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To any left system of diagram categories or to any left pointed derivateur (in the sense of Grothendieck) a K-theory space is associated. This K-theory space is shown to be canonically an infinite loop space and to have a lot of common…

K-Theory and Homology · Mathematics 2007-05-23 Grigory Garkusha

The direct limit of finite-dimensional semisimple associative algebras arises as a purely algebraic counterpart to important $C^\ast$-algebras. In this paper, we classify direct limits of matrix algebras endowed with a grading by a finite…

Rings and Algebras · Mathematics 2026-01-08 Mikhail Kochetov , Felipe Yasumura

Let $\operatorname{K}_0(\operatorname{Var}_k)$ denote the Grothendieck ring of $k$-varieties over an algebraically closed field $k$. Larsen and Lunts asked if two $k$-varieties having the same class in $\operatorname{K}_0…

Algebraic Geometry · Mathematics 2019-02-20 Amit Kuber

We introduce (partially) ordered Grothendieck categories and apply results on their structure to the study of categories of representations of the Mackey Lie algebra of infinite matrices $\mathfrak{gl}^M\left(V,V_*\right)$. Here…

Representation Theory · Mathematics 2016-02-22 Alexandru Chirvasitu , Ivan Penkov

In this paper, we study $L^1$-matrix convex sets $\{K_{n}\}$ in $*$-locally convex spaces and show that every C$^*$-ordered operator space is complete isometrically, completely isomorphic to $\{A_{0}(K_{n}, M_{n}(V))\}$ for a suitable…

Operator Algebras · Mathematics 2018-02-13 Anindya Ghatak , Anil Kumar Karn

If $G$ is a finite group, the Grothendieck group ${\mathbf{K}}\_G(G)$ of the category of $G$-equivariant ${\mathbb{C}}$-vector bundles on $G$ (for the action of $G$ on itself by conjugation) is endowed with a structure of (commutative)…

Representation Theory · Mathematics 2015-09-14 Cédric Bonnafé

Using Grothendieck's "functor of points" approach to algebraic geometry, we define a new infinite-dimensional algebro-geometric flag space as a $k$-functor (for $k$ a ring) which maps a $k$-algebra $R$ to the set of certain well-ordered…

Algebraic Geometry · Mathematics 2021-12-02 Nathaniel Gallup

We prove that if two nonzero homomorphisms from the Cuntz algebra O_infinity to a purely infinite simple C*-algebra have the same class in KK-theory, and if either both are unital or both are nonunital, then they are approximately unitarily…

funct-an · Mathematics 2008-02-03 Huaxin Lin , N. Christopher Phillips

We introduce a K-theoretic invariant for actions of unitary fusion categories on unital C*-algebras. We show that for inductive limits of finite dimensional actions of fusion categories on unital AF-algebras, this is a complete invariant.…

Operator Algebras · Mathematics 2026-01-06 Quan Chen , Roberto Hernández Palomares , Corey Jones

We introduce a hierarchy for unital Kirchberg algebras with finitely generated K-groups by which the first and second homotopy groups of the automorphism groups serve as a complete invariant of classification. We also introduce an invariant…

Operator Algebras · Mathematics 2024-09-25 Kengo Matsumoto , Taro Sogabe

This paper studies a partial order on the general linear group GL(V) called the absolute order, derived from viewing GL(V) as a group generated by reflections, that is, elements whose fixed space has codimension one. The absolute order on…

Combinatorics · Mathematics 2017-10-10 Jia Huang , Joel Brewster Lewis , Victor Reiner

We investigate the relations between the Grothendieck group of coherent modules of an algebraic variety and its Chow group of algebraic cycles modulo rational equivalence. Those are in essence torsion phenomena, which we attempt to control…

Algebraic Geometry · Mathematics 2023-08-29 Olivier Haution , Alexander S. Merkurjev

We associate to each unital $C^*$-algebra $A$ a geometric object---a diagram of topological spaces representing quotient spaces of the noncommutative space underlying $A$---meant to serve the role of a generalized Gel'fand spectrum. After…

Operator Algebras · Mathematics 2014-08-07 Nadish de Silva

For every natural number k we introduce the notion of k-th order convolution of functions on abelian groups. We study the group of convolution preserving automorphisms of function algebras in the limit. It turns out that such groups have…

Combinatorics · Mathematics 2010-01-26 Balazs Szegedy

Let $k$ be an algebraically closed field of positive characteristic $p$ and let $\mathbb{G}_a$ denote the additive group of $k$. Let $n \geq 1$ and let ${\rm Mat}(n, k[T])^E$ denote the set of all exponential matrices of ${\rm Mat}(n,…

Representation Theory · Mathematics 2025-11-24 Ryuji Tanimoto

We continue the study of the effective content of $K$-theory for C*-algebras, with a focus on AF algebras. We show that from a c.e. presentation of an AF algebra it is possible to compute a representation of the algebra as an inductive…

Operator Algebras · Mathematics 2026-02-09 Christopher J. Eagle , Isaac Goldbring , Timothy H. McNicholl

For an algebraically closed field K, let G be a finite abelian group of K-linear automorphisms of a finite-dimensional path algebra KQ of a quiver Q. Under certain assumptions on the action of G, we show the existence of a certain kind of…

Representation Theory · Mathematics 2025-07-29 Shantanu Sardar , Alfredo Gonzalez Chaio , Sonia Trepode

We study the operational bivariant theory associated to the covariant theory of Grothendieck groups of coherent sheaves, and prove that it has many geometric properties analogous to those of operational Chow theory. This operational…

Algebraic Geometry · Mathematics 2015-06-10 Dave Anderson , Sam Payne

Let $O$ be the ring of power series in one variable over a finite field, with $K$ its fraction field. We introduce the notion of a "formal $K$-vector space"; this is a certain kind of $K$-vector space object in the category of formal…

Number Theory · Mathematics 2013-04-04 Jared Weinstein

Let $X$ be a smooth scheme with an action of a reductive algebraic group $G$ over an algebraically closed field $k$ of characteristic zero. We construct an action of the extended affine Braid group on the $G$-equivariant absolute derived…

Representation Theory · Mathematics 2015-10-27 Sergey Arkhipov , Tina Kanstrup