Bonn Topology Group - Abstracts

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Talk

June 16, 2026
Lennart Meier (Universiteit Utrecht): The string orientation of topological modular forms

Abstract

In the 1980s, Witten introduced the Witten genus that assigns a modular form to each closed manifold with a string structure. Ando, Hopkins and Rezk showed that this refines to an E_∞-map MString → TMF to the spectrum of topological modular forms. But their proof is very intricate. I will present a new approach to the string orientation via equivariant TMF, giving also an introduction to this theory.

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