Two rigid algebras and a heat kernel

Amitai Zernik
Member, School of Mathematics
April 7, 2017
Consider the Fukaya A8 algebra $E$ of $RP^{2m}$ in $CP^{2m}$ (with bulk and equivariant deformations, over the Novikov ring). On the one hand, elementary algebraic considerations show that E admis a rigid cyclic minimal model, whose structure constants encode the associated open Gromov-Witten invariants. On the other hand, in a recent paper another rigid minimal model was computed explicitly, using fixed-point localization for A8 algebras. In this talk I'll discuss these two models and explain how to use the heat kernel on $RP^{2m}$ to relate them.

On Zimmer's conjecture

Sebastian Hurtado-Salazar
University of Chicago
April 6, 2017

The group $\mathrm{SL}_n(\mathbb Z)$ (when $n > 2$) is very rigid, for example, Margulis proved all its linear representations come from representations of $\mathrm{SL}_n(\mathbb R)$ and are as simple as one can imagine. Zimmer's conjecture states that certain "non-linear" representations ( group actions by diffeomorphisms on a closed manifold) come also from simple algebraic constructions.

Basic loci of Shimura varieties

Xuhua He
University of Maryland; von Neumann Fellow, School of Mathematics
April 6, 2017

In mod-$p$ reductions of modular curves, there is a finite set of supersingular points and its open complement corresponding to ordinary elliptic curves. In the study of mod-$p$ reductions of more general Shimura varieties, there is a "Newton stratification" decomposing the reduction into finitely many locally closed subsets, of which exactly one is closed. This closed set is called the basic locus; it recovers the supersingular locus in the classical case of modular curves.

A time-space lower bound for a large class of learning problems

Ran Raz
Princeton University
April 3, 2017

We prove a general time-space lower bound that applies for a large class of learning problems and shows that for every problem in that class, any learning algorithm requires either a memory of quadratic size or an exponential number of samples. As a special case, this gives a new proof for the time-space lower bound for parity learning [R16].

Algebra and geometry of the scattering equations

Peter Goddard
Professor Emeritus, School of Natural Sciences
April 3, 2017
Four years ago, Cachazo, He and Yuan found a system of algebraic equations, now named the "scattering equations", that effectively encoded the kinematics of massless particles in such a way that the scattering amplitudes, the quantities of physical interest, in gauge theories and in gravity could be written as sums of rational functions over their solutions.

Speculations about homological mirror symmetry for affine hypersurfaces

Denis Auroux
University of California, Berkeley; Member, School of Mathematics
March 31, 2017
The wrapped Fukaya category of an algebraic hypersurface $H$ in $(C*)^n$ is conjecturally related via homological mirror symmetry to the derived category of singularities of a toric Calabi-Yau manifold $X$, whose moment polytope is determined by the tropicalization of $H$. (The case of the pair of pants discussed in the first talk is a special case of this construction).

Rigid holomorphic curves are generically super-rigid

Chris Wendl
Humboldt-Universität zu Berlin
March 31, 2017
I will explain the main ideas of a proof that for generic compatible almost complex structures in symplectic manifolds of dimension at least 6, closed embedded J-holomorphic curves of index 0 are always "super-rigid", implying that their multiple covers are never limits of sequences of curves with distinct images. This condition is especially interesting in Calabi-Yau 3-folds, where it follows that the Gromov-Witten invariants can be "localized" and computed in terms of Euler classes of obstruction bundles for a finite set of disjoint embedded curves.

The many forms of rigidity for symplectic embeddings

Felix Schlenk
University of Neuchâtel
March 30, 2017
We look at the following chain of symplectic embedding problems in dimension four. \[E(1, a) \to Z_4(A),\ E(1, a) \to C_4(A),\ E(1, a) \to P(A, ba) (b \in {\mathbb N}_{\geq 2}),\ E(1, a) \to T_4(A).\] Here $E(1, a)$ is a symplectic ellipsoid, $Z_4(A)$ is the symplectic cylinder $D_2(A) \times R_2$, $C_4(A) = D_2(A) \times D_2(A)$ is the cube and $P(A, bA) = D_2(A) \times D_2(bA)$ the polydisc, and $T_4(A) = T_2(A) \times T_2(A)$, where $T_2(A)$ is the 2-torus of area $A$. In each problem we ask for the smallest $A$ for which $E(1, a)$ symplectically embeds.