Topological rigidity of the first Betti number

Abstract:

The infranil fiber bundle is a typical structure appeared in the collapsing geometry with bounded sectional curvature. In this talk, I will discuss a topological condition on the first Betti numbers that guarantees a torus fiber bundle structure (a special type of infranil fiber bundle) for collapsing manifolds with only Ricci curvature bounded below. A major technique applied here is smoothing by Ricci flows. This is a joint work with Bing Wang.