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We present a new simple proof of the fact that certain group manifolds as well as certain homogeneous spaces G/H of dimension 4n admit a quaternionic triple of integrable complex structures that are covariantly constant with respect to the…

Mathematical Physics · Physics 2020-07-15 A. V. Smilga

We prove an explicit and sharp upper bound for the Castelnuovo-Mumford regularity of an FI-module V in terms of the degrees of its generators and relations. We use this to refine a result of Putman on the stability of homology of congruence…

Representation Theory · Mathematics 2017-06-14 Thomas Church , Jordan S. Ellenberg

We continue our study of the topology of the spaces of $m$ tuples of real polynomials with common degree $d$ and without common roots of multiplicity $n$, and in particular their stability properties with respect to $d$. In an earlier paper…

Algebraic Topology · Mathematics 2025-05-27 Andrzej Kozlowski , Kohhei Yamaguchi

We prove that for every $N\ge 3$, the group $\mathrm{Out}(F_N)$ of outer automorphisms of a free group of rank $N$ is superrigid from the point of view of measure equivalence: any countable group that is measure equivalent to…

Group Theory · Mathematics 2025-04-25 Vincent Guirardel , Camille Horbez

This paper uses the methods from arXiv:0804.1396 to give 'short' presentations for Aut$^+(F_n)$, the special automorphism group of the free group of rank $n$, and Out $^+(F_n)$ the special outer automorphism group of the free group of rank…

Group Theory · Mathematics 2021-01-12 Andrea Heald

Our goal is to find dynamic invariants that completely determine elements of the outer automorphism group $\Out(F_n)$ of the free group $F_n$ of rank $n$. To avoid finite order phenomena, we do this for {\it forward rotationless} elements.…

Group Theory · Mathematics 2009-02-16 Mark Feighn , Michael Handel

We give a criterion for separability of subgroups of certain outer automorphism groups. This answers questions of Hagen and Sisto, by strengthening and generalizing a result of theirs on mapping class groups.

Group Theory · Mathematics 2025-08-13 Francesco Fournier-Facio

Given a homeomorphism $T \colon X \to X$ of a compact metric space $X$, the stabilized automorphism group $\textrm{Aut}^{\infty}(T)$ of the system $(X,T)$ is the group of self-homeomorphisms of $X$ which commute with some power of $T$. We…

Dynamical Systems · Mathematics 2024-06-03 Jeremias Epperlein , Scott Schmieding

The observation that a graph of rank $n$ can be assembled from graphs of smaller rank $k$ with $s$ leaves by pairing the leaves together leads to a process for assembling homology classes for $Out(F_n)$ and $Aut(F_n)$ from classes for…

Algebraic Topology · Mathematics 2017-02-23 James Conant , Allen Hatcher , Martin Kassabov , Karen Vogtmann

In this paper we prove a homological stability theorem for the diffeomorphism groups of high dimensional manifolds with boundary, with respect to forming the boundary connected sum with the product $D^{p+1}\times S^{q}$ for $|q - p| <…

Algebraic Topology · Mathematics 2018-08-29 Nathan Perlmutter

We consider in parallel pointed homotopy automorphisms of iterated wedge sums of topological spaces and boundary relative homotopy automorphisms of iterated connected sums of manifolds minus a disk. Under certain conditions on the spaces…

Algebraic Topology · Mathematics 2024-08-28 Erik Lindell , Bashar Saleh

We compute the mod 2 homology of spin mapping class groups in the stable range. In earlier work we computed the stable mod p homology of the oriented mapping class group, and the methods and results here are very similar. The forgetful map…

Algebraic Topology · Mathematics 2007-05-23 Soren Galatius

We establish a homotopy-theoretic description of the homology of stable moduli spaces of $(2n+1)$-dimensional manifold triads $(N, \partial^h N, \partial^v N)$ with fixed $\partial^v N$, whenever $n \geq 3$ and $(N, \partial^h N)$ is…

Algebraic Topology · Mathematics 2025-10-22 João Lobo Fernandes

This paper, which is the second of a series of three papers, studies dynamical properties of elements of $\mathrm{Out}(F_{\tt n})$, the outer automorphism group of a nonabelian free group $F_{\tt n}$. We prove that, for every exponentially…

Group Theory · Mathematics 2022-03-09 Yassine Guerch

The ordered configuration space of $n$ open unit squares in the $w$ by $h$ rectangle exhibits homological stability in the space direction. That is, for fixed $n$ and fixed homological degree $k$, once the underlying rectangle is large…

Algebraic Topology · Mathematics 2026-02-26 Jesús González , Matthew Kahle , Nicholas Wawrykow

Trace scaling automorphisms of stable AF algebras with dimension group totally ordered are outer conjugate if the scaling factors are the same (not equal to one). This is an adaptation of a similar result for the AFD type II_infty factor by…

funct-an · Mathematics 2008-02-03 D. E. Evans , A. Kishimoto

We study holomorphic self-maps of non-ordered n-point configuration spaces C^n(X), where X is either affine or projective complex line. The complex Lie group Aut(X) acts diagonally on C^n(X). We prove that for n>4 every endomorphism F of…

Algebraic Geometry · Mathematics 2007-05-23 Vladimir Lin

We prove a homological stability theorem for moduli spaces of manifolds of dimension $2n$, for attaching handles of index at least $n$, after these manifolds have been stabilised by countably many copies of $S^n \times S^n$. Combined with…

Algebraic Topology · Mathematics 2017-02-09 Soren Galatius , Oscar Randal-Williams

We study the loxodromic elements for the action of $Out(F_n)$ on the free splitting complex of the rank $n$ free group $F_n$. We prove that each outer automorphism is either loxodromic, or has bounded orbits without any periodic point, or…

Group Theory · Mathematics 2016-06-29 Michael Handel , Lee Mosher

In this article, we show that the stabilized automorphism group of free exact odometers arising from actions of finitely generated residually finite groups coincides with the topological full group of the odometer acting on itself by right…

Group Theory · Mathematics 2026-01-13 María Isabel Cortez , Vicente Urria