Seminars and Colloquia by Series

Monday, April 22, 2019 - 12:50 , Location: Skiles 005 , Joe Kileel , Princeton University , , Organizer: Justin Chen
Monday, April 15, 2019 - 12:50 , Location: Skiles 005 , Kalina Mincheva , Yale University , , Organizer: Yoav Len
Monday, April 8, 2019 - 12:50 , Location: Skiles 005 , Mengyuan Zhang , University of California, Berkeley , , Organizer: Justin Chen
Monday, April 1, 2019 - 12:50 , Location: Skiles 005 , TBA by Maria Angelica Cueto , Ohio State University , , Organizer: Yoav Len
Saturday, March 30, 2019 - 14:00 , Location: Atlanta , Georgia Tech Tropical Arithmetic and Combinatorial Algebraic-geometry , Georgia Institute of Technology , Organizer: Yoav Len

This is a two day conference (March 30-31) to be held at Georgia Tech on algebraic geometry and related areas. We will have talks by Sam Payne, Eric Larson, Angelica Cueto, Rohini Ramadas, and Jennifer Balakrishnan. See for more information.

Monday, March 25, 2019 - 12:50 , Location: Skiles 005 , Ben Blum-Smith , NYU , Organizer: Josephine Yu

If a finite group $G$ acts on a Cohen-Macaulay ring $A$, and the order of $G$ is a unit in $A$, then the invariant ring $A^G$ is Cohen-Macaulay as well, by the Hochster-Eagon theorem. On the other hand, if the order of $G$ is not a unit in $A$ then the Cohen-Macaulayness of $A^G$ is a delicate question that has attracted research attention over the last several decades, with answers in several special cases but little general theory. In this talk we show that the statement that $A^G$ is Cohen-Macaulay is equivalent to a statement quantified over the inertia groups for the action of G$ on $A$ acting on strict henselizations of appropriate localizations of $A$. In a case of long-standing interest—a permutation group acting on a polynomial ring--we show how this can be applied to find an obstruction to Cohen-Macaulayness that allows us to completely characterize the permutation groups whose invariant ring is Cohen-Macaulay regardless of the ground field. This is joint work with Sophie Marques.

Friday, March 15, 2019 - 14:00 , Location: Skiles 005 , Frank Sottile , Texas A&M , Organizer: Kirsten Wickelgren
Problems from enumerative geometry have Galois groups. Like those from field extensions, these Galois groups reflect the internal structure of the original problem.  The Schubert calculus is a class of problems in enumerative geometry that is very well understood, and may be used as a laboratory to study new phenomena in enumerative geometry.I will discuss this background, and sketch a picture that is emerging from a sustained study of Schubert problems from the perspective of Galois theory.  This includes a conjecture concerning the possible Schubert Galois groups, a partial solution of the inverse Galois problem, as well as glimpses of the outline of a possible classification of Schubert problems for their Galois groups.
Monday, March 11, 2019 - 12:50 , Location: Skiles 005 , Borys Kadets , MIT , , Organizer: Yoav Len

Let X be a degree d curve in the projective space P^r.

A general hyperplane H intersects X at d distinct points; varying H defines a monodromy action on X∩H. The resulting permutation group G is the sectional monodromy group of X. When the ground field has characteristic zero the group G is known to be the full symmetric group.

By work of Harris, if G contains the alternating group, then X satisfies a strengthened Castelnuovo's inequality (relating the degree and the genus of X).

The talk is concerned with sectional monodromy groups in positive characteristic. I will describe all non-strange non-degenerate curves in projective spaces of dimension r>2 for which G is not symmetric or alternating. For a particular family of plane curves, I will compute the sectional monodromy groups and thus answer an old question on Galois groups of generic trinomials.

Monday, March 4, 2019 - 12:50 , Location: Skiles 005 , Chris Eur , University of California, Berkeley , , Organizer: Justin Chen

We introduce a certain nef generating set for the Chow ring of the wonderful compactification of a hyperplane arrangement complement. This presentation yields a monomial basis of the Chow ring that admits a geometric and combinatorial interpretation with several applications. Geometrically, one can recover Poincare duality, compute the volume polynomial, and identify a portion of a polyhedral boundary of the nef cone. Combinatorially, one can generalize Postnikov's result on volumes of generalized permutohedra, prove Mason's conjecture on the log-concavity of independent sets for certain matroids, and define a new valuative invariant of a matroid that measures its closeness to uniform matroids. This is an on-going joint work with Connor Simpson and Spencer Backman.

Monday, February 18, 2019 - 13:00 , Location: Skiles 005 , Robert Walker , U Michigan , Organizer: Josephine Yu
We survey dissertation work of my academic sister Sarah Mayes-Tang (2013 Ph.D.). As time allows, we aim towards two objectives. First, in terms of combinatorial algebraic geometry we weave a narrative from linear star configurations in projective spaces to matroid configurations therein, the latter being a recent development investigated by the quartet of Geramita -- Harbourne -- Migliore -- Nagel. Second, we pitch a prospectus for further work in follow-up to both Sarah's work and the matroid configuration investigation.