Geometry and Topology

Speaker: Steven Rayan (Toronto)

"Star-shaped quivers, hyperpolygons, and Higgs bundles"

Time: 15:30

Room: MC 107

I will discuss three closely-related moduli problems: moduli of representations of star-shaped quivers, moduli of hyperpolygons, and moduli of parabolic Higgs bundles. One theme that weaves these three problems together is complete integrability. I will discuss recent results on the topology of these moduli spaces (joint work with Jonathan Fisher) and then pose questions on the relationship between stability for Higgs bundles and stability for hyperpolygons.

Noncommutative Geometry

Speaker: (Western)

" Feynman's Theorem II "

Time: 11:30

Room: MC 107

This is a quick survey of Feynman's asymptotic formula for m-point functions as a sum over graphs.

Homotopy Theory

Speaker: Karol Szumilo (Western)

"Formalized Homotopy Theory (part 3)"

Time: 13:30

Room: MC 107

I will present formal proofs of selected results discussed in preceding seminar talks using the Coq library UniMath.

Colloquium

Speaker: Farzad Fathizadeh (California Institute of Technology)

"Modular forms in gravitational instantons"

Time: 15:00

Room: MC 108

In a succession of papers, physicists and mathematicians have achieved an explicit parameterization of Bianchi-IX gravitational instantons in terms of theta functions with characteristics. By exploiting the latter, in this talk, I will shed light on a rationality phenomena in the spectral action of SU(2)-invariant Bianchi-IX metrics. This will be done by showing that for the instantons, each term in the expansion of their spectral action gives rise to a modular form of weight 2 that can be written explicitly in terms of well-known modular forms, namely the Eisenstein series and the modular discriminant. An elegant proof of the rationality result will also be presented, which is based on expressing Seeley-de Witt coefficients as noncommutative residues of Laplacians. This talk is based on joint works with Wentao Fan and Matilde Marcolli.

Geometry and Combinatorics

Speaker: Jianing Huang (Western)

"Equivariant de Rham theory: from Weil model to Cartan model (part III)"

Time: 16:00

Room: MC 105C

For a smooth manifold M with a Lie group G action, we can define equivariant cohomology based on differential forms on M. That is Weil model. This construction is analogous to Borel construction on the level of differential forms. The Cartan model is then derived from the Weil model. The Cartan model provides an explicit way to compute equivariant cohomology. We will introduce both models and prove that they are equivalent.

This is the third and final part of this talk.

Noncommutative Geometry

Speaker: Rui Dong (Western)

"Classification of Finite Real Spectral Triples III"

Time: 11:30

Room: MC 107

In this talk, I will introduce the structure of finite real spectral triple first, and then I will focus on how to encode those data of a finite real spectral triple inside the so-called "Krajewski diagram".

Algebra Seminar

Speaker: Good Friday

"(No Seminar) "

Time: 16:00

Room: MC 107