Recently Added

Fitting manifolds to data.

Charlie Fefferman
Princeton University
April 7, 2018

The problems come in two flavors.
 
Extrinsic Flavor: Given a point cloud in R^N sampled from an unknown probability density, how can we decide whether that probability density is concentrated near a low-dimensional manifold M with reasonable geometry? If such an M exists, how can we find it? (Joint work with S. Mitter and H. Narayanan)
 

Exceptional holonomy and related geometric structures: Examples and moduli theory.

Simon Donaldson
Stonybrook University
April 4, 2018

We will discuss the constructions of compact manifolds with exceptional holonomy (in fact, holonomy $G_{2}$),  due to Joyce and Kovalev.  These both use “gluing constructions”. The first involves de-singularising quotient spaces and the second constructs a 7-manifold from “building blocks” derived from Fano threefolds.  We will explain how the local moduli theory is determined by a period map and discuss connections between the global moduli problem and Riemannian convergence theory (for manifolds with bounded Ricci curvature).

Summation formulae and speculations on period integrals attached to triples of automorphic representations

Jayce Getz
Duke University; Member, School of Mathematics
March 27, 2018

Braverman and Kazhdan have conjectured the existence of summation formulae that are essentially equivalent to the analytic continuation and functional equation of Langlands L-functions in great generality. Motivated by their conjectures and related conjectures of L. Lafforgue, Ngo, and Sakellaridis, Baiying Liu and I have proven a summation formula analogous to the Poisson summation formula for the subscheme cut out of three quadratic spaces $(V_i,Q_i)$ of even dimension by the equation
 
$Q_1(v_1)=Q_2(v_2)=Q_3(v_3)$.
 

Circuit Lower Bounds for Nondeterministic Quasi-Polytime: An Easy Witness Lemma for NP and NQP

Cody Murray
Massachusetts Institute of Technology
March 26, 2018

We prove that if every problem in NP has n^k-size circuits for a fixed constant k, then for every NP-verifier and every yes-instance x of length n for that verifier, the verifier's search space has a witness for x that can be encoded with a circuit of only n^O(k^3) size. An analogous statement is proved for nondeterministic quasi-polynomial time, i.e., NQP = NTIME[n^(log n)^O(1)]. This significantly extends the Easy Witness Lemma of Impagliazzo, Kabanets, and Wigderson [JCSS'02] which only held for larger nondeterministic classes such as NEXP.