On the homology of big mapping class groups

Martin Palmer; Xiaolei Wu

doi:10.1112/topo.12358

Home/Archive/arXiv

arXiv · 2211.07470

On the homology of big mapping class groups

Martin Palmer·Xiaolei Wu

View original source ↗Read source document ↗Export metadata ↓

Abstract

We prove that the mapping class group of the one-holed Cantor tree surface is acyclic. This in turn determines the homology of the mapping class group of the once-punctured Cantor tree surface (i.e. the plane minus a Cantor set), in particular answering a recent question of Calegari and Chen. We in fact prove these results for a general class of infinite-type surfaces called binary tree surfaces. To prove our results we use two main ingredients: one is a modification of an argument of Mather related to the notion of dissipated groups; the other is a general homological stability result for mapping class groups of infinite-type surfaces.

Explore related subjects

math.GT math.AT math.GR

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Martin Palmer, Xiaolei Wu. 2024-09-05. On the homology of big mapping class groups. https://doi.org/10.1112/topo.12358

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

The mod 2 Seiberg-Witten invariants of spin structures and spin families

We completely determine the mod $2$ Seiberg-Witten invariants for any spin structure on any closed, oriented, smooth $4$-manifold $X$. Our computation confirms the validity of the simple type conjecture mod $2$ for spin structures. Our proof also works for families of spin $4$-manifolds and thus computes the mod $2$ Seiberg-Witten invariants for spin families. The proof of our main result uses $Pin(2)$-symmetry to define an enhancement of the mod $2$ Seiberg-Witten invariants. We prove a connected sum formula for the enhanced invariant using localisation in equivariant cohomology. Unlike the usual Seiberg-Witten invariant, the enhanced invariant does not vanish on taking connected sums and by exploiting this property, we are able to compute the enhanced invariant.

math.GT↗

arXiv2026

Schoenflies problem for area-preserving biLipschitz mappings

We prove that any biLipschitz mapping of the boundary of the unit disk onto the boundary of the domain of the same area can be extended to a biLipschitz mapping of the whole plane which preserves the area of any measurable subset.

math.GT↗

arXiv2026

Isotopy versus equivariant isotopy in dimensions three and higher

Given a finite group action on a smooth manifold, we study the following question: if two equivariant diffeomorphisms are isotopic, must they be equivariantly isotopic? Birman-Hilden and Maclachlan-Harvey proved the answer is "yes" for most surfaces. By contrast, we give a general criterion in higher dimensions under which there are many equivariant diffeomorphisms which are isotopic but not equivariantly isotopic. Examples satisfying this criterion include branched covers of split links and "stabilized" branched covers. We prove the result by constructing an invariant valued in the homology of a certain infinite cover of the manifold. We give applications to outer automorphism groups of free products and to group actions on manifolds which fiber over the circle.

math.GT↗