2014
Feb
20

# Gil Kalai

2:30pm to 3:30pm

2014
Feb
20

2:30pm to 3:30pm

2017
Jan
19

4:00pm to 5:00pm

Manchester building room 2

Abstract - Equidistribution problems, originating from the classical works of Kronecker, Hardy and Weyl about equidistribution of sequences mod 1, are of major interest in modern number theory.
We will discuss how some of those problems relate to unipotent flows and present a conjecture by Margulis, Sarnak and Shah regarding an analogue of those results for the case of the horocyclic flow over a Riemann surface. Moreover, we provide evidence towards this conjecture by bounding from above the Hausdorff dimension of the set of points which do not equidistribute.

2014
Jun
12

2:30pm to 3:30pm

2014
Mar
20

2:30pm to 3:30pm

2017
Sep
14

2:30pm to 3:30pm

IIAS hall, Hebrew University Jerusalem

I will give introduction to sofic groups and discuss a possible strategy towards finding a non-sofic group. I will show that if the Higman group were sofic, there would be a map from Z/pZ to itself, locally like an exponential map, satisfying a rather strong recurrence property. The approach to (non)-soficity is based on the study of sofic representations of amenable subgroups of a sofic group. This is joint work with Harald Helfgott.

2016
Jan
10

4:00pm to 5:00pm

Ross 70A

Abstract: The original construction uses the theory of pseudo-holomorphic curves. In this lecture, I will describe an explicit combinatorial algorithm for computing knot Floer homology in terms of grid diagrams. In this lecture, I will describe joint work with Ciprian Manolescu, Sucharit Sarkar, Zoltan Szabo, and Dylan Thurston.

2016
Jan
11

12:00pm to 1:00pm

Ross 70A

Abstract: Bordered Floer homology is an invariant for three-manifolds with boundary, defined in collaboration with Robert Lipshitz and Dylan Thurston. The invariant associates a DG algebra to a parameterized surface, and a module over that algebra to a three-manifold with boundary. I will explain how methods from bordered Floer homology can be used to give a tidy description of knot Floer homology. This is joint work with Zoltan Szabo.

2017
Jun
21

2017
Sep
12

12:00pm to 1:00pm

Ross Building Room 70A

We ask whether every homologically trivial cyclic action on a symplectic four-manifold extend to a Hamiltonian circle action. By a cyclic action we mean an action of a cyclic group of finite order; it is homologically trivial if it induces the identity map on homology. We assume that the manifold is closed and connected. In the talk, I will give an example of a homologically trivial symplectic cyclic action on a four-manifold that admits Hamiltonian circle actions, and show that is does not extend to a Hamiltonian circle action.

2016
Jun
15

2:00pm to 3:35pm

Ross building, Hebrew University (Seminar Room 70A)

Abstract:
Derived algebraic geometry is a nonlinear analogue of homological algebra, in which one keeps track of syzygies among the relations among the defining equations of a variety, and higher analogues. It has important applications to intersection theory and enumerative geometry.

2017
May
23

1:00pm to 1:50pm

Ross A70.

Abstract: Let \Sigma be a compact connected oriented 2-manifold of genus g , and let p be a point on \Sigma. We define a space S_g(t) consisting of certain irreducible representations of the fundamental group of \Sigma - { p } , modulo conjugation by SU(N).

2017
Aug
09

12:00pm to 1:00pm

Room 70A, Ross Building, Jerusalem, Israel

Knot Floer homology is an invariant for knots in the three-sphere defined using methods from symplectic geometry. I will describe a new algebraic formulation of this invariant which leads to a reasonably efficient computation of these invariants. This is joint work with Zoltan Szabo.

2015
Dec
22

2:00pm to 3:00pm

Math 209 (Manchester building)

We consider (complex) Gaussian analytic functions on a horizontal strip, whose distribution is invariant with respect to horizontal shifts (i.e., "stationary"). Let N(T) be the number of zeroes in [0,T] x [a,b]. We present an extension of a result by Wiener, concerning the existence and characterization of the limit N(T)/T as T approaches infinity, as well as characterize the growth of the variance of N(T).

2015
Nov
05

9:45am to 11:00am

Manchester building, Hebrew University of Jerusalem, (Room 209)

Title: Arithmetic of Double Torus Quotients and the Distribution of Periodic Torus Orbits
Abstract:
In this talk I will describe some new arithmetic invariants for pairs of torus orbits on inner forms of PGLn and SLn. These invariants allow us to significantly strengthen results towards the equidistribution of packets of periodic torus orbits on higher rank S-arithmetic quotients. An important aspect of our method is that it applies to packets of periodic orbits of maximal tori which are only partially split.

2016
Apr
10

4:00pm to 5:00pm

Lecture hall 2

A signature of chaotic behavior in dynamical systems is sensitive dependence on initial conditions, and Lyapunov exponents measure the rates at which nearby orbits diverge. One might expect that geometric expansion or stretching in a map would lead to positive Lyapunov exponents. This, however, is very difficult to prove - except for maps with invariant cones (or a priori separation of expanding and contracting directions).