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We introduce a framework allowing for key aspects of deformation/rigidity theory to be used in the study of continuous model theory of II$_1$ factors. Using this framework, we solve several well-known open problems in the area. For example,…

Operator Algebras · Mathematics 2026-05-19 Jesse Peterson

We prove an analog of the disintegration theorem for tracial von Neumann algebras in the setting of elementary equivalence rather than isomorphism, showing that elementary equivalence of two direct integrals implies fiberwise elementary…

Operator Algebras · Mathematics 2025-07-09 David Gao , David Jekel

We call a von Neumann algebra with finite dimensional center a multifactor. We introduce an invariant of bimodules over $\rm II_1$ multifactors that we call modular distortion, and use it to formulate two classification results. We first…

Operator Algebras · Mathematics 2025-06-06 Marcel Bischoff , Ian Charlesworth , Samuel Evington , Luca Giorgetti , David Penneys

We demonstrate von Neumann algebra arising from an icc group $\Gamma$ in Chifan's, Ioana's, and Kida's class of poly-$\mathcal{C}_\text{rss} $, such as a poly-hyperbolic group with no amenable factors in its composition series, satisfies…

Operator Algebras · Mathematics 2018-02-27 Rolando de Santiago , Sujan Pant

Given a subfactor planar algebra P, Guionnet, Jones and Shlyakhtenko give a diagrammatic construction of a II_{1} subfactor whose planar algebra is P. They showed if P is finite-depth, then the factors are interpolated free group factors,…

Operator Algebras · Mathematics 2012-08-15 Michael Hartglass

We use a coarse version of the fundamental group first introduced by Barcelo, Kramer, Laubenbacher and Weaver to show that box spaces of finitely presented groups detect the normal subgroups used to construct the box space, up to…

Group Theory · Mathematics 2020-04-29 Thiebout Delabie , Ana Khukhro

Let $M$ and $N$ be smooth manifolds, with $M$ closed and connected. If the $C^r$--diffeomorphism group of $M$ is elementarily equivalent to the $C^s$--diffeomorphism group of $N$ for some $r,s\in[1,\infty)\cup\{0,\infty\}$, then $r=s$ and…

Group Theory · Mathematics 2026-01-21 Sang-hyun Kim , Thomas Koberda , J. de la Nuez González

We introduce the notion of proper proximality for finite von Neumann algebras, which naturally extends the notion of proper proximality for groups. Apart from the group von Neumann algebras of properly proximal groups, we provide a number…

Operator Algebras · Mathematics 2022-11-18 Changying Ding , Srivatsav Kunnawalkam Elayavalli , Jesse Peterson

We give a description of elementary subgroups (in the sense of first-order logic) of finitely generated virtually free groups. In particular, we recover the fact that elementary subgroups of finitely generated free groups are free factors.…

Group Theory · Mathematics 2019-12-16 Simon André

In this paper, we introduce a method computing the primitive decomposition of idempotents of any semisimple finite group algebra based on its matrix representations and Wedderburn decomposition. Particularly, we use this method to calculate…

Rings and Algebras · Mathematics 2022-06-07 Lilan Dai , Yunnan Li

Using an interplay between geometric methods in group theory and soft von Neuman algebraic techniques we prove that for any icc, acylindrically hyperbolic group $\Gamma$ its von Neumann algebra $L(\Gamma)$ satisfies the so-called ISR…

Operator Algebras · Mathematics 2023-02-17 Ionut Chifan , Sayan Das , Bin Sun

This paper addresses a conjecture of Kadison and Kastler that a von Neumann algebra M on a Hilbert space H should be unitarily equivalent to each sufficiently close von Neumann algebra N and, moreover, the implementing unitary can be chosen…

Operator Algebras · Mathematics 2013-07-30 Jan Cameron , Erik Christensen , Allan M. Sinclair , Roger R. Smith , Stuart White , Alan D. Wiggins

Using a m\'elange of techniques at the rich intersection of deformation/rigidity theory, finite index subfactor theory, and geometric group theory, we prove the existence of a continuum of property (T) factors that are pairwise non-stably…

Operator Algebras · Mathematics 2025-11-11 Ionut Chifan , Junhwi Lim

This paper shows the equivalence of the Riemann hypothesis to an sequence of elementary inequalities involving the harmonic numbers H_n, the sum of the reciprocals of the integers from 1 to n. It is a modification of a criterion due to Guy…

Number Theory · Mathematics 2007-05-23 Jeffrey C. Lagarias

We canonically associate to any planar algebra two type II_{\infty} factors M_{+} and M_{-}. The subfactors constructed previously by the authors in a previous paper are isomorphic to compressions of M_{+} and M_{-} to finite projections.…

Operator Algebras · Mathematics 2009-11-26 A. Guionnet , V. F. R. Jones , D. Shlyakhtenko

The notion of index for inclusions of von Neumann algebras goes back to a seminal work of Jones on subfactors of type ${I\!I}_1$. In the absence of a trace, one can still define the index of a conditional expectation associated to a…

Operator Algebras · Mathematics 2022-05-04 Luca Giorgetti

We provide an example of two elementarily equivalent countable ICC groups $G$ and $H$ such that $G$ is amenable and $H$ is not inner amenable. As a result, we provide the first example of elementarily equivalent groups whose group von…

Group Theory · Mathematics 2023-12-05 Isaac Goldbring

We consider, on a compact manifold, the group of diffeomorphisms that are isotopic to the identity. We show that every recurrent element is a distorsion element. This generalizes Avila's theorem on circle diffeomorphisms. The method also…

Dynamical Systems · Mathematics 2012-03-19 Emmanuel Militon

Given an isolated, quasi-homogeneous singularity $X$ we prove that there is a group isomorphism between the group of rank one reflexive sheaves on $X$ and the free abelian group generated by $\mathbb{C}^*$-divisors, modulo linear…

Algebraic Geometry · Mathematics 2023-01-13 Ananyo Dan , Agustín Romano-Velázquez

We consider the general linear group as an invariant of von Neumann factors. We prove that up to complement, a set consisting of all idempotents generating the same right ideal admits a characterisation in terms of properties of the general…

Operator Algebras · Mathematics 2017-12-29 Thierry Giordano , Adam Sierakowski
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