2014 Jan 02

2:30pm to 3:30pm

2014 Mar 13

2:30pm to 3:30pm

2013 Oct 31

2:30pm to 3:30pm

2017 Jun 08

# Wolf Prize Lecture - Rick Schoen (Stanford): The geometry of eigenvalue extremal problems

11:00am to 12:00pm

## Location:

Levin building, lecture hall 8
Title: “The geometry of eigenvalue extremal problems” Abstract: When we choose a metric on a manifold we determine the spectrum of the Laplace operator. Thus an eigenvalue may be considered as a functional on the space of metrics. For example the first eigenvalue would be the fundamental vibrational frequency. In some cases the normalized eigenvalues are bounded independent of the metric. In such cases it makes sense to attempt to find critical points in the space of metrics. In this talk we will survey two cases in which progress has been made focusing primarily on the case of surfaces with
2013 Dec 12

2:30pm to 3:30pm

2014 Feb 20

2:30pm to 3:30pm

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 10

# Zabrodsky lecture series: Peter Ozsváth (Princeton) "Computational aspects of knot Floer homology"

4:00pm to 5:00pm

## Location:

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.
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.
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 Jun 21

2:00pm to 2:50pm

Ross 70A.
Abstract:
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.
2016 Jun 15

# Topology & geometry, Ezra Getzler (Northwestern University), "The derived Maurer-Cartan locus"

2:00pm to 3:35pm

## Location:

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

# Topology & Geometry Seminar: Adina Gamse (University of Toronto), "Vanishing relations in the cohomology of the moduli space of parabolic bundles".

1:00pm to 1:50pm

## Location:

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).
2015 Dec 08

# Dynamics & probability: Brandon Seward (HUJI): "Positive entropy actions of countable groups factor onto Bernoulli shifts"

2:00pm to 3:00pm

## Location:

Manchester building, Hebrew University of Jerusalem, (Room 209)
Title: Positive entropy actions of countable groups factor onto Bernoulli shifts Abstract: I will prove that if a free ergodic action of a countable group has positive Rokhlin entropy (or, less generally, positive sofic entropy) then it factors onto all Bernoulli shifts of lesser or equal entropy. This extends to all countable groups the well-known Sinai factor theorem from classical entropy theory. As an application, I will show that for a large class of non-amenable groups, every positive entropy free ergodic action satisfies the measurable von Neumann conjecture.