The refined transfer, bundle structures and algebraic K-theory

TL;DR

This paper develops homotopy theoretic criteria for reducing fibrations to manifold bundles, reveals new insights into homeomorphism groups, and introduces algebraic K-theory invariants to detect obstructions to smoothing fibrations.

Contribution

It introduces new criteria for fibration reduction to manifold bundles and connects algebraic K-theory invariants with smoothing obstructions, advancing the understanding of fiber bundle structures.

Findings

Homotopy theoretic criteria for fibration reduction

New results on homeomorphism groups of manifolds

Algebraic K-theory invariants detect smoothing obstructions

Abstract

We give new homotopy theoretic criteria for deciding when a fibration with homotopy finite fibers admits a reduction to a fiber bundle with compact topological manifold fibers. The criteria lead to a new and unexpected result about homeomorphism groups of manifolds. A tool used in the proof is a surjective splitting of the assembly map for Waldhausen's functor A(X). We also give concrete examples of fibrations having a reduction to a fiber bundle with compact topological manifold fibers but which fail to admit a compact fiber smoothing. The examples are detected by algebraic K-theory invariants. We consider a refinement of the Becker-Gottlieb transfer. We show that a version of the axioms described by Becker and Schultz uniquely determines the refined transfer for the class of fibrations admitting a reduction to a fiber bundle with compact topological manifold fibers. In an appendix, we sketch a theory of characteristic classes for fibrations. The classes are primary obstructions to finding a compact fiber smoothing.