Colloquium, Academic Year 2013-2014
Tea at 3:30 pm in 1425 Stevenson Center
September 5, 2013 | Welcome event, no colloquium |
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September 12, 2013 | Non-asymptotic approach in random matrix theory Random matrix theory studies the asymptotics of the spectral distributions of families of random matrices, as the sizes of the matrices tend to infinity. Derivation of such asymptotics frequently requires analyzing the spectral properties of random matrices of a large fixed size, especially of their singular values. We will discuss several recent results in this area concerning matrices with independent entries, as well as random unitary and orthogonal perturbations of a fixed matrix. We will also show an application of the non-asymptotic random matrix theory to estimating the permanent of a deterministic matrix. Contact person: Alex Powell |
September 26, 2013 | A survey of algebraic geometry and model theory for free and hyperbolic groups. I will survey results of Kharlampovich--Miasnikov and Sela on first-order theories of free and hyperbolic groups. I will show that in the presence of ``negative curvature'' in groups, there exists a robust algebraic geometry and the principal Tarski-type problems are decidable. In particular, there is an algorithm for the elimination of quantifiers (to boolean combinations of AE-formulas). I will also give a description of definable sets in free and hyperbolic groups (joint result with Miasnikov). This solves Malcev's problem from 1965. Contact person: Denis Osin |
October 3, 2013 | The stable coefficients of the Jones polynomial of a link The Jones polynomial of a link is a finite collection of integers placed at different degrees. We propose a structure theorem for the (stable) coefficients of an alternating link in terms of a flag algebra of graphs, verify it for the first 4 coefficients and present further experimental evidence for the next two. This leads to natural and open questions about categorification of alternating links, and to questions on the structure of flag algebras. Joint work with Thao Vuong and Sergey Norin. Contact person: Vaughan Jones |
October 10, 2013 | Fall break |
October 15, 2013 | Weakly commensurable groups The notion of weak commensurability (of Zariski-dense subgroups of semi-simple algebraic groups) was introduced in the ongoing joint work with Gopal Prasad on length-commensurable and isospectral locally symmetric spaces. We were able to determine when two arithmetic subgroups are weakly commensurable. This led to various geometric results, some of which are related to the famous question "Can one hear the shape of a drum?" Contact person: Denis Osin |
October 17, 2013 | Faculty meeting, no colloquium |
October 24, 2013 | About topological expansions Maps are connected graphs which are properly embedded into a surface, their genus is the minimal genus of such a surface. Matrix integrals have been shown to be related with the enumeration of maps since the seventies, after the work of Hooft and Brezin-Itzykson-Parisi and Zuber. This is the so-called topological expansion. Such an expansion has been used in many fields of physics and mathematics. In this talk, we shall describe this correspondence, discuss some applications and some generalizations. Contact person: Dietmar Bisch |
November 7, 2013 | Topological data analysis is the idea that high dimensional large data sets can sometimes be more effectively understood by looking for an underlying geometric structure which can then be exploited for the purposes of analysis. (It is one of the themes of this year's special year at IMA.) In this talk I will try to explain some interesting problems that arise from this perspective: some good news and some bad news and then some more good news. Contact person: John Ratcliffe |
November 11, 2013 | Combinatorics and complexity of Kronecker coefficients Contact person: Denis Osin |
November 14, 2013 | Seeing geometry in certain kinds of modules I'll begin by explaining a very primitive notion of non-positive curved space called a CAT(0) space. It's so simple that it can be understood by anyone who knows what a metric space is and who likes geometry. My CAT(0) space M will come with a group G of isometries of M. This leads to the notion of the limit set of this action of G. Much more interesting, and the focus of my talk, is a set of special limit points called the "horospherical limit set". After a short discussion of what this means in general I'll explain how it shows up in several parts of real mathematics: Fuchsian and Kleinian groups, discrete subgroups of Lie groups, and tropical geometry, as well as, more generally, the issue of trying to see geometry in the structure of ZG-modules. This is a colloquium talk arranged around my joint work with Robert Bieri. Contact person: Mike Mihalik |
November 21, 2013 | Pushing Polynomial Reproducing Kernels to Their Nonpolynomial Limits Polynomial reproducing kernels are an essential tool in analyzing orthogonal polynomials and orthogonal expansions. They also play a key role in universality limits for random matrices. We discuss these connections. Moreover, we analyze how such the limiting form of these polynomial kernels becomes the sinc kernel for Paley-Wiener spaces. Contact person: Edward Saff |
December 3, 2013 | Special lecture |
January 9, 2014 | Special lecture |
January 13, 2014 | Special lecture |
January 14, 2014 | Special lecture |
January 16, 2014 | Special lecture |
January 20, 2014 | Special lecture |
January 21, 2014 | Faculty meeting, no colloquium |
February 6, 2014 | The triangulation conjecture Contact person: Bruce Hughes |
February 13, 2014 | Geodesics on diffeomorphism groups and their subgroups. In the past fifty years certain problems in both classical and modern physics have been studied from the perspective of geodesics on groups. This began with the work of V. I. Arnold on the study of motions of a rigid body and of incompressible fluids, the former using the group SO(3) and the latter using the group of diffeomorphisms of a region which preserve its volume element (volumorphisms). Subsequently, this work has been expanded to include diffeomorphisms that preserve a symplectic form, a contact form, and a contact structure (respectively, symplectoporphisms, quantomorphisms and contactomorphisms). We shall discuss the analysis required to find the geodesics in these situations. It will involve solving ODE's on infinite dimensional spaces an some PDE techniques as well. Contact person: Gieri Simonett, Marcelo Disconzi |
February 20, 2014 | Finitely based algebras A law is a universally quantified equation, such as the associative law or the commutative law. I intend to talk about the problem of determining which algebras have a finite basis for their laws. Most of my talk will be about the laws of finite algebras. Contact person: Ralph McKenzie |
February 27, 2014 | Boundary theory and simplicity of the Lyapunov spectrum Consider products of matrices that are chosen using some ergodic stationary random process on $G=SL_d(R)$, e.g. a random walk on $G$. The Multiplicative Ergodic Theorem (Oseledets) asserts that the asymptotically such products behave as powers $\Lambda^n$ of a fixed diagonal matrix $\Lambda$, called the Lyapunov spectrum of the system. The spectrum $\Lambda$ depends on the system in a mysterious way, and is almost never known explicitly. The best understood case is that of random walks, where by the work of Furstenberg, Guivarc'h-Raugi, and Gol'dsheid-Margulis we know that the spectrum is simple (i.e. all values are distinct) provided the random walk is not trapped in a proper algebraic subgroup. Recently, Avila and Viana proved a conjecture of Kontsevich-Zorich that asserts simplicity of the Lyapunov spectrum for another system related to Teichmuller flow. In the talk we shall describe an approach to proving simplicity of the spectrum based on ideas from boundary theory that were developed to prove rigidity of lattices. Based on joint work with Uri Bader. Contact person: Jesse Peterson |
March 6, 2014 | Spring break, no colloquium |
March 13, 2014 | Free subgroups of three-manifold groups Contact person: Mark Sapir |
March 20, 2014 | Faculty meeting, no colloquium |
March 27, 2014 | Interpolating between classical and dynamical dimension Motivated by a suggestion of Gromov, Lindenstrauss and Weiss developed a dimension theory for topological dynamical systems called the mean dimension. While it functions well for minimal systems, the theory breaks down as periodic points become more prevalent. In this talk I'll introduce a notion of dimension using modules over C*-algebras which aims to repair these defects while maintaining the character of the mean dimension for minimal systems. Contact person: Jesse Peterson |
April 3, 2014 | Transverse Geometry of Tiling Spaces The tiling space of a given tiling will be described first on the example of the Fibonacci sequence and of the octagonal tiling. A more formal defintion will be provided then. It will be shown that for the class of tilings that are repetitive, aperiodic with finite local complexity the tiling space is a Cantor set. Hence a Geometry can only be described in the context of Noncommutative approach, through "spectral triples". This concept will be defined and exemplified in the case of Riemannian manifolds. Then the Palmer-Pearson spectral triple will be described in detail. At last the construction of the Pearson operator, the Cantor analog of the Laplace-Beltrami operator will be defined. Its spectral properties will be quickly described. Contact person: Arnaud Brothier |
April 10, 2014 | Poincaré inequalities and metric embeddings into Banach spaces An expander is an unbounded sequence of finite graphs with very high connectivity, but uniformly bounded degree. These graphs have applications ranging from computer sciences to non-commutative geometry. However, they are not easy to construct and the first examples were actually obtained by random methods. More recently, explicit examples were produced in the context of group theory. Gromov observed that among its various strange properties, an expander cannot be "coarsely" embedded into a Hilbert space, and it was open for some time whether ''containing an expander'' was the only obstruction. After recalling the relevant basic notions and results, we shall expose recent development about this question. Contact person: Denis Osin |
April 15, 2014 | The relativistic Navier-Stokes and Einstein's equations In this talk, we shall discuss the problem of formulating a relativistic theory of viscous fluids. After a brief introduction to the relevant concepts of General Relativity and the Einstein equations, we shall explain the origins of the problem and the known difficulties in addressing it. We finish with some of our recent results, which point toward a resolution of the problem. The talk will be accessible to non-specialists, and it will be largely self-contained. Graduate and advanced undergraduate students are encouraged to attend. Contact person: Dietmar Bisch |
April 17, 2014 | Questions of crystallization in Coulomb systems We are interested in systems of points with Coulomb interaction. An instance is the classical Coulomb gas, another is vortices in the Ginzburg-Landau model of superconductivity, where one observes in certain regimes the emergence of densely packed point vortices forming perfect triangular lattice patterns, named Abrikosov lattices in physics. In joint works with Etienne Sandier and with Nicolas Rougerie, we studied both systems and derived a "Coulombian renormalized energy". I will present it, examine the question of its minimization and its link with the Abrikosov lattice and weighted Fekete points. I will describe its relation with the statistical mechanics models mentioned above and show how it leads to expecting crystallisation in the low temperature limit. Contact person: Ed Saff |
Colloquium Chair (2013-2014): Denis Osin