Abstract: A quasi-morphism of a group is "a homomorphism up to a bounded error". This notion was introduced in the 80-ies in connection with bounded cohomology theory (Gromov, Brooks). It proved to be a useful tool in geometry, topology and dynamics.

In the present talk I focus on quasi-morphisms on groups of symplectic diffeomorphisms. They come from Floer theory -- the cornerstone of modern symplectic topology. I discuss a link to the theory of quasi-states - a recently emerged branch of functional analysis originated in quantum mechanics.

The talk is based on joint works math.SG/0205247, math.SG/0410338 with M.Entov and math.SG/0307011 with P.Biran and M.Entov.

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Light refreshments will be served in the faculty lounge at 3:30.

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