Continuation of last week’s talk

Speaker: Rufus Willett

Title: Positive curvature and index theory.

Abstract: Starting with two-dimensional surfaces, I’ll introduce positive (scalar) curvature. I’ll then discuss the relationship of this to index theory, a theory that counts the number of solutions to certain partial differential equations. Finally, I’ll mention the relevance of K-theory, a way of generalizing the notion of dimension of a vector space from fields to arbitrary rings.

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Title : Conformal welding homeomorphisms.

Abstract : Conformal welding is a correspondence between circle homeomorphisms and curves in the plane. It has appeared over the years to be of considerable interest in several areas of mathematics and applications, such as Teichmüller Theory, Kleinian Groups, computer vision and pattern recognition, and so forth.

The uniqueness of conformal welding has been known for a long time to be closely related to the notion of conformal removability. In fact, many papers in the literature claim, using the same argument, that uniqueness is characterized precisely by the removability of the curve. In this talk, I will show that this argument is actually incorrect, so that the problem of characterizing uniqueness of conformal welding remains open.

Title: Borel Determinacy I

Speaker: Umar Gaffar

We’re going through Ross Bryant’s presentation of Martin’s theorem (in ZFC) that Borel games are determined.

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Title: Composition semigroups on spaces of analytic functions

Abstract : A semigroup {phi_t}_{t geq 0} of analytic self-maps of the disk satisifies phi_t circ phi_s = phi_{t+s}, and induces a semigroup of composition operators. We study the maximal space of strong continuity when the composition operators act on spaces of analytic functions, particularly H^{infty}, BMOA, and the Bloch space. We show that not every composition semigroup is strongly continuous on BMOA, answering a question that had remained open in the literature since at least 1998. This is joint work with Wayne Smith and Mirjana Jovovic.