Seminars & Events for 2010-2011

December 9, 2010
4:30pm - 6:30pm
Gromov's knot distortion
Topology Seminar

Gromov defined the distortion of an embedding of $S^1$ into $R^3$ and asked whether every knot could be embedded with distortion less than 100.  There are (many) wild embeddings of $S^1$ into $R^3$ with finite distortion, and this is one reason why bounding the distortion of a given knot class is hard.  I will show how to give a nontrivial lower bound on the distortion of torus knots.  I will a

Speaker: John Pardon, Princeton University
Location:
Fine Hall 314
December 9, 2010
4:30pm - 6:30pm
Parahoric subgroups and supercuspidal representations of $p$-adic groups
Princeton University/IAS Number Theory Seminar

This is a report on some joint work with Mark Reeder and Jiu-Kang Yu. I will review the theory of parahoric subgroups and consider the induced representation of a one-dimensional character of the pro-unipotent radical. A surprising fact is that this induced representation can (in certain situations) have finite length.

Speaker: Benedict Gross, Harvard University
Location:
IAS Room S-101
December 10, 2010
3:30pm - 4:30pm
Metric flips with Calabi symmetry
Differential Geometry & Geometric Analysis Seminar

I will discuss the metric behavior of the Kahler-Ricci flow on $\mathbb{P}(\mathcal{O}_{\mathbb{P}^n} \oplus \mathcal{O}_{\mathbb{P}^n}(-1)^{\oplus (m+1)})$, assuming that the initial metric satisfies the symmetry defined by Calabi. I will describe the Gromov-Hausdorff limit of the flow as time approaches the singular time and how the Kahler-Ricci flow can be continued.

Speaker: Yuan Yuan, Johns Hopkins University
Location:
Fine Hall 314
December 10, 2010
4:30pm - 6:30pm
Initial time singularities for mean curvature flow
Differential Geometry & Geometric Analysis Seminar
Speaker: Tom Ilmanen, ETH Zürich
Location:
Fine Hall 314
December 13, 2010
4:00pm - 6:00pm
Reformulation of the Covering and Quantizer Problems as Ground States of Interacting Particles
PACM/Applied Mathematics Colloquium

I reformulate the covering and quantizer problems, well-known problems in discrete geometry, as the determination of the ground states of interacting particles in d-dimensional Euclidean space that generally involve single-body, two-body, three-body, and higher-body interactions.

Speaker: Sal Torquato, Princeton University
Location:
Fine Hall 214
December 14, 2010
10:00am - 12:00pm
Concrete mathematical incompleteness
Discrete Mathematics Seminar

An unprovable theorem is a theorem about basic mathematical objects that can only be proved using more than the usual axioms for mathematics (ZFC = Zermelo Frankel set theory with the Axiom of Choice) — and that has been proved using standard extensions of ZFC generally adopted in the mathematical logic community.

Speaker: Harvey Friedman, Columbia University
Location:
Fine Hall 224
December 14, 2010
4:30pm - 6:30pm
Geometric methods for nonlinear quantum many-body systems
Mathematical Physics Seminar

Geometric techniques have played an important role in the seventies, for the study of the spectrum of many-body Schrödinger operators. In this talk I will present a formalism which also allows to study nonlinear systems.

Speaker: Mathieu Lewin, Universite de Cergy-Pointoise
Location:
December 14, 2010
4:30pm - 6:30pm
Restriction varieties and geometric branching rules
Algebraic Geometry Seminar

In representation theory, a branching rule describes the decomposition of the restriction of an irreducible representation to a subgroup. Let $i: F' \rightarrow F$ be the inclusion of a homogeneous variety in another homogeneous variety. The geometric analogue of the branching problem asks to calculate the induced map in cohomology in terms of the Schubert bases of $F$ and $F'$.

Speaker: Izzet Coskun, University of Illinois at Chicago (UIC)
Location:
Fine Hall 322
December 16, 2010
2:30pm - 4:30pm
Choice numbers and coloring numbers - the infinite case
Discrete Mathematics Seminar

The choice number or list-chromatic number $\chi_\ell(G)$ of a graph $G=(V,E)$ is the minimum $k$ such that for every assignment of a list $s(v)$ of $k$ colors to each $v\in V$ there exists a proper coloring $c$ of $V$ that colors each $v$ by a color from $s(v)$.

Speaker: Menachem Kojman, Ben Gurion University and IAS
Location:
Fine Hall 224
December 16, 2010
4:30pm - 6:30pm
Holomorphic Pairs of Pants in Mapping Tori
Topology Seminar

We consider invariants of mapping tori of symplectomorphisms of a symplectic surface S, such as symplectic field theory, contact homology, and periodic Floer homology, for the standard stable Hamiltonian structure on the mapping torus. These invariants involve counts of holomorphic curves in R times the mapping torus.

Speaker: Andy Cotton-Clay, Harvard University
Location:
Fine Hall 314
December 16, 2010
4:30pm - 6:30pm
Weyl's sums for roots of quadratic congruences
Princeton University/IAS Number Theory Seminar

It is known that the roots of congruences for a fixed irreducible quadratic polynomial are equidistributed. This statement translates to getting cancellation in the corresponding sum of Weyl's sums. In a recent work by W. Duke, J. Friedlander and H. Iwaniec we succeeded to get cancellation (so also the equidistribution) in very short sums of Weyl's sums relatively to the discriminant.

Speaker: Henryk Iwaniec, Rutgers University
Location:
Fine Hall 214
February 3, 2011
4:30pm - 6:30pm
Filtering smooth concordance classes of topologically slice knots
Topology Seminar

Cochran, Orr, and Teichner introduced the n-solvable filtration of the knot concordance group, which has given a framework for recent advances in the study of knot concordance. However, it fails to detect anything about topologically slice knots, denoted T.

Speaker: Paul Horn, Columbia University
Location:
Fine Hall 314
February 7, 2011
4:00pm - 6:00pm
High-dimensional reservoir neural dynamics: rules and rewards
PACM/Applied Mathematics Colloquium

Neural activity recorded in behaving animals is highly variable and heterogeneous, which is especially true for neurons in the prefrontal cortex (PFC), the so called 'CEO of the brain' of central importance to many cognitive functions. In this talk, I will present a reservoir-type model of randomly connected neurons to account for the diversity of neural signals in the prefrontal cortex.

Speaker: Xiao-Jing Wang, Yale University
Location:
Fine Hall 214
February 9, 2011
4:30pm - 6:30pm
Multiple mixing and short polynomials
Department Colloquium

In dynamical systems the notion of multiple mixing seems to strengthen that of mixing for an action n a probability space.

Speaker: David Masser, University of Basel, Switzerland
Location:
Fine Hall 314
February 10, 2011
2:00pm - 4:00pm
Discrete Schrödinger operators with periodic and almost periodic potentials
Ergodic Theory & Statistical Mechanics

The first half of the talk will be a survey; I will start from general facts about discrete Schrödinger operators with periodic potentials, and then discuss operators with almost periodic potentials, focusing on the almost Mathieu operator.

Speaker: Mira Shamus, IAS
Location:
Fine Hall 801
February 10, 2011
2:30pm - 4:30pm
Phase Transitions of Achlioptas Processes
Discrete Mathematics Seminar

Achlioptas processes are a class of modifications of the Erdős–Rényi random graph. At each step of an Achlioptas process we add one of two randomly selected edges to the graph according to a fixed rule.

Speaker: Will Perkins, New York University
Location:
Fine Hall 224
February 10, 2011
4:30pm - 6:30pm
Bordered Floer homology and the contact category
Topology Seminar

Bordered Heegaard Floer homology is a verison of Heegaard Floer homology for 3-manifolds with boundary, developed by Lipshitz, Ozsvath, and Thurston. A key component of the theory is a DG-algebra associated to a parametrized surface $F$.

Speaker: Rumen Zarev, Columbia University
Location:
Fine Hall 314
February 10, 2011
4:30pm - 6:30pm
Impossible intersections for elliptic curves
Princeton University/IAS Number Theory Seminar

We proved with Umberto Zannier that there are at most finitely many complex numbers $\lambda \neq {0,1}$ such that two points on the Legendre elliptic curve $y^2 = x(x-1)(x-\lambda)$ with coordinates $x=2$ and $x=3$ both have finite order. However we still do not know how to find these $\lambda$ effectively (there are probably none).

Speaker: David Masser, University of Basel, Switzerland
Location:
Fine Hall 214
February 11, 2011
3:00pm - 5:00pm
The logarithmic singularities of the Green functions of the conformal powers of the Laplacian
Differential Geometry & Geometric Analysis Seminar

Green functions play an important role in conformal geometry. In this talk, we shall explain how to compute explicitly the logarithmic singularities of the Green kernels of the conformal powers of the Laplacian, including the Yamabe and Paneitz operators. The results are formulated in terms of explicit conformal invariants arising from the ambient metric of Fefferman-Graham.

Speaker: Raphael Ponge, University of Tokyo
Location:
Fine Hall 314
February 14, 2011
4:00pm - 6:00pm
A few computational and applied math problems in density functional theory related calculations
PACM/Applied Mathematics Colloquium

Density functional theory (DFT) has become the most widely used quantum mechanical method in material science simulations. Due to the change of computer architectures, and the corresponding change in the scope of problems amenable by the DFT method, the algorithms used in the DFT calculations are also changing.

Speaker: Lin-Wang Wang, Lawrence Berkeley National Laboratory
Location:
Fine Hall 214