Coherence and lattices

Matthew Stover
Temple University
March 27, 2019

Abstract: I will survey (in)coherence of lattices in semisimple Lie groups, with a view toward open problems and connections with the geometry of locally symmetric spaces. Particular focus will be placed on rank one lattices, where I will discuss connections with reflection groups,  "algebraic" fibrations of lattices, and analogies with classical low-dimensional topology.

 

Factors of sparse polynomials: structural results and some algorithms

Shubhangi Saraf
Member, School of Mathematics
March 26, 2019
Are factors of sparse polynomials sparse? This is a really basic question and we are still quite far from understanding it in general.

    In this talk, I will discuss a recent result showing that this is in some sense true for multivariate polynomials when the polynomial has each variable appearing only with bounded degree. Our sparsity bound uses techniques from convex geometry, such as the theory of Newton polytopes and an approximate version of the classical Caratheodory's Theorem.

    One-relator groups, non-positive immersions and coherence

    Henry Wilton
    Cambridge University
    March 26, 2019

    Abstract: There seems to be an analogy between the classes of fundamental groups of compact 3-manifolds and of one-relator groups.  (Indeed, many 3-manifold groups are also one-relator groups.) For instance, Dehn’s Lemma for 3-manifolds (proved by Papakyriakopoulos) can be seen as analogous to Magnus’ Freiheitssatz for one-relator groups.  But the analogy is still very incomplete, and since there are deep results on each side that have no analogue on the other, there is a strong incentive to flesh it out.

    On the Approximation Resistance of Balanced Linear Threshold Functions

    Aaron Potechin
    University of Chicago
    March 25, 2019
    Constraint satisfaction problems (CSPs) are a central topic of study in computer science. A fundamental question about CSPs is as follows. Given a CSP where each constraint has the form of some predicate P and almost all of the constraints can be satisfied, is there a randomized polynomial time algorithm which is guaranteed to do significantly better in expectation than a random assignment? If so, then we say that the predicate P is approximable. If not, then we say that P is approximation resistant.