Graduate Colloquium

The graduate students of the Mathematics Department coordinate a quarterly colloquium. The talks are generally every Thursday from 4-5 PM, with an informal tea (get-together) beforehand.


Winter 2021 Grad Colloquium Thursdays
talk @ 4pm, "tea" @ ~3:30pm, California Time
Meeting ID: 946 8725 0529 -- Passcode: 674336 -- Direct link
For further information please contact
Deewang Bhamidipati (
or David Rubinstein (

Schedule (click dates for title and abstract)

1/21 Andrew Kobin UCSC
2/11 Ryan Pugh
2/18 Cheyenne Dowd UCSC
2/25 Sam Miller UCSC
3/4 Ezekiel Lemann SUNY Binghamton

Thursday, January 21, 2021

Andrew Kobin, UC Santa Cruz

What is a stack?

Many classification problems in math are made harder by nontrivial automorphisms of the objects one is trying to classify. Groupoids, and ultimately stacks, are the right language to solve these problems in a satisfying way. In this talk, I will gently ease the audience into the waters of algebraic geometry while sprinkling in the motivating principles behind stacks. Then we will look at some important examples of algebraic stacks, including quotient stacks and the moduli stack of elliptic curves.

Thursday, February 11, 2021

Ryan Pugh, UC Santa Cruz

An Introduction to Stability and Banach Algebras

We'll first introduce ourselves to Toeplitz and Hankel matrices and explore a few of their properties. We'll then turn our attention towards the ideas of approximation methods and stability of sequences of operators. As if that weren't enough exciting content, we'll end the talk with a discussion on Banach algebras, a bit of Gelfand theory and C*-Algebras, all venerable additions to our mathematical toolboxes. One goal of this talk is to show how the things we learn in functional analysis can pop up in different contexts, so I'll do my best to point these out along our journey.

Thursday, February 18, 2021

Cheyenne Dowd, UC Santa Cruz

An Introductory Look at Chaos in the Sitnikov Problem

The Sitnikov problem is a well-known problem in n-body dynamics; it explores the behavior of this 3-body problem with a remarkable set of solutions. We will discuss the well-known Kepler problem of two bodies, and then introduce the third body per the Sitnikov problem. We will then discuss both solutions to this system, and examine the chaotic behavior which it exhibits.

Thursday, February 25, 2021

Sam Miller, UC Santa Cruz

Checkers, stacks and other fun things: a potpourri of combinatorial puzzles and games

Combinatorial game theory is the study of sequential games with perfect information. We survey an assortment of combinatorial puzzles and games, including the Knight's Tour and Conway's Checkers, and present the audience with satisfying combinatorial proofs. Included in this presentation will be original results proven by the presenter prior to entering UC Santa Cruz. No background in combinatorics is required.

Thursday, March 4, 2021

Ezekiel Lemann, SUNY Binghamton

Introduction to the Waldhausen S-Construction

We will give an overview of the construction of K-theory due to Friedhelm Waldhausen and mention a few uses of K-groups.