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Week of April 21, 2024

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April 22, 2024
Group Actions, Geometry and Dynamics [3] Rich representations and superrigidity Matthew Stover - Temple University 4:00pm -
KT205
April 24, 2024
Applied Mathematics [4] Quantifying rare and extreme events in PDE systems involving random parameters Georg Stadler - NYU 3:00pm -
LOM 214
April 25, 2024
Analysis [5] Rational solutions to the mKdV equation Giorgo Young - University of Michigan 4:00pm -
KT 201
April 26, 2024
Friday Morning Seminar [6] Schubert Polynomials and the Boson-Fermion Correspondence Sylvester Zhang - University of Minnesota 10:00am -
KT801
Geometry, Symmetry and Physics [7] Higher Virasoro Algebras Brian Williams - Boston University 2:30pm -
KT217

Abstracts

Week of April 21, 2024

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April 22, 2024
Group Actions, Geometry and Dynamics [3] Rich representations and superrigidity 4:00pm -
KT205
This talk will be about joint work with Baldi, Miller, and Ullmo that uses dynamics and/or Hodge theory to study rigidity problems for representations of real and complex hyperbolic lattices, especially those with many properly immersed totally geodesic subspaces (which are among the most well-studied lattices). Very roughly, rich representations are those for which the image of the representation has an action that respects this abundant collection of subgroups in some way, for instance the homomorphism induced by a map f : M -> N where infinitely many properly immersed totally geodesic subspaces of M map into a properly immersed totally geodesic subspace of N. The geometric motivation for defining rich representations has appeared in previous work of several people in several contexts. I will describe settings where we can show that rich representations are superrigid, including some progress toward a question of Siu about whether holomorphic embeddings between higher-dimensional complex hyperbolic manifolds must be totally geodesic.
 
April 24, 2024
Applied Mathematics [4] Quantifying rare and extreme events in PDE systems involving random parameters 3:00pm -
LOM 214

Estimation of tail probabilities in systems that involve uncertain parameters or random forcing is important when these unlikely events have severe consequences. Examples of such events are hurricanes, energy grid blackouts, or failure of engineered systems. After explaining the challenges of estimating rare event probabilities, I will make a connection between extreme event probability estimation and constrained optimization that is established by large deviation theory. The approach leads to practical methods to estimate small probabilities, and a novel class of challenging, large-scale PDE-constrained optimization problems. I will show examples governed by the shallow water equation where one is interested in estimated the probability of large tsunamis on shore, and the randomly forced Navier Stokes equations, where one is interested in the probability of large point strains.

April 25, 2024
Analysis [5] Rational solutions to the mKdV equation 4:00pm -
KT 201

In this talk, I will give a brief overview of the scattering transform for the mKdV equation from the perspective of the Riemann-Hilbert method, and introduce the robust inverse scattering transform. I will describe how we use this perspective to produce rational solutions to the mKdV equation of arbitrary order, already present at low order in the literature. By examining a limiting Riemann Hilbert problem, we also produce rational solutions of infinite order. We realize these solutions as limits of the finite order solutions, and describe some of their asymptotics. This is ongoing and joint work with Deniz Bilman, Elliot Blackstone, and Peter Miller. 

April 26, 2024
Friday Morning Seminar [6] Schubert Polynomials and the Boson-Fermion Correspondence 10:00am -
KT801

The Boson-Fermion correspondence has found connection to symmetric functions through its application for deriving soliton solutions of the KP equations. In this framework, the space of Young diagrams is the Fermionic Fock space, while the ring of symmetric functions is the Bosonic Fock space. Then the (second part of) BF correspondence asserts that the map sending a partition to its Schur function forms an isomorphism as H-modules, with H being the Heisenberg algebra. In this talk, we give a generalization of this correspondence into the context of Schubert calculus, wherein the space of infinite permutations plays the role of the fermionic space, and the ring of back-stable symmetric functions represents the bosonic space.

Geometry, Symmetry and Physics [7] Higher Virasoro Algebras 2:30pm -
KT217

I will propose two classes of algebras which are generalizations/enhancements of the Virasoro algebra in conformal field theory. The first class of examples exists in any dimension, and like the Virasoro Lie algebra, are built from central extensions of vector fields. The second example exists only in dimension three and appears as an enhancement of conformal symmetry in the famous AGT correspondence.

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Links
[1] https://calendar.math.yale.edu/list/calendar/grid/week/2024-W16 [2] https://calendar.math.yale.edu/list/calendar/grid/week/2024-W18 [3] https://calendar.math.yale.edu/seminars/group-actions-geometry-and-dynamics [4] https://calendar.math.yale.edu/seminars/applied-mathematics [5] https://calendar.math.yale.edu/seminars/analysis [6] https://calendar.math.yale.edu/seminars/friday-morning-seminar [7] https://calendar.math.yale.edu/seminars/geometry-symmetry-and-physics [8] https://calendar.math.yale.edu/list/calendar/grid/week/abstract/2024-W16 [9] https://calendar.math.yale.edu/list/calendar/grid/week/abstract/2024-W18