Chern-Weil theory for Haefliger-singular foliations

TL;DR

This paper develops a Chern-Weil theory for Haefliger-singular foliations, providing explicit characteristic forms and demonstrating their functoriality, with applications to generalizing classical invariants like the Godbillon-Vey class.

Contribution

It introduces a Chern-Weil map for singular foliations, extending characteristic class constructions to the Haefliger-singular setting with explicit forms and functorial properties.

Findings

Constructs explicit de Rham forms for characteristic classes of singular foliations.

Shows homotopy equivalence between smooth Haefliger structures and Haefliger-singular foliations.

Generalizes the Godbillon-Vey invariant to the singular setting.

Abstract

We give a Chern-Weil map for the Gel'fand-Fuks characteristic classes of Haefliger-singular foliations, those foliations defined by smooth Haefliger structures with dense regular set. Our characteristic map constructs, out of singular geometric structures adapted to singularities, explicit forms representing characteristic classes in de Rham cohomology. The forms are functorial under foliation morphisms. We prove that the theory applies, up to homotopy, to general smooth Haefliger structures: subject only to obvious necessary dimension constraints, every smooth Haefliger structure is homotopic to a Haefliger-singular foliation, and any morphism of Haefliger structures is homotopic to a morphism of Haefliger-singular foliations. As an application, we provide a generalisation to the singular setting of the classical construction of forms representing the Godbillon-Vey invariant.