariant homology and cohomology of {\Gamma}-groups. This…

K-Theory and Homology · Mathematics 2021-07-26 Hvedri Inassaridze

Using a new approach based on Galois theory, we study subvarieties of complex representations of reductive groups which satisfy restriction properties on their invariant rings and function fields, along the lines of the Chevalley…

Algebraic Geometry · Mathematics 2026-02-17 Bong Lian , Kamryn Spinelli

We define a Schur-Clifford subgroup of Turull's Brauer-Clifford group, similar to the Schur subgroup of the Brauer group. The Schur-Clifford subgroup contains exactly the equivalence classes coming from the intended application to Clifford…

Group Theory · Mathematics 2016-04-26 Frieder Ladisch

The study of the homology of diagram algebras has emerged as an interesting and important field. In many cases, the homology of a diagram algebra can be identified with the homology of a group. In this paper we have two main aims. Firstly,…

Algebraic Topology · Mathematics 2024-12-20 Andrew Fisher , Daniel Graves

A Hom-group G is a nonassociative version of a group where associativity, invertibility, and unitality are twisted by a map \alpha: G\longrightarrow G. Introducing the Hom-group algebra KG, we observe that Hom-groups are providing examples…

Group Theory · Mathematics 2018-03-28 Mohammad Hassanzadeh

Partial actions of groups on C*-algebras and the closely related actions and coactions of Hopf algebras received much attention over the last decades. They arise naturally as restrictions of their global counterparts to non-invariant…

Operator Algebras · Mathematics 2018-11-14 Franziska Kraken , Paula Quast , Thomas Timmermann

Let f: S'--> S be a finite and faithfully flat morphism of locally noetherian schemes of constant rank n > 1 and let G be a smooth, commutative and quasi-projective S-group scheme with connected fibers. Under certain restrictions on f and…

Number Theory · Mathematics 2019-02-13 Cristian D. Gonzalez-Aviles

The Fourier and Fourier-Stieltjes algebras over locally compact groupoids have been defined in a way that parallels their construction for groups. In this article, we extend the results on surjectivity or lack of surjectivity of the…

Functional Analysis · Mathematics 2024-11-25 Joseph DeGaetani , Mahya Ghandehari

Using equivariant obstruction theory we construct equivariant maps from certain classifying spaces to representation spheres for cyclic groups, product of elementary Abelian groups and dihedral groups. Restricting them to finite skeleta…

Algebraic Topology · Mathematics 2016-07-22 Samik Basu , Surojit Ghosh

We develop a theory of group actions and coverings on Brauer graphs that parallels the theory of group actions and coverings of algebras. In particular, we show that any Brauer graph can be covered by a tower of coverings of Brauer graphs…

Representation Theory · Mathematics 2012-12-03 Edward L Green , Sibylle Schroll , Nicole Snashall

Billey and Braden defined a geometric pattern map on flag manifolds which extends the generalized pattern map of Billey and Postnikov on Weyl groups. The interaction of this torus equivariant map with the Bruhat order and its action on line…

Algebraic Geometry · Mathematics 2016-03-15 Praise Adeyemo , Frank Sottile

We propose a new approach to study the Kronecker coefficients by using the Schur-Weyl duality between the symmetric group and the partition algebra. We explain the limiting behavior and associated bounds in the context of the partition…

Representation Theory · Mathematics 2013-02-26 Christopher Bowman , Maud De Visscher , Rosa Orellana

Let $G$ denote a reductive algebraic group over $\mathbb{C}$ and $x$ a nilpotent element of its Lie algebra $\mathfrak{g}$. The Springer variety $\mathcal{B}_x$ is the closed subvariety of the flag variety $\mathcal{B}$ of $G$…

Algebraic Geometry · Mathematics 2019-08-15 Jim Carrell , Kiumars Kaveh

We consider the action of a real reductive group G on a Kaehler manifold Z which is the restriction of a holomorphic action of the complexified group G^C. We assume that the induced action of a compatible maximal compact subgroup U of G^C…

Complex Variables · Mathematics 2007-10-08 Peter Heinzner , Patrick Schuetzdeller

We describe functorially the first Galois cohomology set $H^1({\mathbb R},G)$ of a connected reductive algebraic group $G$ over the field $\mathbb R$ of real numbers in terms of a certain action of the Weyl group on the real points of order…

Group Theory · Mathematics 2023-06-22 Mikhail Borovoi

An algebraic group is called semi-reductive if it is a semi-direct product of a reductive subgroup and the unipotent radical. Such a semi-reductive algebraic group naturally arises and also plays a key role in the study of modular…

Representation Theory · Mathematics 2021-01-19 Ke Ou , Bin Shu , Yu-Feng Yao