A stratified homotopy hypothesis

TL;DR

This paper generalizes the homotopy hypothesis to stratified spaces by embedding them into $$-categories, identifying $$-categories as striation sheaves, and constructing examples related to constructible bundles and exit-path categories.

Contribution

It provides a stratified generalization of the homotopy hypothesis, characterizes $$-categories as striation sheaves, and constructs new examples rooted in stratified geometry.

Findings

$$-categories fully faithfully embed into conically smooth stratified spaces.

Identification of $$-categories as striation sheaves with specific descent conditions.

Construction of $$-categories for constructible bundles and exit-paths.

Abstract

We show that conically smooth stratified spaces embed fully faithfully into $\infty$-categories. This articulates a stratified generalization of the homotopy hypothesis proposed by Grothendieck. As such, each $\infty$-category defines a stack on conically smooth stratified spaces, and we identify the descent conditions it satisfies. These include $\mathbb{R}^1$-invariance and descent for open covers and blow-ups, analogous to sheaves for the h-topology in $\mathbb{A}^1$-homotopy theory. In this way, we identify $\infty$-categories as striation sheaves, which are those sheaves on conically smooth stratified spaces satisfying the indicated descent. We use this identification to construct by hand two remarkable examples of $\infty$-categories: $\mathcal{B}{\sf un}$, an $\infty$-category classifying constructible bundles; and $\mathcal{E}{\sf xit}$, the absolute exit-path $\infty$-category. These constructions are deeply premised on stratified geometry, the key geometric input being a characterization of conically smooth stratified maps between cones and the existence of pullbacks for constructible bundles.