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Bochner's theorem says that if $M$ is a compact Riemannian manifold with negative Ricci curvature, then the isometry group $\operatorname{Iso}(M)$ is finite. In this article, we show that if $(X,d,m)$ is a compact metric measure space with…

Differential Geometry · Mathematics 2020-11-12 Yifan Guo

We classify all closed, aspherical Riemannian manifolds M whose universal cover has indiscrete isometry group. One sample application is the theorem that any such M with word-hyperbolic fundamental group must be isometric to a negatively…

Differential Geometry · Mathematics 2007-05-23 Benson Farb , Shmuel Weinberger

For a space $X$ let $\mathcal{K}(X)$ be the set of compact subsets of $X$ ordered by inclusion. A map $\phi:\mathcal{K}(X) \to \mathcal{K}(Y)$ is a relative Tukey quotient if it carries compact covers to compact covers. When there is such a…

General Topology · Mathematics 2024-11-20 Ziqin Feng , Paul Gartside

We consider actions of non-compact simple Lie groups preserving an analytic rigid geometric structure of algebraic type on a compact manifold. The structure is not assumed to be unimodular, so an invariant measure may not exist. Ergodic…

Dynamical Systems · Mathematics 2009-01-06 Amos Nevo , Robert J. Zimmer

This paper is aim to extend Kenneth R. Berg's findings on the maximal entropy theorem and the ergodicity of measure convolution to the case of surjective homomorphisms. We further explores dynamical systems under surjective homomorphism in…

Dynamical Systems · Mathematics 2024-03-22 Binghui Xiao

It is well-known that a strict analogue of the Birkhoff Ergodic Theorem in infinite ergodic theory is trivial; it states that for any infinite-measure-preserving ergodic system the Birkhoff average of every integrable function is almost…

Dynamical Systems · Mathematics 2018-09-06 Marco Lenci , Sara Munday

We give necessary and sufficient conditions for joint ergodicity results of collections of sequences with respect to systems of commuting measure preserving transformations. Combining these results with a new technique that we call…

Dynamical Systems · Mathematics 2024-12-19 Nikos Frantzikinakis , Borys Kuca

We show the existence, over an arbitrary infinite ergodic $\mathbb{Z}$-dynamical system, of a generic ergodic relatively distal extension of arbitrary countable rank and arbitrary infinite compact extending groups (or more generally,…

Dynamical Systems · Mathematics 2020-09-16 Eli Glasner , Benjamin Weiss

This article is concerned with measure equivalence and uniform measure equivalence of locally compact, second countable groups. We show that two unimodular, locally compact, second countable groups are measure equivalent if and only if they…

Group Theory · Mathematics 2019-11-19 Juhani Koivisto , David Kyed , Sven Raum

For infinite products of compact spaces, Tychonoff's theorem asserts that their product is compact, in the product topology. Tychonoff's theorem is shown to be equivalent to the axiom of choice. In this paper, we show that any countable…

General Mathematics · Mathematics 2021-11-05 Garimella Sagar , Duggirala Ravi

In the framework of statistical mechanics the properties of macroscopic systems are deduced starting from the laws of their microscopic dynamics. One of the key assumptions in this procedure is the ergodic property, namely the equivalence…

Statistical Mechanics · Physics 2024-01-09 Marco Baldovin , Raffaele Marino , Angelo Vulpiani

We study the existence of uncountable first-order structures that are homogeneous with respect to their finitely generated substructures. In many classical cases this is either well-known or follows from general facts, for example, if the…

Logic · Mathematics 2025-10-21 Adam Bartoš , Wiesław Kubiś

A countable discrete group is called Choquet-Deny if for any non-degenerate probability measure on the group, the corresponding space of bounded harmonic functions is trivial. Building on the previous work of Jaworski, a complete…

Functional Analysis · Mathematics 2024-06-26 Tey Berendschot , Soham Chakraborty , Milan Donvil , Se-Jin Kim , Mario Klisse

We develop a robust structure theory for multiple ergodic averages of commuting transformations along Hardy sequences of polynomial growth. We then apply it to derive a number of novel results on joint ergodicity, recurrence and…

Dynamical Systems · Mathematics 2025-12-10 Sebastián Donoso , Andreas Koutsogiannis , Borys Kuca , Wenbo Sun , Konstantinos Tsinas

We prove a Krieger like embedding theorem for asymptotically expansive systems with the small boundary property. We show that such a system $(X; T)$ embeds in the $K$-full shift with $h_{top}(T) < \log K $ and $\sharp Per_n(X; T) \leq…

Dynamical Systems · Mathematics 2017-05-25 David Burguet

We show that under some natural ergodicity assumptions extensions given by Rokhlin cocycles lift the multiplier property if the associated locally compact group extension has only countably many L^\infty-eigenvalues. We make use of some…

Dynamical Systems · Mathematics 2009-09-23 Tim Austin , Mariusz Lemanczyk

We prove a model theorem for factor maps between ergodic, infinite measure-preserving systems.

Dynamical Systems · Mathematics 2018-03-12 Hisatoshi Yuasa

We study the properties of reflectionless measures for a Calder\'{o}n-Zygmund operator T. Roughly speaking, these are measures $\mu$ for which T(\mu) vanishes (in a weak sense) on the support of the measure. We describe the relationship…

Analysis of PDEs · Mathematics 2013-09-27 Benjamin Jaye , Fedor Nazarov

We study two properties of nonsingular and infinite measure-preserving ergodic systems: weak double ergodicity, and ergodicity with isometric coefficients. We show that there exist infinite measure-preserving transformations that are…

Dynamical Systems · Mathematics 2023-02-07 Beatrix Haddock , James Leng , Cesar E. Silva

We prove a Khintchine-type recurrence theorem for pairs of endomorphisms of a countable discrete abelian group. As a special case of the main result, if $\Gamma$ is a countable discrete abelian group, $\varphi, \psi \in End(\Gamma)$, and…

Dynamical Systems · Mathematics 2024-12-11 Ethan Ackelsberg