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Speaker:

Sebastian Hensel
Affiliation:

LMU München
Date:

Thu, 23/01/2020 - 16:30 - 17:30
Location:

MPIM Lecture Hall
Parent event:

Oberseminar Differentialgeometrie We will construct nontrivial quasimorphisms on the group of diffeomorphisms of a surface of

genus at least 2 which are isotopic to the identity. This involves considering the graph whose vertices

correspond to curves on the surface (not up to isotopy!), and transferring usual curve graph methods to

this setting. In particular, we show that it is hyperbolic, and we construct elements of Diff0(S) which act

as independent enough hyperbolic elements on it. As a consequence, we also solve a question by Burago-

Ivanov-Polterovich on the unboundedness of the fragmentation norm. This is joint work with Jonathan

Bowden and Richard Webb.

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