Events & Seminars

2017 Jan 19

Special colloquium: Asaf Katz (HUJI Perlman prize) "Sparse equidistribution in unipotent flows"

4:00pm to 5:00pm

Location: 

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.
2017 Sep 14

Colloquium: Kate Juschenko (Northwestern University) - "Cycling amenable groups and soficity"

2:30pm to 3:30pm

Location: 

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 11

Zabrodsky lecture series: Peter Ozsváth (Princeton) "Bordered Floer homology"

12:00pm to 1:00pm

Location: 

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 Sep 12

T&G: Liat Kessler (Cornell and Oranim), Extending Homologically trivial symplectic cyclic actions to Hamiltonian circle actions

12:00pm to 1:00pm

Location: 

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.
2017 Aug 09

T&G: Peter Ozsvath (Princeton), Bordered methods in knot Floer homology

12:00pm to 1:00pm

Location: 

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

Dynamics & probability: Naomi Feldheim (Stanford), "New results on zeroes of stationary Gaussian functions"

2:00pm to 3:00pm

Location: 

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

Groups & Dynamics : Ilya Khayutin (HUJI)

9:45am to 11:00am

Location: 

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

Dvoretzky lecture 2: Lai-Sang Young (Courant) "Proving the positivity of Lyapunov exponents"

4:00pm to 5:00pm

Location: 

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).

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