Localizing invariants of constructible sheaves

TL;DR

This paper introduces a novel semi-orthogonal decomposition for constructible sheaves on stratified spaces, enabling a direct sum decomposition of their localizing invariants through the exodromy equivalence.

Contribution

It constructs a new semi-orthogonal decomposition based on open-closed stratification and exodromy, revealing new adjoint functors and invariants in constructible sheaves.

Findings

New semi-orthogonal decomposition for constructible sheaves

Establishment of a direct sum decomposition of localizing invariants

Identification of strongly left adjoint functors via exodromy

Abstract

Given an open-closed decomposition of the stratifying poset, we construct a new semi-orthogonal decomposition of the $\infty$-category of constructible sheaves on a stratified space admitting an exit-path $\infty$-category. From this we obtain a direct sum decomposition of the localizing invariants of the $\infty$-category of constructible sheaves. Since the $\ast$-pullback to the open stratum in the usual (recollement) semi-orthogonal decomposition is not strongly left adjoint, this splitting does not follow from pure sheaf theory considerations. Instead, the splitting crucially relies on the exodromy equivalence: it implies that on the level of constructible sheaves, the $\ast$-pullback to a closed stratum and the $!$-pushforward from an open stratum admit left adjoints. These new functors provide an additional semi-orthogonal decomposition (with the roles of open and closed reversed) in which the relevant functors are strongly left adjoint.