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In this article we describe the $G\times G$-equivariant $K$-ring of $X$, where $X$ is a regular compactification of a connected complex reductive algebraic group $G$. Furthermore, in the case when $G$ is a semisimple group of adjoint type,…

Algebraic Geometry · Mathematics 2007-06-12 V. Uma

In this paper we study stable finiteness of ample groupoid algebras with applications to inverse semigroup algebras and Leavitt path algebras, recovering old results and proving some new ones. In addition, we develop a theory of (faithful)…

Rings and Algebras · Mathematics 2025-10-24 Benjamin Steinberg

We present a uniqueness theorem for the reduced C*-algebra of a twist $\mathcal{E}$ over a Hausdorff \'etale groupoid $\mathcal{G}$. We show that the interior $\mathcal{I}^\mathcal{E}$ of the isotropy of $\mathcal{E}$ is a twist over the…

Operator Algebras · Mathematics 2022-06-06 Becky Armstrong

A {\it separated graph} is a pair $(E,C)$ consisting of a directed graph $E$ and a set $C=\bigsqcup_{v\in E^0}C_v$, where each $C_v$ is a partition of the set of edges whose terminal vertex is $v$. Given a separated graph $(E,C)$, such that…

Operator Algebras · Mathematics 2015-09-30 Pere Ara , Ruy Exel

We prove a finite-dimensional covariant Stinespring theorem for compact quantum groups. Let G be a compact quantum group, and let T:= Rep(G) be the rigid C*-tensor category of finite-dimensional continuous unitary representations of G. Let…

Quantum Physics · Physics 2022-09-26 Dominic Verdon

Let $G$ be a compact subgroup of $GL_n(\R)$ acting linearly on a finite dimensional vector space $E$. B. Malgrange has shown that the space $\mathcal{C}^\infty(\R^n,E)^G$ of $\mathcal{C}^\infty$ and $G$-covariant functions is a finite…

Representation Theory · Mathematics 2009-02-10 Anouar Saidi

In this work we construct a compactly generated tensor-triangulated stable category for a large class of infinite groups, including those in Kropholler's hierarchy $\mathrm{LH}\mathfrak{F}$. This can be constructed as the homotopy category…

Category Theory · Mathematics 2024-09-25 Gregory Kendall

We define equivariant semiprojectivity for C*-algebras equipped with actions of compact groups. We prove that the following examples are equivariantly semiprojective: arbitrary finite dimensional C*-algebras with arbitrary actions of…

Operator Algebras · Mathematics 2011-12-21 N. Christopher Phillips

To any dg-category $T$ (over some base ring $k$), we define a $D^{-}$-stack $\mathcal{M}_{T}$ in the sense of \cite{hagII}, classifying certain $T^{op}$-dg-modules. When $T$ is saturated, $\mathcal{M}_{T}$ classifies compact objects in the…

Algebraic Geometry · Mathematics 2007-05-23 B. Toen , M. Vaquie

Our purpose is to study in the setting of locally compact groupoids the analogues of the well-known equivalent definitions of exactness for discrete groups. Our best results are obtained for a class of \'etale groupoids that we call inner…

Operator Algebras · Mathematics 2026-03-10 Claire Anantharaman-Delaroche

If $G$ is a finite group or a torus, it is known that there is an isomorphism between the Grothendieck group of homotopy representations and that of generalized homotopy representations for $G$. We prove that there is such an isomorphism…

Algebraic Topology · Mathematics 2023-11-21 Erik Knutsen

We construct geometric models for classifying spaces of linear algebraic groups in G-equivariant motivic homotopy theory, where G is a tame group scheme. As a consequence, we show that the equivariant motivic spectrum representing the…

K-Theory and Homology · Mathematics 2020-09-16 Marc Hoyois

Quantitative algebras are algebras enriched in the category $\mathsf{Met}$ of metric spaces so that all operations are nonexpanding. Mardare, Plotkin and Panangaden introduced varieties (aka $1$-basic varieties) as classes of quantitative…

Category Theory · Mathematics 2023-01-04 Jiří Adámek , Matěj Dostál , Jiří Velebil

Given a locally coherent Grothendieck category G, we prove that the homotopy category of complexes of injective objects (also known as the coderived category of G) is compactly generated triangulated. Moreover, the full subcategory of…

Category Theory · Mathematics 2014-12-05 Jan Stovicek

We interpret certain equivariant Kasparov groups as equivariant representable K-theory groups. We compute these groups via a classifying space and as K-theory groups of suitable sigma-C*-algebras. We also relate equivariant vector bundles…

K-Theory and Homology · Mathematics 2015-10-23 Heath Emerson , Ralf Meyer

In this short note we show that the homotopy category of smooth compactifications of smooth algebraic varieties is equivalent to the homotopy category of smooth varieties over a field of characteristic zero. As an application we show that…

Algebraic Geometry · Mathematics 2013-09-03 Gereon Quick

We study the E-theory group $E_{[0,1]}(A,B)$ for a class of C*-algebras over the unit interval with finitely many singular points, called elementary $C[0,1]$-algebras. We use results on E-theory over non-Hausdorff spaces to describe…

Operator Algebras · Mathematics 2013-12-17 M. Dadarlat , P. Vaidyanathan

We study the C*-algebra crossed product $C_0(X)\rtimes G$ of a locally compact group $G$ acting properly on a locally compact Hausdorff space $X$. Under some mild extra conditions, which are automatic if $G$ is discrete or a Lie group, we…

K-Theory and Homology · Mathematics 2010-12-24 Heath Emerson , Siegfried Echterhoff

We prove that the category $\textbf{G-Cat}$ of small categories with $G$-action forms a model of unstable $G$-global homotopy theory for every discrete group $G$, generalizing Schwede's global model structure on $\textbf{Cat}$. As a…

Algebraic Topology · Mathematics 2024-10-03 Tobias Lenz

We prove that the graph C*-algebra $C^*(E)$ of a trimmable graph $E$ is $U(1)$-equivariantly isomorphic to a pullback C*-algebra of a subgraph C*-algebra $C^*(E'')$ and the C*-algebra of functions on a circle tensored with another subgraph…

K-Theory and Homology · Mathematics 2018-09-10 Francesca Arici , Francesco D'Andrea , Piotr M. Hajac , Mariusz Tobolski