Higher ribbon graphs

David Nadler
University of California, Berkeley
March 12, 2018

Ribbon graphs capture the topology of open Riemann surfaces in an elementary combinatorial form. One can hope this is the first step toward a general theory for open symplectic manifolds such as Stein manifolds. We will discuss progress toward such a higher dimensional theory (joint work with Alvarez-Gavela, Eliashberg, and Starkston), and in particular, what kind of topological spaces might generalize graphs. We will also discuss applications to the calculation of symplectic invariants.

The Presend State of the Jacquet-Rallis trace formula

Pierre-Henri Chaudouard
March 9, 2018
Abstract: The Jacquet-Rallis trace formula is a powerful tool to
study periods of automorphic forms of unitary groups that show
up in Ichino-Ikeda conjecture. In this talk, I will report on the
present state of the Jacquet-Rallis trace formula. Then I will
discuss the problem of the spectral expansion. (joint work with Michal

Ax-Schanuel for Shimura Varieties

Jacob Tsimerman
University of Toronto
March 9, 2018
Abstract: (joint with N.Mok, J.Pila) Shimura varieties (S) are uniformized by symmetric spaces (H), and the uniformization map Pi:H --> S is quite transcendental. Understanding the interaction of this map with the two algebraic structures is of particular interest in arithmetic, as it is a necessary ingredient for the modern approaches to the Andre-Oort and Zilber-Pink conjectures, as well

Endoscopy and cohomology growth on unitary groups

Simon Marshall
University of Wisconsin; Member, School of Mathematics
March 9, 2018
Abstract: One of the principles of the endoscopic classification is that if an automorphic representation of a classical group is non-tempered at any place, then it should arise as a transfer from an endoscopic subgroup. One also knows that any representation of a unitary group that contributes to the cohomology of the associated symmetric space outside of middle degree must be non-tempered at infinity. By combining these two ideas, I will derive conjecturally sharp upper bounds for the growth of Betti numbers in congruence towers of complex hyperbolic manifolds.

Nodal domains for Maass forms

Peter Sarnak
Professor, School of Mathematics
March 9, 2018
Abstract: A highly excited Maass form on a hyperbolic surface
is expected to behave like a random monochromatic wave .
We will discuss this in connection with the question of the nodal
domains of such forms on arithmetic hyperbolic surfaces with a reflection symmetry .
( Joint work with A.Ghosh and A.Reznikov we will also discuss a recent result of
J.Jang and J.Jung ) .

Special cycles on simple Shimura varieties

Wei Zhang
Massachusetts Institute of Technology
March 8, 2018
Abstract: This is a work in progress inspired by the the arithmetic Gan--Gross--Prasad conjecture where one is interested in the arithmetic diagonal cycle on the product of two Shimura varieties. We study special cycles on simple Shimura varieties attached to central
simple algebras with an involution of second kind. We study some local questions arising from the relative trace formula approach.

Admissible heigh pairings of algebraic cycles

Shouwu Zhang
Princeton University
March 8, 2018
Abstract: For a smooth and projective variety X over a global field of dimension n with an adelic polarization, we propose canonical local and global height pairings for two cycles Y, Z of pure dimension p, q satisfying $p+q=n-1$. We will give some explicit arichmedean local pairings by writing down explicit formula for the diagonal green current for some Shimura varieties.