Seminars and Colloquia Schedule

Growth of torsion homology in finite coverings and hyperbolic volume

Series
Geometry Topology Seminar
Time
Monday, November 13, 2017 - 13:55 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Thang Le – Georgia Tech –
We discuss the growth of homonoly in finite coverings, and show that the growth of the torsion part of the first homology of finite coverings of 3-manifolds is bounded from above by the hyperbolic volume of the manifold. The proof is based on the theory of L^2 torsion.

Local-to-Global lifting to curves in characterstic p

Series
Algebra Seminar
Time
Monday, November 13, 2017 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Renee Bell – Massachusetts Institute of Technology –
Given a Galois cover of curves X to Y with Galois group G which is totally ramified at a point x and unramified elsewhere, restriction to the punctured formal neighborhood of x induces a Galois extension of Laurent series rings k((u))/k((t)). If we fix a base curve Y , we can ask when a Galois extension of Laurent series rings comes from a global cover of Y in this way. Harbater proved that over a separably closed field, this local-to-global principle holds for any base curve if G is a p-group, and gave a condition for the uniqueness of such an extension. Using a generalization of Artin-Schreier theory to non-abelian p-groups, we characterize the curves Y for which this lifting property holds and when it is unique, but over a more general ground field.

Diophantine Equations and p-adic Integration

Series
Research Horizons Seminar
Time
Wednesday, November 15, 2017 - 12:10 for 1 hour (actually 50 minutes)
Location
skiles 006
Speaker
Joseph Rabinoff – GT Math
A motivating problem in number theory and algebraic geometry is to find all integer-valued solutions of a polynomial equation. For example, Fermat's Last Theorem asks for all integer solutions to x^n + y^n = z^n, for n >= 3. This kind of problem is easy to state, but notoriously difficult to solve. I'll explain a p-adic method for attacking Diophantine equations, namely, p-adic integration and the Chabauty--Coleman method. Then I'll talk about some recent joint work on the topic.

Taut foliations and Sutured Floer Homology

Series
Geometry Topology Student Seminar
Time
Wednesday, November 15, 2017 - 13:55 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Surena Hozoori – Georgia Tech
It is known that a class of codimension one foliations, namely "taut foliations", have subtle relation with the topology of a 3-manifold. In early 80s, David Gabai introduced the theory of "sutured manifolds" to study these objects and more than 20 years later, Andres Juhasz developed a Floer type theory, namely "Sutured Floer Homology", that turned out to be very useful in answering the question of when a 3-manifold with boundary supports a taut foliation.

t-Haar multipliers revisited

Series
Analysis Seminar
Time
Wednesday, November 15, 2017 - 13:55 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Cristina Pereyra – University of New Mexico
t-Haar multipliers are examples of Haar multipliers were the symbol depends both on the frequency variable (dyadic intervals) and on the space variable, akin to pseudo differential operators. They were introduced more than 20 years ago, the corresponding multiplier when $t=1$ appeared first in connection to the resolvent of the dyadic paraproduct, the cases $t=\pm 1/2$ is intimately connected to direct and reverse inequalities for the dyadic square function in $L^2$, the case $t=1/p$ naturally appears in the study of weighted inequalities in $L^p$. Much has happened in the theory of weighted inequalities in the last two decades, highlights are the resolution of the $A_2$ conjecture (now theorem) by Hyt\"onen in 2012 and the resolution of the two weight problem for the Hilbert transform by Lacey, Sawyer, Shen and Uriarte Tuero in 2014. Among the competing methods used to prove these results were Bellman functions, corona decompositions, and domination by sparse operators. The later method has gained a lot of traction and is being widely used in contexts beyond what it was originally conceived for in work of Lerner, several of these new applications have originated here at Gatech. In this talk I would like to tell you what I know about t-Haar multipliers (some work goes back to my PhD thesis and joint work with Nets Katz and with my former students Daewon Chung, Jean Moraes, and Oleksandra Beznosova), and what we ought to know in terms of sparse domination.

Planar Graph Perfect Matching is in NC

Series
Joint ACO and ARC Seminar
Time
Thursday, November 16, 2017 - 13:30 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Vijay Vazirani – UC Irvine
Is matching in NC, i.e., is there a deterministic fast parallel algorithm for it? This has been an outstanding open question in TCS for over three decades, ever since the discovery of Random NC matching algorithms. Within this question, the case of planar graphs has remained an enigma: On the one hand, counting the number of perfect matchings is far harder than finding one (the former is #P-complete and the latter is in P), and on the other, for planar graphs, counting has long been known to be in NC whereas finding one has resisted a solution!The case of bipartite planar graphs was solved by Miller and Naor in 1989 via a flow-based algorithm. In 2000, Mahajan and Varadarajan gave an elegant way of using counting matchings to finding one, hence giving a different NC algorithm.However, non-bipartite planar graphs still didn't yield: the stumbling block being odd tight cuts. Interestingly enough, these are also a key to the solution: a balanced odd tight cut leads to a straight-forward divide and conquer NC algorithm. The remaining task is to find such a cut in NC. This requires several algorithmic ideas, such as finding a point in the interior of the minimum weight face of the perfect matching polytope and uncrossing odd tight cuts.Joint work with Nima Anari.

Isoperimetric inequalities for convex cones

Series
Math Physics Seminar
Time
Thursday, November 16, 2017 - 13:30 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Lotfi Hermi – Florida International University –

This is part of the 2017 Quolloquium series.

We use the weighted isoperimetric inequality of J. Ratzkin for a wedge domain in higher dimensions to prove new isoperimetric inequalities for weighted $L_p$-norms of the fundamental eigenfunction of a bounded domain in a convex cone-generalizing earlier work of Chiti, Kohler-Jobin, and Payne-Rayner. We also introduce relative torsional rigidity for such domains and prove a new Saint-Venant-type isoperimetric inequality for convex cones. Finally, we prove new inequalities relating the fundamental eigenvalue to the relative torsional rigidity of such a wedge domain thereby generalizing our earlier work to this higher dimensional setting, and show how to obtain such inequalities using the Payne interpretation in Weinstein fractional space. (Joint work with A. Hasnaoui)

Kushnirenko's Theorem

Series
Student Algebraic Geometry Seminar
Time
Friday, November 17, 2017 - 10:00 for 1 hour (actually 50 minutes)
Location
Skiles 114
Speaker
Timothy Duff – GA Tech
Motivated by the general problem of polynomial system solving, we state and sketch a proof Kushnirenko's theorem. This is the simplest in a series of results which relate the number of solutions of a "generic" square polynomial system to an invariant of some associated convex bodies. For systems with certain structure (here, sparse coefficients), these refinements may provide less pessimistic estimates than the exponential bounds given by Bezout's theorem.

Semiclassical Spectral Estimates with Renainder Terms

Series
Math Physics Seminar
Time
Friday, November 17, 2017 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Timo Weidl – Univ. Stuttgart –

This is part of the 2017 Quolloquium series.

Starting from the classical Berezin- and Li-Yau-bounds onthe eigenvalues of the Laplace operator with Dirichlet boundaryconditions I give a survey on various improvements of theseinequalities by remainder terms. Beside the Melas inequalitywe deal with modifications thereof for operators with and withoutmagnetic field and give bounds with (almost) classical remainders.Finally we extend these results to the Heisenberg sub-Laplacianand the Stark operator in domains.

Disproof of a packing conjecture of Alon and Spencer

Series
Combinatorics Seminar
Time
Friday, November 17, 2017 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Huseyin Acan – Rutgers University
A 1992 conjecture of Alon and Spencer says, roughly, that the ordinary random graph G_{n,1/2} typically admits a covering of a constant fraction of its edges by edge-disjoint, nearly maximum cliques. We show that this is not the case. The disproof is based on some (partial) understanding of a more basic question: for k ≪ \sqrt{n} and A_1, ..., A_t chosen uniformly and independently from the k-subsets of {1…n}, what can one say about P(|A_i ∩ A_j|≤1 ∀ i≠j)? Our main concern is trying to understand how closely the answers to this and a related question about matchings follow heuristics gotten by pretending that certain (dependent) choices are made independently. Joint work with Jeff Kahn.

From Kepler to Kolmogorov: the problem of stability

Series
Dynamical Systems Working Seminar
Time
Friday, November 17, 2017 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 154
Speaker
Bhanu Kumar – GT Math
This lecture will discuss the stability of perturbations of integrable Hamiltonian systems. A brief discussion of history, integrability, and the Poincaré nonintegrability theorem will be followed by the proof of the theorem of Kolmogorov on persistence of invariant tori. Time permitting, the problem of small divisors may be briefly discussed. This lecture wIll follow the slides from the Satellite Dynamics and Space Missions 2017 summer school held earlier this semester in Viterbo, Italy.

Sage

Series
AMS Club Seminar
Time
Friday, November 17, 2017 - 16:00 for 1 hour (actually 50 minutes)
Location
Skiles 001
Speaker
Maxie Schmidt – Georgia Tech –
Sage is widely considered to be the defacto open-source alternative to Mathematica that is freely available for download to users on most standard platforms at sagemath.org. New users to Sage are also able to use its capabilities from any webbrowser and other useful Linux-only software by registering for a free account on the Sage Math Cloud platform (SMC). In addition to providing users with excellent documentation, Sage allows its users to develop spohisticated mathematics applications using Python and other excellent open-source developer tools that are well tested under both Unix / Linux and Windows environments. In this two-week workshop we provide a user-friendly introduction to Sage for beginners starting from first principles in Python, though some coding experience in other languages will of course be helpful to participants. The main project we will be focusing on over the course of the workshop is an extension of the open-source library provided by the Tilings Gap Distributions and Pair Correlation Project developed by the workshop guide at the University of Washington this and last year. This application will allow participants in the workshop to hone their coding skills in Sage by working on an extension of a real-world computational mathematics application in statistics and geometry. Prospective participants can gain a heads-up on the workshop by visiting the syllabus webpage freely available for modification online at https://github.com/maxieds/WXMLTilingsHOWTO/wiki. The workshop guide will also offer continued free technical support on Sage, Python programming, and Linux to participants in the workshop after the two-week session is complete. Future AMS workshop sessions focusing on other Sage programming topics may be run later based on feedback from this proto-session. Faculty and postdocs are welcome to attend. See you all there on Friday!