# Events for February 22, 2017 from General and Seminar calendars

## Number Theory Seminar

**Time:** 1:45PM - 2:45PM

**Location:** BLOC 220

**Speaker:** Adrian Barquero-Sanchez, Universidad de Costa Rica

**Title:** *The Chowla-Selberg formula for CM abelian surfaces*

**Abstract:**In the 80's Deligne gave a geometric reformulation of the classical Chowla-Selberg formula as an identity expressing the Faltings height of a CM elliptic curve in terms of values of Euler's Gamma function at rational arguments. In this talk I will sketch a proof of a higher dimensional analogue of Deligne's formula, expressing the Faltings height of a CM abelian surface in terms of the Barnes double Gamma function at certain algebraic numbers. This is joint work with Riad Masri.

**URL:** *Link*

## Noncommutative Geometry Seminar

**Time:** 2:00PM - 2:50PM

**Location:** BLOC 628

**Speaker:** Thomas Sinclair, Purdue University

**Title:** *(Colloquium Talk) Product rigidity results for group von Neumann algebras*

**Abstract:**Given a locally compact second countable group G, the group von Neumann algebra L(G) is the algebra associated to the invariant subspace decomposition of the left regular representation. It is a natural, and quite difficult, question to address how much of the group structure is recoverable from L(G). That is if two groups have isomorphic group von Neumann algebras what algebraic structure do the groups have in common? In the case of infinite discrete groups, we will explain how if G is a direct product of "indecomposable" groups, such as nonabelian free groups or nonelementary hyperbolic groups, then the product structure can be fully recovered from L(G). This is joint work with Ionut Chifan and Rolando de Santiago.

## Groups and Dynamics Seminar

**Time:** 3:00PM - 4:00PM

**Location:** BLOC 220

**Speaker:** Constantine Medynets, US Naval Academy

**Title:** *Characters of Countable Groups and Ergodic Properties of Their Actions*

**Abstract:**In the 1980s Vershik observed that given an extreme character chi -- satisfying certain conditions -- of the infinite symmetric group S(N) there is an ergodic action of S(N) on a standard measure (X,mu) such that chi(g)=mu(Fix(g)), where Fix(g) is the set of fixed points of the group element g. In this talk, we will discuss two classes of groups where extreme characters can be uniquely described as measures of fixed points of ergodic actions similarly to Vershik’s construction above. We will discuss the class of Higman-Thompson’s groups and the class of AF full groups associated with simple Bratteli diagrams. Note that in view of the Gelfand-Naimark-Segal construction the classification of characters is equivalent to the classification of the finite type von Neumann algebra representations of the group in question.

## First Year Graduate Student Seminar

**Time:** 5:30PM - 6:30PM

**Location:** BLOC 628

**Speaker:** Student Panel

**Title:** *Panel discussion on choosing an advisor*