On the unramified spectrum of spherical varieties over p-adic fields

Speaker: 

Yiannis Sakellaridis

Institution: 

Stanford University

Time: 

Thursday, October 27, 2005 - 3:00pm

Location: 

MSTB 254

Varieties with an action of a reductive group such that the Borel subgroup has an open orbit are called spherical. Spherical varieties are a unifying theme behind many analytic techniques in the theory of automorphic forms, such as the relative trace formula and integral representations of L-functions. After briefly surveying these methods - for which a general and systematic theory is missing - in order to justify this claim, I prove a general result on the representation theory of spherical varieties for split groups over p-adic fields: Irreducible quotients of the "unramified summand" of Cc&#8734(X) (where X is the spherical variety) are "roughly" parametrized by the quotient of a complex torus by a finite reflection group. This generalizes the classical parametrization of the "unramified spectrum" of G by semisimple conjugacy classes in its Langlands dual, and is compatible with recent results of D.Gaitsgory & D.Nadler which assign a "Langlands dual group" to every spherical variety. The main tool in the proof is an action, defined by F.Knop, of the Weyl group of G on the set of Borel orbits on X.

Time Reversal in a finite cavity effect of ergodicity and randomness

Speaker: 

Professor Claude Bardos

Institution: 

Paris VII & Lab of J. L. Lions

Time: 

Thursday, November 10, 2005 - 4:00pm

Location: 

MSTB 254

This talk is devoted to a mathematical analysis of the time reversal
method which was promoted by Mathias Fink, his group and others.

It involves source and transductors. The challenge is to
understand how to use as few transductors as possible.

Emphasis is put on examples of problems in a closed bounded cavity In
this situation I will describe the effect of ergodicity both when the
transductors are in the media or when they are at the boundary.

Results and methods are compared with what has already been done for
random media. Some of the proof are very similar sharper results are
obtained but only in domains with no boundary.

Classification of contractively complemented Hilbertian operator spaces.

Speaker: 

Professor Bernard Russo

Institution: 

UCI

Time: 

Tuesday, October 11, 2005 - 3:00pm

Location: 

MSTB 254

We show that every separable Hilbertian JC*-triple can be decomposed into a countable family of Hilbertian operator spaces, each of which is representable as spaces of creation or annihilation operators. This is
used to give a classification, in the category of operator spaces, of Hilbert spaces which are the range of a contractive projection on a C*-algebra.
(joint work with Matt Neal)

Right-veering diffeomorphisms of a compact surface with boundary

Speaker: 

Professor Ko Honda

Institution: 

University of Southern California

Time: 

Tuesday, October 11, 2005 - 4:00pm

Location: 

MSTB 254

We initiate the study of the monoid of right-veering diffeomorphisms on a compact oriented surface with nonempty boundary. The monoid strictly contains the monoid of products of positive Dehn twists. We explain the relationship to tight contact structures and open book decompositions. This is joint work with W. Kazez and G. Mati\'c.

Existence and regularity of stable branched minimal hypersurfaces

Speaker: 

Professor Neshan Wickramasekera

Institution: 

UCSD

Time: 

Tuesday, November 15, 2005 - 3:00pm

Location: 

MSTB 254

I will describe some recent progress on the regularity theory
for minimal hypersurfaces. Assuming stability of the hypersurfaces, the results to be presented establish a rather complete local regularity theory that is applicable near points of volume density less than 3. I will also present an existence result. The latter is joint work with
Leon Simon.

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