2014
Mar
20

# Steven Zeldich

2:30pm to 3:30pm

Edmond J. Safra Campus The Hebrew University of Jerusalem

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2014
Mar
20

2:30pm to 3:30pm

2015
Oct
22

2:30pm to 3:30pm

Title: Counting points and counting representations

Abstract:

I will talk about the following questions:

1) Given a system of polynomial equations with integer coefficients, how many solutions does it have in the ring Z/N?

2) Given a polynomial map f:R^a-->R^b and a smooth, compactly supported measure m on R^a, does the push-forward of m by f have bounded density?

3) Given a lattice in a higher rank Lie group (say, SL(n,Z) for n>2). How many d-dimensional representations does it have?

Abstract:

I will talk about the following questions:

1) Given a system of polynomial equations with integer coefficients, how many solutions does it have in the ring Z/N?

2) Given a polynomial map f:R^a-->R^b and a smooth, compactly supported measure m on R^a, does the push-forward of m by f have bounded density?

3) Given a lattice in a higher rank Lie group (say, SL(n,Z) for n>2). How many d-dimensional representations does it have?

2014
May
22

2:30pm to 3:30pm

2014
Jan
16

2:30pm to 3:30pm

2014
Feb
27

2:30pm to 3:30pm

2013
Nov
14

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.

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.

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.

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.

2015
Dec
17

12:00pm to 1:00pm

Einstein 110

Consider a sequence of random walks on $\mathbb{Z}/p\mathbb{Z}$ with symmetric generating sets $A= A(p)$. I will describe known and new results regarding the mixing time and cut-off. For instance, if the sequence $|A(p)|$ is bounded then the cut-off phenomenon does not occur, and more precisely I give a lower bound on the size of the cut-off window in terms of $|A(p)|$. A natural conjecture from random walk on a graph is that the total variation mixing time is bounded by maximum degree times diameter squared.

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