# Events - 2019

Wednesday, November 13, 2019 — 3:30 PM EST

## Analysis Seminar

Boyu Li, University of Victoria

"Amenable and Non-amenable Semigroups"

Since Nica introduced the notion of amenability of quasi-lattice ordered semigroups, the amenability for many classes of semigroups remain unanswered. We will give a brief overview of semigroup amenability, and show some recent developments on this topic using dilation theory. In particular, we shall show that Artin monoids are non-amenable except the class of right-angled. This is a joint work with Marcelo Laca.

MC 5417

Tuesday, November 12, 2019 — 3:00 PM EST

## Special Colloquium

Daniel Le, University of Toronto

"Congruences between modular forms"

Tuesday, November 12, 2019 — 2:00 PM EST

## Computability Learning Seminar

Dino Rossegger, Department of Pure Mathematics, University of Waterloo

"Determinacy in second order arithmetic"

Tuesday, November 12, 2019 — 1:30 PM EST

## Number Theory Seminar

Arpita Kar, Queen's University

"Some reflections on the Riemann Hypothesis"

Thursday, November 7, 2019 — 11:00 AM EST

## Model Theory Learning Seminar

Wilson Poulter, Department of Pure Mathematics, University of Waterloo

"NIP VI"

We finish section 2.2.2 of Simon's Guide to NIP theories and move on to 2.2.3.

MC 5413

Wednesday, November 6, 2019 — 3:30 PM EST

## Analysis Seminar

Alexandru Nica, Department of Pure Mathematics, University of Waterloo

"Free probabilistic aspects of meandric systems"

Tuesday, November 5, 2019 — 2:30 PM EST

## Valuative Tree Seminar

Andrej Vukovic, Department of Pure Mathematics, University of Waterloo

We continue where last week's discussion left off by discussing the classification of semivaluations in the valuative tree. Then we return to our study of plane polynomial dynamics.

M3 3103

Tuesday, November 5, 2019 — 2:00 PM EST

## Computability Learning Seminar

Luke MacLean, Department of Pure Mathematics, University of Waterloo

"Reverse Mathematics"

We say that $S \subseteq \mathcal{P}(\omega)$ is an $\omega$-model of a subsystem of second order arithmetic if the $L_2$ structure $(\omega, S, +, \cdot, 0, 1, <)$ correctly models the subsystem in question. The goal of this lecture will be to prove that there is an $\omega$-model of $WKL_0$ consisting entirely of low sets.

This will involve learning about PA degrees and the low basis theorem.

All are welcome.

MC 5413

Wednesday, October 30, 2019 — 3:30 PM EDT

## Joint PM/CO Grad Colloquium

Hayley Reid, Department of Pure Mathematics, University of Waterloo

"Cutting a square into triangles of equal area"

Tuesday, October 29, 2019 — 2:30 PM EDT

## Valuative Tree Seminar

Andrej Vukovic, Department of Pure Mathematics, University of Waterloo

We review aspects of the theory of Berkovich spaces, including quasimonomial valuations and invariants associated to a valuation. We then discuss birational geometry, introducing blowups and log resolutions of ideals. We discuss dual graphs and describe the classification of semivaluations in the valuative tree. We conclude by returning to our earlier study of plane polynomial dynamics.

M3 3103

Tuesday, October 29, 2019 — 2:00 PM EDT

## Computability Learning Seminar

Luke MacLean, Department of Pure Mathematics, University of Waterloo

"Reverse Mathematics (part 2)"

Having heard a brief overview of the basics of reverse mathematics, we will continue to learn about the system RCA_0 and the theorems provable therein.

Attendance of part 1 is not required, only an interest in logic and computability.

MC 5413

Monday, October 28, 2019 — 4:00 PM EDT

## Colloquium

Alexander Yong, University of Illinois at Urbana-Champaign

"Complexity, combinatorial positivity, and Newton polytopes"

The Nonvanishing Problem asks if a coefficient of a polynomial is nonzero. Many families of polynomials in algebraic combinatorics admit combinatorial counting rules and simultaneously enjoy having saturated Newton polytopes (SNP). Thereby, in amenable cases, Nonvanishing is in the complexity class of problems with “good characterizations”. This suggests a new algebraic combinatorics viewpoint on complexity theory.

Thursday, October 24, 2019 — 4:00 PM EDT

Dan Ursu, Department of Pure Mathematics, University of Waterloo

"Ruler-compass constructions"

Wednesday, October 23, 2019 — 3:30 PM EDT

## Analysis Seminar

Don Hadwin, University of New Hampshire

"Tracial Stability for C*-algebras (and Groups)"

Tuesday, October 22, 2019 — 2:00 PM EDT

## Computability Learning Seminar

Luke MacLean, Department of Pure Mathematics, University of Waterloo

"REVERSE MATHEMATICS"

While most of mathematics is concerned with using a set of axioms to prove theorems, reverse mathematics is a relatively new form of mathematical logic that seeks to determine which axioms are required to prove certain theorems. This gives a notion of the “strength” of a certain theorem by looking at which theorems imply it, and which are implied by it.

Tuesday, October 22, 2019 — 2:00 PM EDT

## PhD Thesis Defence

Zack Cramer, Department of Pure Mathematics, University of Waterloo

"Compressible Matrix Algebras and the Distance from Projections to Nilpotents"

Tuesday, October 22, 2019 — 1:30 PM EDT

## Number Theory Seminar

Adian Diaconu, University of Minnesota

"Moments of L-functions"

I will begin by discussing some recent results (joint in part with Ian Whitehead) about moments of quadratic Dirichlet L-functions. While our understanding of these moments over number fields still remains largely elusive, their function field analogs are more tractable. The main focus will be to describe some partial results in the function field setting. (Joint work with Jonas Bergström, Dan Petersen and Craig Westerland.)

MC 5417

Friday, October 11, 2019 — 1:30 PM EDT

## Geometry & Topology Seminar

Gabriel Islambouli, Deaprtment of Pure Mathematics, University of Waterloo

"Smooth 4-manifolds and the Pants Complex"

Thursday, October 10, 2019 — 11:00 AM EDT

## Model Theory Learning Seminar

Marco Handa, Department of Pure Mathematics, University of Waterloo

"NIP IV"

We begin section 2.2.1 of Simon's Guide to NIP theories.

MC 5413

Wednesday, October 9, 2019 — 3:30 PM EDT

## Analysis Seminar

Kevin Hare, Department of Pure Mathematics, University of Waterloo

"Entropy of Self-similar Measures"

It is known that a self-similar measure is either purely singular or absolutely continuous.  Despite this, for most measures we cannot say which case we are in.  One technique that has proved promising is the study of the Garsia Entropy of the measure.  In this talk I will discuss the history, properties and recent results for self-similar measures and Garsia Entropy.

MC 5417

Tuesday, October 8, 2019 — 2:30 PM EDT

## Valuative Tree Seminar

Brett Nasserden, Department of Pure Mathematics, University of Waterloo

"Normal forms of dominant polynomial morphisms of the affine plane"

Tuesday, October 8, 2019 — 1:30 PM EDT

## Number Theory Seminar

Ertan Elma, Department of Pure Mathematics, University of Waterloo

"Discrete Mean Values of Dirichlet L-functions"

Let χ be a Dirichlet character modulo a prime number p ⩾ 3 and let \mathfrak a_χ:=(1-χ(-1))/2. Define the mean value
\begin{align*}
\mathcal{M}_{p}(s,\chi):=\frac{2}{p-1}\sum_{\substack{\psi \bmod p\\\psi(-1)=-1}}L(1,\psi)L(s,\chi\overline{\psi})
\end{align*}
for a complex number s such that s≠ 1 if \mathfrak a _χ=1.

Monday, October 7, 2019 — 4:00 PM EDT

## Colloquium

Jeffrey Diller, University of Notre Dame

"A transcendental first dynamical degree"

Friday, October 4, 2019 — 2:30 PM EDT

## Geometry & Topology Seminar

Fenglong You, University of Alberta

"Structures of relative Gromov-Witten theory"

Thursday, October 3, 2019 — 11:00 AM EDT

## Model Theory Learning Seminar

Steven Lazzaro, McMaster University

"NIP III"

We begin section 2.2 of Simon's Guide to NIP theories.

MC 5413

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