The Department of Mathematics will be holding a posthumous degree award ceremony for

Yuri Cher

on Tuesday, March 28, 2017
at
10:30 a.m.

in

BA6183
40 St. George St.

~
Everyone is welcome to attend.  Refreshments will be served in the Graduate Lounge.

Yuri Cher memorial invitation

Everyone is welcome to attend.  Refreshments will be served in the Math Lounge before the exam.

Friday, March 24, 2017
4:10 p.m.
BA6183

PhD Candidate:  Benjamin Schachter
Supervisor:  Almut Burchard
Thesis title:  An Eulerian Approach to Optimal Transport with Applications to the Otto Calculus

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Abstract:

This thesis studies the optimal transport problem with costs induced by Tonelli Lagrangians. The main result is an extension of the Otto calculus to higher order functionals, approached via the Eulerian formulation of the optimal transport problem. Open problems 15.11 and 15.12 from Villani’s Optimal Transport: Old and New are resolved. A new class of displacement convex functionals is discovered that includes, as a special case, the functionals considered by Carrillo-Slepčev. Improved and simplified proofs of the relationships between the various formulations of the optimal transport problem, first seen in Bernard-Buffoni and Fathi-Figalli, are given. Progress is made towards developing a rigourous Otto calculus via the DiPerna-Lions theory of renormalized solutions. As well, progress is made towards understanding general Lagrangian analogues of various Riemannian structures.

A copy of the thesis can be found here: DraftThesisSchachter

Memorial Service for Yuri Cher

The Department of Mathematics will hold a Memorial Service for our late graduate student, Yuri Cher, on Tuesday, March 28, 2017 at 10:30 a.m. in the Math lounge.

A remembrance book will be available in the main office the week of March 20.

We look forward to having you join us.

Everyone is welcome to attend.  Refreshments will be served in the Math Lounge before the exam.

Tuesday, April 25, 2017
2:10 p.m.
BA6183

PhD Candidate:  Yiannis Loizides
Supervisor:  Eckhard Meinrenken
Thesis title:  Norm-square localization for Hamiltonian LG-spaces

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Abstract:

A copy of the thesis can be found here:

Everyone is welcome to attend.  Refreshments will be served in the Math Lounge before the exam.

Thursday, February 23, 2017
2:10 p.m.
BA6183

PhD Candidate:  Jack Klys
Supervisor:  Jacob Tsimerman
Thesis title: Statistics of class groups and related topics

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Abstract:

We prove several results concerning class groups of number fields and function fields.

Firstly we compute all the moments of the $p$-torsion in the first step of a filtration of the class group defined by Gerth \cite{gerthprank} for cyclic number fields of degree $p$, unconditionally for $p=3$ and under GRH in general. We show that it satisfies a distribution which Gerth conjectured as an extension of the Cohen-Lenstra-Martinet conjectures. In the $p=3$ case this gives the distribution of the $3$-torsion of the class group modulo the Galois invariant part. We follow the strategy used by Fouvry and Kl$\ddot{\text{u}}$ners in their proof of the distribution of the $4$-torsion in quadratic fields \cite{fk1}.

Secondly, we compute all the moments of a normalization of the function which counts unramified $H_{8}$-extensions of quadratic number fields, where $H_{8}$ is the quaternion group of order $8$, and show that the values of this function determine a constant distribution. Furthermore we propose a similar modification to the non-abelian Cohen-Lenstra heuristics for unramified $G$-extensions of quadratic fields for several other 2-groups $G$, which we conjecture will give finite moments which determine a distribution. These are all cases in which the unnormalized average is known or conjectured to be infinite. Our method additionally can be used to determine the asymptotics of the unnormalized counting function, which we also do for unramified $H_{8}$-extensions. This part of the thesis is joint work with Brandon Alberts.

Thirdly we present several new examples of reflection principles which apply to both class groups of number fields and picard groups of of curves over $\mathbb{P}^{1}/\mathbb{F}_{p}$. This proves a conjecture of Lemmermeyer \cite{franz1} about equality of 2-rank in subfields of $A_{4}$, up to a constant not depending on the discriminant in the number field case, and exactly in the function field case.  More generally we prove similar relations for subfields of a Galois extension with group $G$ for the cases when $G$ is $S_{3}$, $S_{4}$, $A_{4}$, $D_{2l}$ and $\mathbb{Z}/l\mathbb{Z}\rtimes\mathbb{Z}/r\mathbb{Z}$.  The method of proof uses sheaf cohomology on 1-dimensional schemes, which reduces to Galois module computations.

A copy of the thesis can be found here: klysthesis

Everyone is welcome to attend.  Refreshments will be served in the Math Lounge before the exam.

Tuesday, April 25th, 2017
11:10 a.m.
BA6183

PhD Candidate:  James Mracek
Supervisor:  Lisa Jeffrey/ Clifton Cunningham
Thesis title:

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Abstract:

A copy of the thesis can be found here:

Everyone is welcome to attend.  Refreshments will be served in the Math Lounge before the exam.

Friday, February 10, 2017
10:10 a.m.
BA1210

PhD Candidate:  Jeremy Lane
Supervisor:  Yael Karshon
Thesis title:  On the topology of collective integrable systems

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Abstract:

This thesis studies the topological properties of momentum maps of a large family of completely integrable systems called collective completely integrable systems.

The first result concerns the topological monodromy of a collective completely integrable system on a product of three two-spheres. This system is called a “Heisenberg spin-chain” for its connection with a quantum integrable system of the same name.

The remainder of the thesis is concerned with collective systems that are “constructed by Thimm’s trick” with the “action coordinates of Guillemin and Sternberg.”  We observe that the open dense subset of a symplectic manifold where such systems define a Hamiltonian torus action is connected. This observation was absent from the literature until this point. We also prove that if a system is constructed in this manner from a chain of Lie subalgebras then the image is given by an explicit set of inequalities called branching inequalities.

When the symplectic manifold in question is a multiplicity free Hamiltonian $U(n)$-manifold, the construction of Thimm’s trick with the action coordinates of Guillemin and Sternberg yields a completely integrable Hamiltonian torus action on a connected open dense subset. If the momentum map is proper, then we are able to prove lower bounds for the Gromov width of the symplectic manifold  from the classification of the connected open dense subset as a non-compact symplectic toric manifold. Convex multiplicity free manifolds of compact Lie groups have been classified by (Knop, 2010) and (Losev, 2009) and, accordingly, our lower bounds are given in terms of the combinatorics of the classifying data: the momentum set and a lattice. This result is the first estimate for the Gromov width of general multiplicity free manifolds of a nonabelian group.

This result  relies crucially on connectedness of the open dense subset and the explicit description of the momentum map image. The proof is a generalization of methods used to prove lower bounds for the Gromov width of $U(n+1)$ coadjoint orbits (Pabiniak, 2014)  which are an example of multiplicity free $U(n)$-manifolds.

A copy of the thesis can be found here: ut-thesis-revised-March-9

Everyone is welcome to attend.  Refreshments will be served in the Math Lounge before the exam.

Wednesday, February 1, 2017
3:10 p.m.
BA6183

PhD Candidate:  Asif Zaman
Supervisor:  John Friedlander
Thesis title:  Analytic estimates for the Chebotarev Density Theorem and their applications

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Abstract:

In this thesis, we study the distribution of prime ideals within the Chebotarev Density Theorem. The theorem states that the Artin symbols attached to prime ideals are equidistributed within the Galois group of a given Galois extension.

We exhibit field-uniform unconditional bounds with explicit constants for the least prime ideal in the Chebotarev Density Theorem, that is, the prime ideal of least norm with a specified Artin symbol. Moreover, we provide a new upper bound for the number of prime ideals with a specified Artin symbol which is valid for a wide range and sharp, short of precluding a putative Siegel zero. To achieve these results, we establish explicit statistical information on the zeros of Hecke L-functions and the Dedekind zeta function. Our methods were inspired by works of Linnik, Heath-Brown, and Maynard in the classical case and the papers of Lagarias–Odlyzko, Lagarias–Montgomery–Odlyzko, and Weiss in the Chebotarev setting.

We include applications for primes represented by certain binary quadratic forms, congruences of coefficients for modular forms, and the group structure of elliptic curves reduced modulo a prime. In particular, we establish the best known unconditional upper bounds for the least prime represented by a positive definite primitive binary quadratic form and for the Lang–Trotter conjectures on elliptic curves.

A copy of the thesis can be found here: thesis_Zaman_v1

Report: ThesisReport-Zaman

Everyone is welcome to attend.  Refreshments will be served in the Math Lounge before the exam.

Wednesday, February 1, 2017
2:10 p.m.
BA6183

PhD Candidate:  Jerrod Smith
Supervisor:  Fiona Murnaghan
Thesis title:  Construction of relative discrete series representations for $p$-adic $\mathbf{GL}_n$

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Abstract:

Let $F$ be a nonarchimedean local field of characteristic zero and odd residual characteristic.  Let $G$ be the $F$-points of a connected reductive group defined over $F$ and let $\theta$ be an $F$-rational involution of $G$.  Define $H$ to be the closed subgroup of $\theta$-fixed points in $G$.
The quotient variety $H \backslash G$ is a $p$-adic symmetric space.  A fundamental problem in the harmonic analysis on $H \backslash G$ is to understand the irreducible subrepresentations of the right-regular representation of $G$ acting on the space $L^2(H\backslash G)$ of complex-valued square integrable functions on $H\backslash G$.  The irreducible subrepresentations of $L^2(H\backslash G)$ are called relative discrete series representations.

In this thesis, we give an explicit construction of relative discrete series representations for three $p$-adic symmetric spaces, all of which are quotients of the general linear group.  We consider $\mathbf{GL}_n(F) \times \mathbf{GL}_n(F) \backslash \mathbf{GL}_{2n}(F)$, $\mathbf{GL}_n(F) \backslash \mathbf{GL}_n(E)$, and $\mathbf {U}_{E/F} \backslash \mathbf{GL}_{2n}(E)$, where $E$ is a quadratic Galois extension of $F$ and $\mathbf {U}_{E/F}$ is a quasi-split unitary group.  All of the representations that we construct are parabolically induced from $\theta$-stable parabolic subgroups admitting a certain type of Levi subgroup.  In particular, we give a sufficient condition for the relative discrete series representations that we construct to be non-relatively supercuspidal.  Finally, in an appendix, we describe all of the relative discrete series of $ \mathbf{GL}_{n-1}(F)\times  \mathbf{GL}_{1}(F) \backslash  \mathbf{GL}_{n}(F)$.

A copy of the thesis can be found here: thesis_jmsmith-27-01-2017

Funeral service for Yuri Cher

Monday, October 24, 2016

York Cemetery and Funeral Centre
160 Beecroft Rd, North York
ON M2N 5Z5

Visitation: 11:00 a.m.-12:00 p.m.

Service: 12:00 – 1:00 p.m.

Burial: 1:00 p.m.