# Events - March 2019

Friday, March 29, 2019 — 2:30 PM EDT

## Geometry & Topology Seminar

Martin Pinsonnault, Western University

"Stability of Symplectomorphism Groups of Small Rational Surfaces"

Thursday, March 28, 2019 — 4:00 PM EDT

## Special Colloquium

Tobias Fritz, Perimeter Institute for Theoretical Physics

"Real algebra, random walks, and information theory"

Wednesday, March 27, 2019 — 3:30 PM EDT

## Analysis Seminar

Andre Kornell, UC Davis

"Quantum Extensions of Ordinary Maps"

Wednesday, March 27, 2019 — 3:30 PM EDT

## Computability Learning Seminar

Michael Deveau, Department of Pure Mathematics, University of Waterloo

"Generalizing $\omega^k$-c.e. for Relativization - Part 2"

We finish the proof of a characterization of $A \leq_{bT} B^b$ that we started last time. We then use this to motivate a more general characterization, namely when $A \leq{bT} B^{nb}$. Finally, we begin the proof of a weak non-collapse theorem which uses this expanded characterization.

MC 5413

Tuesday, March 26, 2019 — 5:00 PM EDT

## Pure Math Grad Colloquium

Ragini Singhal, Department of Pure Mathematics, University of Waterloo

"Surfaces, Minimal surfaces, Willmore surfaces and much more"

Tuesday, March 26, 2019 — 2:30 PM EDT

## Algebra Seminar

Ben Webster, Department of Pure Mathematics, University of Waterloo

"Coulomb, Galois, Gelfand-Tsetlin"

In the grand tradition of naming objects after mathematicians who knew nothing about them, I'll talk a bit about Galois orders, their Gelfand-Tsetlin modules, and how most important examples are Coulomb branches.

Tuesday, March 26, 2019 — 12:30 PM EDT

## Number Theory Seminar

Vandita Patel, University of Toronto

"A Galois property of even degree Bernoulli polynomials"

Let $k$ be an even integer such that $k$ is at least $2$. We give a (natural) density result to show that for almost all $d$ at least $2$, the equation $(x+1)^k + (x+2)^k + ... + (x+d)^k = y^n$ with $n$ at least $2$, has no integer solutions $(x,y,n)$. The proof relies upon some Galois theory and group theory, whereby we deduce some interesting properties of the Bernoulli polynomials. This is joint work with Samir Siksek (University of Warwick).

MC 5417

Tuesday, March 26, 2019 — 10:30 AM EDT

## o-minimal GAGA Seminar

Remi Jaoui, Department of Pure Mathematics, University of Waterloo

"Failure of essential surjectivity"

We consider Example 3.2 of the Bakker-Brunebarbe-Tsimerman paper, of an analytic line bundle on Gm that does not definably trivialise.

MC 5479

Tuesday, March 26, 2019 — 9:00 AM EDT

## Geometry Working Seminar

Patrick Naylor, Department of Pure Mathematics, University of Waterloo

"Trisections of 4-manifolds"

Trisections were introduced by Gay and Kirby in 2013 as a way to study 4-manifolds. They are similar in spirit to a common tool in a lower dimension: Heegaard splittings of 3-manifolds. These both have the advantage of changing problems about manifolds into problems about combinatorics of curves on surfaces. This talk will be a relaxed introduction to these decompositions. Time permitting, we will talk about some recent applications.

MC 5413

Thursday, March 21, 2019 — 4:00 PM EDT

## Model Theory Seminar

Rahim Moosa, Department of Pure Mathematics, University of Waterloo

"Pseudo-finite dimensions IX"

I will discuss the description of approximate subgroups of simple algebraic groups in Udi's "Stable groups and approximate subgroups".

MC 5403

Wednesday, March 20, 2019 — 4:30 PM EDT

## Joint PM/C&O Grad Colloquium

Patrick Naylor, Department of Pure Mathematics, University of Waterloo

“Is any knot not the unknot?”

Ever wanted to learn something about knots? This is your chance! We'll talk about some basics of knot theory, including how to  prove some intuitively obvious' but mathematically tricky results.  Along the way, we'll see knot coloring invariants, polynomial invariants, and more. We'll even show how to produce a knotted surface: a  sphere ($S^2$) in $\mathbb{R}^4$ that is knotted'. This talk will be very accessible and will include many cool pictures.

Wednesday, March 20, 2019 — 3:30 PM EDT

## Analysis Seminar

Yuanhang Zhang, Jilin University

"Connecting invertible analytic Toeplitz operators in $G(\mathcal{T}(\mathcal{P}^{\perp}))$"

We prove that there exists an orthonormal basis $\mathcal{F}$ for classical Hardy space $H^2$, such that each invertible analytic Toeplitz operator $T_\phi$ (i.e. $\phi$ is invertible in $H^\infty$) could be connected to the identity operator via a norm continuous path of invertible elements of the lower triangular operators with respect to $\mathcal{F}$.

Wednesday, March 20, 2019 — 3:30 PM EDT

## Computability Learning Seminar

Michael Deveau, Department of Pure Mathematics, University of Waterloo

"Generalizing $\omega^k$-c.e. for Relativization"

Just as the arithmetic hierarchy characterizes reductions below various Turing jumps of $\emptyset$, Anderson and Csima showed that the Ershov hierarchy -- related to the notion of $\omega^k$-c.e. -- characterizes reductions of bounded Turing jumps of $\emptyset$. We discuss how to relativize this to reductions below bounded Turing jumps of an arbitrary set.

MC 5413

Thursday, March 14, 2019 — 4:30 PM EDT

## Joint Graduate Student Colloquium

Patrick Naylor, Department of Pure Mathematics, University of Waterloo

"Is any knot not the unknot?"

Ever wanted to learn something about knots? This is your chance! We'll talk about some basics of knot theory, including how to prove some intuitively obvious' but mathematically tricky results. Along the way, we'll see knot coloring invariants, polynomial invariants, and more. We'll even show how to produce a knotted surface: a sphere ($S^2$) in $\mathbb{R}^4$ that is knotted'. This talk will be very accessible and will include many cool pictures.

Wednesday, March 13, 2019 — 3:30 PM EDT

## Analysis Seminar

Adam Fuller, Ohio University

"Describing C*-algebras in terms of topological groupoids"

Unital abelian C*-algebras are well understood. They are necessarily isomorphic to C(X), the continuous functions on a compact Hausdorff space X. Studying the topological dynamics on $X$ gives rise to the study of crossed product C*-algebras: a class of relatively well understood of non-abelian operator algebras constructed from a dynamical system.

Tuesday, March 12, 2019 — 12:30 PM EDT

## Number Theory Seminar

Brad Rogers, Queen's University

"Integers in short intervals representable as sums of two squares"

Tuesday, March 12, 2019 — 10:30 AM EDT

## o-minimal GAGA Seminar

Matt Satriano, Department of Pure Mathematics, University of Waterloo

"The Main Theorem"

We jump ahead and begin proving the main algebraization theorem of the Bakker-Brunebarbe-Tsimerman paper – Theorem 3.1.

MC 5479

Tuesday, March 12, 2019 — 9:00 AM EDT

## Geometry Working Seminar

Ragini Singhal, Department of Pure Mathematics, University of Waterloo

"Deformations of Nearly G_2 instantons - Part 2"

In this talk we will discuss the deformation theory for instantons on  seven-manifolds with nearly parallel G_2-structure of type-I. We will see how the space of perturbations of instantons can be identified with the eigenspaces of the Dirac operatior, which can be used to prove that all the irreducible instantons with semisimple structure group are rigid.

MC 5413

Monday, March 11, 2019 — 4:00 PM EDT

## Pure Math Colloquium

Ellen Kirkman, Wake Forest University

"The Invariant Theory of Artin-Schelter Regular Algebras"

Friday, March 8, 2019 — 3:00 PM EST

## Analysis Seminar

David R. Pitts, University of Nebraska-Lincoln

"Cartan Triples"

Cartan MASAs in von Neumann algebras have been well-studied since the pioneering work of Feldman and Moore in the 1970's. The presence of a Cartan MASA in a a given von Neumann algebra $\mathcal{M}$ is useful for understanding the structure of $\mathcal{M}$. Cartan MASAs arise when applying the group measure space construction with a countable group $\Gamma$ acting essentially freely on the measure space $(X,\mu)$.

Thursday, March 7, 2019 — 4:00 PM EST

## Model Theory Seminar

Anton Bernshteyn, Carnegie Mellon University

"Independent sets in algebraic hypergraphs"

Thursday, March 7, 2019 — 12:00 PM EST

## Grad Student Seminar

Brett Nasserden, Department of Pure Mathematics, University of Waterloo

"Quotient singularities"

Singularities of algebraic varieties which are quotients of a vector space by a finite group provide interesting connections between algebraic geometry, representation theory, and group theory.  I will discuss this circle of ideas with a focus on applications to algebraic geometry.

MC 5403

Tuesday, March 5, 2019 — 10:30 AM EST

## o-minimal GAGA Seminar

Brett Nasserden, Department of Pure Mathematics, University of Waterloo

"Definabilization"

Given an affine variety, scheme, or algebraic space defined over the complex numbers one may construct an associated definable analytic space in a functorial manner. With this definabilization functor in hand it becomes possible to compare categories of algebraic coherent sheaves and definable coherent sheaves. We will explain the constructions above and discuss why it is interesting from a geometric perspective.

MC 5479

Tuesday, March 5, 2019 — 9:00 AM EST

## Geometry Working Seminar

Ragini Singhal, Department of Pure Mathematics, University of Waterloo

"Deformations of Nearly G2 Instantons"

In this talk we will discuss the deformation theory for instantons on  seven-manifolds with nearly parallel G2-structure of type-I. We will see how the space of perturbations of instantons can be identified with the eigenspaces of the Dirac operator, which can be used to prove that all the irreducible instantons with semisimple structure group are rigid.

MC 5413

Monday, March 4, 2019 — 4:00 PM EST

## Pure Math Colloquium

Michael Jury, University of Florida

"A Tour of Noncommutative Function Theory"

### March 2019

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