Algebra & Number Theory Seminar


Winter 2021 ANT Zoominar
Fridays @ 3pm California Time 
Meeting ID: 9045829721 --- password: seminar
For further information please contact
Professor Beren Sanders

Schedule (click dates for title and abstract) 

2/19 Libby Taylor Stanford University
2/26 Leo Herr University of Utah
3/12 Hatice Mutlu Akaturk UCSC

Friday, February 19, 2021

Libby Taylor, Stanford University

Derived equivalences of gerbey curves

We study derived equivalences of certain stacks over genus 1 curves, which arise as connected components of the Picard stack of a genus 1 curve. To this end, we develop a theory of integral transforms for these algebraic stacks. We use this theory to answer the question of when two stacky genus 1 curves are derived equivalent. We use integral transforms and intersection theory on stacks to answer the following questions: if C'=Pic^d (C), is C=Pic^f (C') for some integer f? If C'=Pic^d (C) and C''=Pic^f (C'), then is C''=Pic^g (C) for some integer g?

Friday, February 26, 2021

Leo Herr, University of Utah

Log intersection theory and the product formula
(joint with Jonathan Wise, Y.P. Lee, and You-Cheng Chou)

Log structures stratify a space and manage mild singularities. Cohomological invariants are defined via an inverse limit of blowups akin to a rigid analytic or Berkovich space. When schemes are enriched with log structure, intersections and other fiber products are different from the intersections of underlying schemes. I define a "log intersection product," or log Gysin map that takes place on the log intersection and mimics Fulton's intersection theory. This can be defined in log versions of Chow or K theory groups, similar to Shokurov's bChow groups in birational geometry. As an application, I prove a log version of the product formula in Gromov-Witten theory.

Friday, March 12, 2021

Hatice Mutlu Akaturk, UCSC

Monomial posets and their Lefschetz invariants
(joint with Serge Bouc and Robert Boltje)

The Euler-Poincaré characteristic of a given poset X is defined as the alternating sum of the orders of the sets of chains Sdn(X) with cardinality n + 1 over the natural numbers n. Given a finite group G, Thévenaz extended this definition to G-posets and defined the Lefschetz invariant of a G-poset X as the alternating sum of the G-sets of chains Sdn(X) with cardinality n+1 over the natural numbers n which is an element of Burnside ring B(G). Let A be an abelian group. We will introduce the notions of A-monomial G-posets and A-monomial G-sets, and state some of their categorical properties. The category of A-monomial G-sets gives a new description of the A-monomial Burnside ring BA(G). We will also introduce Lefschetz invariants of A-monomial G-posets, which are elements of BA(G). An application of the Lefschetz invariants of A-monomial G-posets is the A-monomial tensor induction. Another application is a work in progress that aims to give a reformulation of the canonical induction formula for ordinary characters via A-monomial G-posets and their Lefschetz invariants. For this reformulation we will introduce A-monomial G-simplicial complexes and utilize the smooth G-manifolds and complex G-equivariant line bundles on them.