Colloquia - Fall 2024

If you are interested in giving a talk, please email Dr. Guillermo Alesandroni (galesandroni@csuchico.edu).

Colloquia are typically held on Friday in Holt 175. Please see below for specific information. Refreshments are served at 3:45 pm and the talk begins at 4:00 pm. Everyone is invited to attend!

Upcoming talk

Friday, December 13 — Holt 175, 4:00pm 

Russell J. Bowater — Independent statistical consultant

Title: The 7 hardest lessons to learn in statistics

Abstract: What is the current state of the theory of statistical inference? Is it essentially in a good state except for a relatively small number of issues that need to be tidied up? Or is what is usually presented as being the standard and accepted theory of statistical inference so full of conceptual holes that it is nothing short of an embarrassment for anyone who wishes to describe themselves as a statistician? This talk explores these questions by presenting lessons that arguably need to be learnt but have proved difficult to learn for reasons that to a great extent are not related to doing good independent and impartial science. By exposing ourselves to such an uncomfortable level of introspection, a greater understanding can be gained about what we have done, where we are at and where we should be going.

Past talks

Friday, November 22 — Holt 175, 4:00pm

Rick Danner — University of Vermont

Title: Convex Geometry of Building Sets

Abstract: Building sets were introduced in the study of wonderful compactifications of hyperplane arrangement complements and were later generalized to finite meet-semilattices. Convex geometries, the duals of antimatroids, offer a robust combinatorial abstraction of convexity. Supersolvable convex geometries and antimatroids appear in the study of poset closure operators, Coxeter groups, and matroid activities. We prove that the building sets on a finite meet-semilattice form a supersolvable convex geometry.  As an application, we demonstrate that building sets and nested set complexes respect certain restrictions of finite meet-semilattices unifying and extending results of several authors. This is joint work with Spencer Backman.

Friday, November 15 — Holt 175, 4:00pm

James Upton — UC Santa Cruz

Title: The Goss Zeta Function

Abstract: A central theme in number theory is the analogy between rational numbers and rational functions over a field F. When F is finite, Goss constructed a zeta function which, under this analogy, plays the analogue of the Riemann zeta function. This talk describes the history of the Goss zeta function and its many interesting parallels to the Riemann zeta function. We describe some classical results concerning its special values, as well as what is known about the distribution of its zeros. We also describe some recent work generalizing these results to arbitrary function fields over F. This is joint work with Joe Kramer-Miller.

Friday, November 1 — Holt 175, 4:00pm

Jon Aycock — UC San Diego

Title: Jacobians of Graphs via Edges and Iwasawa Theory

Abstract: The Jacobian (or sandpile group) is an algebraic invariant of a graph that plays a similar role to the class group in classical number theory. There are multiple recent results controlling the sizes of these groups in Galois towers of graphs that mimic the classical results in Iwasawa theory, though the connection to the values of the Ihara zeta function often requires some adjustment. In this talk we will give a new way to view the Jacobian of a graph that more directly centers the edges of the graph, construct a module over the relevant Iwasawa algebra that nearly corresponds to the interpolated zeta function, and discuss where the discrepancy comes from.

Friday, October 25 — Holt 175, 4:00pm

Michael Coons — CSU Chico

Title: Some results on aperiodic order from our NSF Research Experience for Undergraduates.

Abstract: In Spring 2024 I gave a talk called “A question on aperiodic order for NSF Research Experiences for Undergraduates,” which outlined my ideas for the upcoming summer NSF REUT program held here at CSU Chico. I started that talk by defining the Stern sequences and Takagi function, then showed two pictures that looked strangely similar with the idea of understanding this similarity. This is indeed how we started our summer program.  This talk will effectively be a ‘part 2’ of my previous talk. Here, I will report on the work accomplished by my group as part of this past summer’s NSF REUT. The areas we will touch on will be connected to several different disciplines including mathematics (of course), theoretical computer science, and mathematical physics.  I would particularly like to invite students that are thinking about having a research experience in mathematics here at CSU Chico to see one option of what is possible!

Friday, October 18 — Holt 175, 4:00pm

Lea Kenigsberg — UC Davis

Title: The string topology coproduct: what is it, and why it is so cool.

Abstract: Let M be a smooth manifold, for example a higher dimensional sphere.  The free loop space is the space of all maps from the circle to M. The loop space admits a very rich structure which reveals deep geometric and topological information about manifolds.  In this talk I will describe the string topology coproduct, and the kind of information it encodes. In particular, I will discuss interesting connections to invariants from algebraic K-theory and fixed point theory. This is based on joint work with Noah Porcelli.

Friday, October 4 — Holt 175, 3:00pm (*special time)

Rusiru Gambheera — UC Santa Barbara

Title: Iwasawa Theory for branched Z_p-towers of finite graphs

Abstract:  Motivated by the analogy between number theory and graph theory, one can study how the number of spanning trees varies in infinite Galois towers above a fixed finite connected graph just as one does for the class number in classical Iwasawa theory for number fields. This has been done using both analytic and algebraic methods for the case where the intermediate morphims of graphs are unramified. We generalize this to the ramified towers of graphs using algebraic methods. This is joint work with Daniel Vallieres.

Friday, September 13 — Holt 175, 4:00pm

Daniel Vallieres — CSU Chico

Title: Have you ever wondered if graphs should have legs?

Abstract:  Graph theorists have been considering graphs with legs for quite some time now for various different reasons.  In this talk, we will explain why this enlargement of the category of graphs might be interesting as well from the point of view of the analogy between number theory and graph theory.  

Past Colloquia