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In this paper we develop a new groupoid-based structure theory for the class of regular $*$-semigroups. This class occupies something of a `sweet spot' between the important classes of inverse and regular semigroups, and contains many…

Rings and Algebras · Mathematics 2023-11-28 James East , P. A. Azeef Muhammed

In this paper we define a monoid called the equivariant Brauer semigroup for a locally compact Hausdorff groupoid E whose elements consist of Morita equivalence classes of E-dynamical systems. This construction generalizes both the…

Operator Algebras · Mathematics 2012-08-30 Jonathan Henry Brown , Geoff Goehle

The infinitesimal counterpart of a Lie groupoid is its Lie algebroid. As a vector bundle, it is given by the source vertical tangent bundle restricted to the identity bisection. Its sections can be identified with the invariant vector…

Category Theory · Mathematics 2025-11-11 Lory Aintablian , Christian Blohmann

Groupoids are the oidification of groups, and they are largely used in topology and representation theory. We consider here the category $\mathsf{Gpd}$ of all groupoids with all morphisms, and the category $\mathsf{Gpd}_\Lambda$ of…

Group Theory · Mathematics 2026-01-12 Davide Ferri

Let $(M, \varphi) = (M_1, \varphi_1) \ast (M_2, \varphi_2)$ be a free product of arbitrary von Neumann algebras endowed with faithful normal states. Assume that the centralizer $M_1^{\varphi_1}$ is diffuse. We first show that any…

Operator Algebras · Mathematics 2015-06-19 Cyril Houdayer

Computing the cohomology of the tensor product of two vector bundles is central in the study of their moduli spaces and in applications to representation theory, combinatorics and physics. These computations play a fundamental role in the…

Algebraic Geometry · Mathematics 2021-08-25 Izzet Coskun , Jack Huizenga , John Kopper

We investigate the structure of the relative bicentralizer algebra ${\rm B}(N \subset M, \varphi)$ for inclusions of von Neumann algebras with normal expectation where $N$ is a type ${\rm III_1}$ subfactor and $\varphi \in N_*$ is a…

Operator Algebras · Mathematics 2025-07-17 Hiroshi Ando , Uffe Haagerup , Cyril Houdayer , Amine Marrakchi

We relate commutative algebras in braided tensor categories to braid-reversed tensor equivalences, motivated by vertex algebra representation theory. First, for $\mathcal{C}$ a braided tensor category, we give a detailed construction of the…

Quantum Algebra · Mathematics 2022-01-14 Thomas Creutzig , Shashank Kanade , Robert McRae

Given an adaptable separated graph, we construct an associated groupoid and explore its type semigroup. Specifically, we first attach to each adaptable separated graph a corresponding semigroup, which we prove is an $E^*$-unitary inverse…

Operator Algebras · Mathematics 2020-02-03 Pere Ara , Joan Bosa , Enrique Pardo , Aidan Sims

In this work we give a generalization of matched pairs of (finite) groups to describe a general class of depth two inclusions of factor von Neumann algebras and the C*-quantum groupoids associated with, using double groupoids.

Operator Algebras · Mathematics 2007-05-23 Jean-Michel Vallin

We study graph products of groups from the viewpoint of measured group theory. We first establish a full measure equivalence classification of graph products of countably infinite groups over finite simple graphs with no transvection and no…

Group Theory · Mathematics 2024-01-10 Amandine Escalier , Camille Horbez

We introduce bounded cohomology for (pairs of) groupoids and develop homological algebra to deal with it. We generalise results of Ivanov, Frigerio and Pagliantini to this setting and show that (under topological conditions) the bounded…

Algebraic Topology · Mathematics 2018-10-16 Matthias Blank

In these notes we prove two main results: 1) It is well-known that two strongly continuous $E_0$-semigroups on $B(H)$ can be paired if and only if they have anti-isomorphic Arveson systems. For a new notion of pairing (which coincides only…

Operator Algebras · Mathematics 2025-09-05 Michael Skeide

For every partially ordered sets I, having a finite cofinal subset, and every field K we build a unital, locally matricial and hence unit-regular K-algebra B(I) such that the lattice of all its ideals is order isomorphic to the lattice of…

Rings and Algebras · Mathematics 2025-08-20 Giuseppe Baccella

In this article, we give a complete characterization of semigroup graded rings which are graded von Neumann regular. We also demonstrate our results by applying them to several classes of examples, including matrix rings and groupoid graded…

Rings and Algebras · Mathematics 2022-11-30 Daniel Lännström , Johan Öinert

A group element is called generalized torsion if a finite product of its conjugates is equal to the identity. We show that in a finitely generated abelian-by-finite group, an element is generalized torsion if and only if its image in the…

Group Theory · Mathematics 2025-12-09 Raimundo Bastos , Luis Mendonça

We generalize the notion of orbit equivalence to the non-commutative setting by introducing a new equivalence relation on groups, which we call von Neumann orbit equivalence (vNOE). We prove the stability of this equivalence relation under…

Operator Algebras · Mathematics 2026-01-14 Ishan Ishan , Aoran Wu

Let $(M, \varphi) = (M_1, \varphi_1) \ast (M_2, \varphi_2)$ be the free product of any $\sigma$-finite von Neumann algebras endowed with any faithful normal states. We show that whenever $Q \subset M$ is a von Neumann subalgebra with…

Operator Algebras · Mathematics 2016-10-05 Cyril Houdayer , Yoshimichi Ueda

A Bernstein-von Mises theorem is derived for general semiparametric functionals. The result is applied to a variety of semiparametric problems in i.i.d. and non-i.i.d. situations. In particular, new tools are developed to handle…

Statistics Theory · Mathematics 2016-08-11 Ismaël Castillo , Judith Rousseau

Let M be a von Neumann algebra of type II_1 which is also a complemented subspace of B(H). We establish an algebraic criterion, which ensures that M is an injective von Neumann algebra. As a corollary we show that if M is a complemented…

Operator Algebras · Mathematics 2014-01-13 Erik Christensen , Liguang Wang