We prove the Novikov conjecture on oriented Cheeger spaces whose fundamental group satisfies the strong Novikov conjecture. A Cheeger space is a stratified pseudomanifold admitting, through a choice of ideal boundary conditions, an L 2 -de Rham cohomology theory satisfying Poincaré duality. We prove that this cohomology theory is invariant under stratified homotopy equivalences and that its signature is invariant under Cheeger space cobordism. Analogous results, after coupling with a Mischenko bundle associated to any Galois covering, allow us to carry out the analytic approach to the Novikov conjecture: we define higher analytic signatures of a Cheeger space and prove that they are stratified homotopy invariants whenever the assembly map is rationally injective. Finally we show that the analytic signature of a Cheeger space coincides with its topological signature as defined by Banagl.
ContentsThe authors are happy to thank Markus Banagl, Jochen Brüning, Jeff Cheeger, Greg Friedman, Michel Hilsum and Richard Melrose for many useful and interesting discussions. Thanks are also due to the referee for a careful reading of the original manuscript and for interesting remarks.
1.Smoothly stratified spaces, iie metrics, and mezzoperversities 1.1. Smoothly stratified spaces. There are many notions of stratified space [Klo09]. Most of them agree that a stratified space X is a locally compact, second countable, Hausdorff topological space endowed with a locally finite (disjoint) decompositionwhose elements, called strata, are locally closed and verify the frontier condition:The depth of a stratum Y is the largest integer k such that there is a chain of strata Y = Y k , . . . , Y 0 with Y j ⊂ Y j−1 for 1 ≤ j ≤ k. A stratum of maximal depth is always a closed manifold. The maximal depth of any stratum in X is called the depth of X as a stratified space. Thus a stratified space of depth 0 is a smooth manifold with no singularity.Where the definitions differ is on how much regularity to impose on the strata and how the strata 'fit together'. In this paper we shall mainly consider smoothly stratified pseudomanifolds with Thom-Mather control data. We proceed to recall the definition, directly taken from [BHS91] and [ALMP12].Definition 1.1. A smoothly stratified space of depth 0 is a closed manifold. Let k ∈ N, assume that the concept of smoothly stratified space of depth ≤ k has been defined. A smoothly stratified space X of depth k + 1 is a locally compact, second countable Hausdorff space which admits a locally finite decomposition into a union of locally closed strata S = {Y j }, where each Y j is a smooth (usually open) manifold, with dimension depending on the index j. We assume the following: