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The classical Gaussian functor associates to every orthogonal representation of a locally compact group $G$ a probability measure preserving action of $G$ called a Gaussian action. In this paper, we generalize this construction by…

Dynamical Systems · Mathematics 2020-10-23 Yuki Arano , Yusuke Isono , Amine Marrakchi

In this paper we study the action of a countable group $\Gamma$ on the space of orders on the group. In particular, we are concerned with the invariant probability measures on this space, known as invariant random orders. We show that for…

Dynamical Systems · Mathematics 2022-05-20 Yair Glasner , Yuqing Frank Lin , Tom Meyerovitch

We prove that, for a free action $\alpha \colon G \curvearrowright X$ of a countably infinite discrete amenable group on a compact metric space, the small boundary property is implied by uniform property $\Gamma$ of the Cartan subalgebra…

Operator Algebras · Mathematics 2025-05-12 Grigoris Kopsacheilis , Hung-Chang Liao , Aaron Tikuisis , Andrea Vaccaro

We further develop the relationship between $\beta$-numbers and discrete curvatures to provide a new proof that under weak density assumptions, finiteness of the pointwise discrete curvature $\operatorname{curv}^{\alpha}_{\mu;2}(x,r)$ at…

Metric Geometry · Mathematics 2024-07-09 Silvia Ghinassi , Max Goering

We consider a point process sequence induced by a stationary symmetric alpha-stable (0 < alpha < 2) discrete parameter random field. It is easy to prove, following the arguments in the one-dimensional case in Resnick and Samorodnitsky…

Probability · Mathematics 2009-07-02 Parthanil Roy

We prove that for a countable discrete group $\Gamma$ containing a copy of the free group $\F_n$, for some $2\leq n\leq\infty$, as a normal subgroup, the equivalence relations of conjugacy, orbit equivalence and von Neumann equivalence of…

Dynamical Systems · Mathematics 2012-05-22 Inessa Epstein , Asger Tornquist

The extremes of a stationary time series typically occur in clusters. A primary measure for this phenomenon is the extremal index, representing the reciprocal of the expected cluster size. Both a disjoint and a sliding blocks estimator for…

Statistics Theory · Mathematics 2017-07-14 Betina Berghaus , Axel Bücher

We show that the finiteness length of an $S$-arithmetic subgroup $\Gamma$ in a noncommutative isotropic absolutely almost simple group $G$ over a global function field is one less than the sum of the local ranks of $G$ taken over the places…

Group Theory · Mathematics 2017-05-18 Kai-Uwe Bux , Ralf Köhl , Stefan Witzel

We show that in a weak globular $\omega$-category, all composition operations are equivalent and commutative for cells with sufficiently degenerate boundary, which can be considered a higher-dimensional generalisation of the Eckmann-Hilton…

Category Theory · Mathematics 2025-12-22 Thibaut Benjamin , Ioannis Markakis , Wilfred Offord , Chiara Sarti , Jamie Vicary

We survey some of the progress made recently in the classification of von Neumann algebras arising from countable groups and their measure preserving actions on probability spaces. We emphasize results which provide classes of…

Operator Algebras · Mathematics 2017-12-04 Adrian Ioana

We study the categorical-algebraic condition that internal actions are weakly representable (WRA) in the context of varieties of (non-associative) algebras over a field. Our first aim is to give a complete characterization of action…

Category Theory · Mathematics 2025-02-24 Jose Brox , Xabier García-Martínez , Manuel Mancini , Tim Van der Linden , Corentin Vienne

Suppose that G is a compact Abelian topological group, m is the Haar measure on G and f is a measurable function. Given (n_k), a strictly monotone increasing sequence of integers we consider the nonconventional ergodic/Birkhoff averages…

Dynamical Systems · Mathematics 2019-02-20 Zoltan Buczolich , Gabriella Keszthelyi

We introduce a wide class of countable groups, called properly proximal, which contains all non-amenable bi-exact groups, all non-elementary convergence groups, and all lattices in non-compact semi-simple Lie groups, but excludes all inner…

Operator Algebras · Mathematics 2018-11-15 Rémi Boutonnet , Adrian Ioana , Jesse Peterson

We develop a relative boundary theory for actions of discrete groups on compact spaces and use it to derive rigidity results for reduced crossed products. For a discrete group $\Gamma$ acting on a compact space $X$ and a subgroup $H$, we…

Operator Algebras · Mathematics 2026-01-08 Tattwamasi Amrutam , Chunlin Liu

Every absolutely summing linear operator is weakly compact. However, for strongly summing multilinear operators and polynomials - one of the most natural extensions of the linear case to the non linear framework - weak compactness does not…

Functional Analysis · Mathematics 2013-11-20 Daniel Pellegrino , Pilar Rueda , Enrique A. Sanchez-Perez

We compute the weak$^*$-dentability index of the spaces $C(K)$ where $K$ is a countable compact space. Namely ${Dz}(C([0,\omega^{\omega^\alpha}])) = \omega^{1+\alpha+1}$, whenever $0\le\alpha<\omega_1$. More generally,…

Functional Analysis · Mathematics 2009-01-10 Petr Hajek , Gilles Lancien , Antonin Prochazka

A discrete countable group \Gamma is said to be ME rigid if any discrete countable group that is measure equivalent to \Gamma is virtually isomorphic to \Gamma. In this paper, we construct ME rigid groups by amalgamating two groups…

Group Theory · Mathematics 2015-02-02 Yoshikata Kida

In this paper, we introduce topologically stable points, $\beta$-persistent points, $\beta$-persistent property, $\beta$-persistent measures and almost $\beta$-persistent measures for first countable Hausdorff group actions of compact…

Dynamical Systems · Mathematics 2021-11-23 Abdul Gaffar Khan , Tarun Das

We show that for any co-amenable compact quantum group A=C(G) there exists a unique compact Hausdorff topology on the set EA of isomorphism classes of ergodic actions of G such that the following holds: for any continuous field of ergodic…

Operator Algebras · Mathematics 2009-09-29 Hanfeng Li

We prove the uniqueness of the group measure space Cartan subalgebra in crossed products A \rtimes \Gamma covering certain cases where \Gamma is an amalgamated free product over a non-amenable subgroup. In combination with Kida's work we…

Operator Algebras · Mathematics 2013-10-01 Cyril Houdayer , Sorin Popa , Stefaan Vaes