The mapping class group of a nonorientable surface is quasi-isometrically embedded in the mapping class group of the orientation double cover

TL;DR

This paper proves that the mapping class group of a nonorientable surface embeds quasi-isometrically into that of its orientation double cover, extending previous embedding results and utilizing the semihyperbolicity of the covering surface's mapping class group.

Contribution

It establishes the quasi-isometric embedding of the nonorientable surface's mapping class group into that of its orientation double cover, a significant extension of prior embedding results.

Findings

The embedding $ ext{Mod}(N) o ext{Mod}(S)$ is quasi-isometric.

The embedding induced by surface inclusion is quasi-isometric.

Utilizes semihyperbolicity of $ ext{Mod}(S)$ to prove results.

Abstract

Let $N$ be a connected nonorientable surface with or without boundary and punctures, and $j\colon S\rightarrow N$ be the orientation double covering. It has previously been proved that the orientation double covering $j$ induces an embedding $\iota\colon\mathrm{Mod}(N)$ $\hookrightarrow$ $\mathrm{Mod}(S)$ with one exception. In this paper, we prove that this injective homomorphism $\iota$ is a quasi-isometric embedding. The proof is based on the semihyperbolicity of $\mathrm{Mod}(S)$, which has already been established. We also prove that the embedding $\mathrm{Mod}(F') \hookrightarrow \mathrm{Mod}(F)$ induced by an inclusion of a pair of possibly nonorientable surfaces $F' \subset F$ is a quasi-isometric embedding.