Previous Conferences & Workshops

Apr
13
2022

Arithmetic Groups

Arithmetic and Dynamics on Varieties of Markoff Type
11:00am|Simonyi 101 and Remote Access

The Markoff equation $x^{2} + y^{2} + z^{2}=3xyz$, which arose in his spectacular thesis (1879), is ubiquitous in a tremendous variety of contexts.  After reviewing some of these, we will discuss joint work with Bourgain and Sarnak establishing...

Apr
12
2022

Computer Science/Discrete Mathematics Seminar II

Multi-group fairness, loss minimization and indistinguishability
Parikshit Gopalan
10:30am|Simonyi Hall 101 and Remote Access

Training a predictor to minimize a loss function fixed in advance is the dominant paradigm in machine learning. However, loss minimization by itself might not guarantee desiderata like fairness and accuracy that one could reasonably expect from a...

Apr
11
2022

Joint IAS/Princeton University Symplectic Geometry Seminar

Integral Gromov-Witten invariants and complex derived orbifold bordism
Shaoyun Bai
4:00pm|Simonyi 101 and Remote Access

Because of the presence of non-trivial automorphisms of stable maps, Gromov-Witten invariants of a general symplectic manifold are usually rational-valued. Realizing a proposal of Fukaya-Ono back in the 1990s, I will explain how to construct integer...

Apr
11
2022

Computer Science/Discrete Mathematics Seminar I

The Long Arm of Theoretical Computer Science: A Case Study in Blockchains/Web3
Tim Roughgarden
11:15am|Simonyi 101 and Remote Access

Blockchains that support a general contract layer (e.g., Ethereum) export the functionality of a general-purpose, ownerless, and open-access computer that can enforce property rights for digital data.  How is such functionality implemented?  Using a...

Apr
08
2022

Workshop on Recent developments in incompressible fluid dynamics

An Intermittent Onsager Theorem
Vlad Vicol
10:30am|Simonyi 101 and Remote Access

For any regularity exponent $\beta<\frac 12$, we construct non-conservative weak solutions to the 3D incompressible Euler equations in the class $C^0_t (H^{\beta} \cap L^{\frac{1}{(1-2\beta)}})$.  By interpolation, such solutions belong to $C^0_tB^{s}_{3,\infty}$ for $s$ approaching $\frac 13$ as $\beta$ approaches $\frac 12$.  Hence this result provides a new proof of the flexible side of the Onsager conjecture, which is independent from that of Isett.  Of equal importance is that the intermittent nature of our solutions matches that of turbulent flows, which are observed to possess an $L^2$-based regularity index exceeding $\frac 13$.  The proof employs an intermittent convex integration scheme for the 3D incompressible Euler equations.  We employ a scheme with higher-order Reynolds stresses, which are corrected via a combinatorial placement of intermittent pipe flows of optimal relative intermittency.

Apr
08
2022

Joint IAS/Princeton/Montreal/Paris/Tel-Aviv Symplectic Geometry Zoominar

Lagrangians, symplectomorphisms and zeroes of moment maps
Yann Rollin
9:15am|Remote Access

I will present two constructions of Kähler manifolds, endowed with Hamiltonian torus actions of infinite dimension. In the first example, zeroes of the moment map are related to isotropic maps from a surfaces in $\mathbb{R}^{2n}$. In the second...

Apr
08
2022

Workshop on Recent developments in incompressible fluid dynamics

Non-uniqueness of Leray solutions of the forced Navier-Stokes equations
9:00am|Simonyi 101 and Remote Access

Abstract:In his seminal work, Leray demonstrated the existence of global weak solutions, with nonincreasing energy, to the Navier-Stokes equations in three dimensions. In this talk we exhibit two distinct Leray solutions with zero initial velocity...

Apr
07
2022

Joint IAS/Princeton University Number Theory Seminar

The average size of 3-torsion in class groups of 2-extensions
Robert Lemke Oliver
4:30pm|Remote Access and Fine 214

We determine the average size of the 3-torsion in class groups of $G$-extensions of a number field when $G$ is any transitive 2-group containing a transposition, for example, $D4$.  It follows from the Cohen--Lenstra--Martinet heuristics that the...

Apr
07
2022

Workshop on Recent developments in incompressible fluid dynamics

On the competition between advection and vortex stretching
Jiajie Chen
4:00pm|Simonyi 101 and Remote Access

Abstract: Whether the 3D incompressible Euler equations can develop a finite-time singularity from smooth initial data is an outstanding open problem. The presence of vortex stretching is the primary source of a potential finite-time singularity...