Geometry and Topology

Speaker: Dan Christensen (Western)

"Categories of smooth spaces"

Time: 15:30 - 16:30

Room: MC 107

I will describe some categories of "smooth spaces" which generalize the notion of manifold. The generalizations allow us to form smooth spaces consisting of subsets and quotients of manifolds, as well as loop spaces and other function spaces. In more technical language, these categories of smooth spaces are complete, cocomplete and cartesian closed. I will give examples and discuss possible applications.

Analysis Seminar

Speaker: Richard Hind (Notre-Dame)

"Symplectic embeddings and holomorphic curves"

Time: 14:30 - 15:30

Room: MC 107

We obtain a new obstruction to symplectic embeddings derived using the Symplectic Field Theory.

Pizza Seminar

Speaker: Matthias Franz (Western)

"Primes in Cryptography"

Time: 16:30 - 17:30

Room: MC 107

Although we might not be aware of it, Number Theory has entered our daily lives: encrypted Internet connections (e.g., for online banking) are based on algorithms involving giant prime numbers with several hundred or more digits.

In this talk, I will explain how RSA, the most prominent of these public key encryption schemes, works. Then I will address the important question of how one can actually find the large primes needed for these applications. The primality tests used in practice turn out to be probabilistic, which means that they may sometimes give a wrong answer. Hopefully, I will convince you that this is no reason to be worried about the money in your account.

Noncommutative Geometry

Speaker: Ivan Dynov (York University)

"Type III von Neumann algebras associated the infinite-dimensional nilpotent group B_0^\mathbb Z"

Time: 15:00 - 16:30

Room: MC 106

We consider von Neumann algebras generated by regular representations of the infinite-dimensional group B_0^\mathbb Z of infinite, finite-order upper triangular matrices. These regular representations were defined and studied by Alexander Kosyak. They depend on a Gaussian measure on the group of infinite (arbitrary order) upper triangular matrices. A certain condition on the measure implies that the right regular representation is reducible and that the von Neumann algebra generated by the right regular representation is the commutant of the left one. In this case we prove that these von Neumann algebras are type III_1 factors, according to the classification of Alain Connes.

Colloquium

Speaker: Richard Hind (Notre Dame University)

"Symplectomorphisms of products"

Time: 15:30 - 16:30

Room: MC 108

Hamiltonian (or symplectic) diffeomorphisms are well-known to preserve volume. Gromov's work in the eighties implied that the smallest factor in a polydisk also corresponds to an invariant of symplectic embeddings. In dimensions at least 6 we will ask to what extent the areas of other factors place restrictions on symplectic embeddings. Specific constructions will show that any such restrictions must be fairly weak, but they nevertheless exist and remarkably our constructions turn out to be in some sense sharp. We will derive some implications for Hofer's metric on groups of Hamiltonian diffeomorphisms.

Stable Homotopy

Speaker: Peter Oman (Western)

"Enriched Category Theory and Homotopy Theory"

Time: 14:00 - 15:00

Room: MC 107

Algebra Seminar

Speaker: *** joint with NCG Seminar *** Hadi Salmasian (University of Windsor)

"Character sheaves and representations of p-adic groups"

Time: 15:30 - 16:30

Room: MC 106

In this talk we give a geometric interpretation of characters of certain representations of p-adic GL(n), which are usually called depth zero supercuspidal representations, in terms of Euler characteristics of certain character sheaves. Our work relies on Lusztig's theory of character sheaves, and in some sense suggests a general framework for relating character sheaves on groups over a nonarchimedean local field to smooth representations. (Joint with Clifton Cunningham.)

Geometry and Topology

Speaker: Aji Dhillon (Western)

"Non existence of the universal bundle according to Nori"

Time: 15:30 - 16:30

Room: MC 107

A theorem of Ramanan says that there is no universal bundle on any Zariski open subset of the moduli space of stable bundles over a curve. In this talk I will outline a proof of this fact due to Nori. The idea is to restrict a family to an analytic neighbourhood of the trivial bundle. Luna's etale slice theorem comes to the rescue and gives a very concrete description of this analytic neighbourhood which one uses to prove the theorem.

Stable Homotopy

Speaker: Peter Oman (Western)

"Postponed to next week"

Time: 14:00 - 15:00

Room: MC 107

Algebra Seminar

Speaker: David Wehlau (Queen's University)

"TBA"

Time: 14:30 - 14:30

Room: MC 108

Algebra Seminar

Speaker: Eric Schost (Western)

"The search for a secure curve of genus 2"

Time: 15:30 - 16:30

Room: MC 106

The most famous representative of public-key cryptography is the RSA cryptosystem. However, it is now losing its predominance: elliptic curve cryptography is more efficient, in terms of speed and key size.

Using curves of genus 2 may provide systems that are faster than their elliptic analogues. I will describe current efforts to find a "secure" curve of genus 2, and give an overview of the extensive computations involved.

Joint work with Pierrick Gaudry