$L^2$-cohomology and quasi-isometries on the ends of unbounded geometry

TL;DR

This paper investigates the invariance of minimal and maximal $L^{2}$-cohomology groups under certain quasi-isometries on unbounded ends of Riemannian manifolds, introducing new tools like a mapping cone and exploring $L^2$-signature invariance.

Contribution

It proves the invariance of $L^{2}$-cohomology groups under uniform homotopy equivalences quasi-isometric on unbounded ends, and introduces a mapping cone for $L^2$-cohomology.

Findings

$L^{2}$-cohomology groups are invariant under specified quasi-isometries.

Introduces a mapping cone construction for $L^2$-cohomology.

Shows invariance of the $L^2$-signature.

Abstract

In this paper we study the minimal and maximal $L^{2}$-cohomology of oriented, possibly not complete, Riemannian manifolds. Our focus will be on both the reduced and the unreduced $L^{2}$-cohomology groups. In particular we will prove that these groups are invariant under uniform homotopy equivalence quasi-isometric on the unbounded ends. A uniform map is a uniformly continuous map such that the diameter of the preimage of a subset is bounded in terms of the diameter of the subset itself. A map $f$ between two Riemannian manifolds $(X,g)$ and $(Y,h)$ is \textit{quasi-isometric on the unbounded ends} if $X = M \cup E_X$ where $M$ is the interior of a manifold of bounded geometry with boundary, $E_X$ is an open of $X$ and the restriction of $f$ to $E_X$ is a quasi-isometry. Finally some consequences are shown: the main ones are definition of a mapping cone for $L^2$-cohomology and the invariance of the $L^2$-signature.