Abstracts
Week of November 3, 2024
| Tea | Cookies |
3:30pm -
KT 8th Floor Lounge
|
Please join us for pre-seminar Tea |
| Geometry, Symmetry and Physics | Higher Genus Gromov–Witten theory of Smooth Calabi–Yau Threefolds in Weighted P^4 |
4:30pm -
KT 801
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The Yamaguchi–Yau finite generation conjecture predicts that the higher-genus Gromov–Witten potentials of compact Calabi–Yau threefolds are polynomials in a finite number of generators. In this talk, I will outline a recent approach to apply Givental’s quantization formalism to the Gromov–Witten theory of Calabi–Yau threefolds and explain a proof of this conjecture for smooth Calabi–Yau hypersurfaces in P(1, 1, 1, 1, 2), P(1, 1, 1, 1, 4), and P(1, 1, 1, 2, 5). |
| Tea | Cookies |
3:30pm -
KT 8th Floor Lounge
|
Please join us for pre-seminar Tea |
| Analysis | Mathematical theory of internal waves |
4:00pm -
KT 207
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Internal waves are a central topic in oceanography and the theory of rotating fluids. They are gravity waves in density-stratified fluids. In a two-dimensional aquarium, the velocity of linear internal waves can concentrate on certain attractors. Locations of internal wave attractors are related to periodic orbits of homeomorphisms of the circle, given by a nonlinear “chess billiard” dynamical system. This relation provides a surprising “quantum–classical correspondence” in fluid dynamics. In this talk, I will explain connections between homeomorphisms of circles, spectral theory, and internal wave dynamics. This talk is based on joint work with Semyon Dyatlov and Maciej Zworski. |
| Applied Mathematics | Efficient, Robust and Agnostic Generative Modeling with Group Symmetry and Regularized Divergences |
2:30pm -
LOM 214
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In this talk, I will discuss our recent theoretical advancements in generative modeling. The first part of the presentation will focus on learning distributions with symmetry. I will introduce results on the sample complexity of empirical estimations of probability divergences for group-invariant distributions, and present performance guarantees for GANs and score-based generative models that incorporate symmetry. Notably, I will offer the first quantitative comparison between data augmentation and directly embedding symmetry into models, highlighting the latter as a more fundamental approach for efficient learning. These findings underscore how incorporating symmetry into generative models can significantly enhance learning efficiency, particularly in data-limited scenarios. The second part will cover $\alpha$-divergences with Wasserstein-1 regularization. These divergences can be interpreted as $\alpha$-divergences constrained to Lipschitz test functions in their variational form. I will demonstrate how generative learning can be made agnostic to assumptions about target distributions, including those with heavy tails or low-dimensional and fractal supports, through the use of these divergences as objective functionals. I will outline the conditions for the finiteness of these divergences under minimal assumptions on the target distribution along with the gradient flow formulation associated with them. This framework provides guarantees for various machine learning algorithms that optimize over this class of divergences. |
| Tea | Cookies |
3:30pm -
KT 8th Floor Lounge
|
Please join us for pre-Colloquium Tea |
| Colloquium | Probabilistic scaling, propagation of randomness and invariant Gibbs measures |
4:00pm -
KT 205
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In this talk, we will start by describing how classical tools from probability offer a robust framework to understand the dynamics of waves via appropriate ensembles on phase space rather than particular microscopic dynamical trajectories. We will continue by explaining the fundamental shift in paradigm that arises from the “correct” scaling in this context and how it opened the door to unveil the random structures of nonlinear waves that live on high frequencies and fine scales as they propagate. We will then discuss how these ideas broke the logjam in the study of the Gibbs measures associated to nonlinear Schrödinger equations in the context of equilibrium statistical mechanics and of the hyperbolic $\Phi^4_3$ model in the context of constructive quantum field theory. We will end with some open challenges about the long-time propagation of randomness and out-of-equilibrium dynamics. |
| Tea | Cookies |
3:30pm -
KT 8th Floor Lounge
|
Please join us for pre-seminar Tea |
| Analysis | Variable coefficient Lp local smoothing |
4:00pm -
Zoom
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I will discuss some recent work concerning variable coefficient extensions of Lp local smoothing estimates for the Schrodinger propagator. This can be thought of as a counterpart to a classical oscillatory integral operator bound of Bourgain (1991). Whilst Bourgain’s result relies on studying Kakeya sets of curves, our Lp local smoothing result relies on studying Nikodym sets of curves. An important observation of Wisewell (2005) is that the Nikodym theory is surprisingly different from the Kakeya theory. Our work aims to further investigate and exploit these differences. |
| Quantum Topology and Field Theory | Skein traces from curve counting |
4:30pm -
KT 101
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I will describe a joint project with Tobias Ekholm, Pietro Longhi, and Vivek Shende constructing a map from the HOMFLYPT skein module of a 3-manifold M to that of its branched cover arising from the projection of a Lagrangian 3-manifold L in the cotangent bundle of M. The map is defined by counting holomorphic curves and is a vast generalization of the quantum UV-IR map of Neitzke and Yan, which is a close cousin of the quantum trace map of Bonahon and Wong. The existence of this map has some interesting consequences in the theory of skein-valued curve counts, and I will discuss some of them if time permits. |
| Friday Morning Seminar | Annular webs and central elements in skein algebras |
10:00am -
KBT 801
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The skein algebra of a surface is spanned by links in the thickened surface, subject to skein relations which diagrammatically encode the data of a quantum group. The multiplication in the algebra is induced by stacking links in the thickened surface. This product is generally noncommutative. When the quantum parameter q is generic, the center of the skein algebra is essentially trivial. However, when q is a root of unity, interesting central elements arise. When the quantum group is quantum SL(2), the work of Bonahon-Wong shows that these central elements can be obtained by a topological operation of threading Chebyshev polynomials along knots. In this talk, I will discuss how these threading operations extend to other kinds of skein theories, including SL(n), Sp(2n), and G_2 webs. I will discuss a method for checking that the elements produced are central in the skein algebra by studying webs in the annulus. Some of these works are joint with Francis Bonahon, Haihan Wu, and an REU group.
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