## Geometry Seminar - Abstracts

### Talk

Tuesday 28 January 2020, 15:30-16:30 in HG02.802
Michael Borinsky (NIKHEF)
Renormalized topological field theory and the Euler characteristic of Out(F_n)

### Abstract

I will report on recent joint work with Karen Vogtmann on the Euler characteristic of $$\operatorname{Out}(F_n)$$ and the moduli space of graphs. A similar study has been performed in the seminal 1986 work of Harer and Zagier on the Euler characteristic of the mapping class group and the moduli space of curves. I will review a topological field theory proof, due to Kontsevich, of Harer an d Zagier's result and illustrate how an analogous 'renormalized' topological field theory argument can be applied to $$\operatorname{Out}(F_n)$$.

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