Noncommutative Geometry

Speaker: Magdalena Georgescu (University of Victoria)

"Spectral flow: An introduction I"

Time: 14:30

Room: MC 108

In the context of B(H) (the set of bounded operators on a separable Hilbert space), the spectral flow counts the net number of eigenvalues which change sign as one travels along a path of self-adjoint Fredholm operators. The ability to calculate the spectral flow allows one to calculate the Fredholm index of some operators, making it of interest in the study of non-commutative geometry. It is possible to generalize the concept of spectral flow to a semifinite von Neumann algebra, as we can use a trace on the algebra to measure the amount of spectrum which changes sign. During the course of the two talks, I will start by giving a detailed introduction to spectral flow (for both bounded and unbounded operators), followed by an overview of some important results for the B(H) case, including a characterization of spectral flow due to Lesch, integral formulas for spectral flow, and geometric interpretations (e.g. spectral flow as an intersection number). I will give sketches of some of the more illuminating proofs, and conclude by discussing some of the changes required for the generalization to semifinite von Neumann algebras.

Geometry and Topology

Speaker: Kirill Zaynullin (Ottawa)

"Oriented cohomology of projective homogeneous spaces"

Time: 15:30

Room: MC 107

Oriented cohomology theories and the associated formal groups laws have been a subject of intensive investigations since 60's, mostly inspired by the theory of complex cobordism. In the present talk we discuss several recent developments in the study of algebraic analogues of such theories, e.g. algebraic cobordism of Levine-Morel or algebraic elliptic cohomology, of projective homogeneous spaces.

Analysis Seminar

Speaker: Tatyana Barron (Western)

"Line bundles and automorphic forms"

Time: 15:30

Room: MC 108

I will explain how automorphic forms appear in quantization of compact Riemann surfaces, or, in higher dimensions, quotients of bounded symmetric domains (e.g. ball quotients). I will mention some of my results on explicit construction of automorphic forms as Poincare series. After that I will briefly mention some results from my two papers with N. Askaripour and will pose a few related questions, hoping that maybe someone in the audience will have comments or suggestions.

Noncommutative Geometry

Speaker: Magdalena Georgescu (University of Victoria)

"Spectral flow: An introduction II"

Time: 14:30

Room: MC 108

In the context of B(H) (the set of bounded operators on a separable Hilbert space), the spectral flow counts the net number of eigenvalues which change sign as one travels along a path of self-adjoint Fredholm operators. The ability to calculate the spectral flow allows one to calculate the Fredholm index of some operators, making it of interest in the study of non-commutative geometry. It is possible to generalize the concept of spectral flow to a semifinite von Neumann algebra, as we can use a trace on the algebra to measure the amount of spectrum which changes sign. During the course of the two talks, I will start by giving a detailed introduction to spectral flow (for both bounded and unbounded operators), followed by an overview of some important results for the B(H) case, including a characterization of spectral flow due to Lesch, integral formulas for spectral flow, and geometric interpretations (e.g. spectral flow as an intersection number). I will give sketches of some of the more illuminating proofs, and conclude by discussing some of the changes required for the generalization to semifinite von Neumann algebras.

Homotopy Theory

Speaker:

"Talk CANCELED"

Time: 14:30

Room:

We will resume next week.

Colloquium

Speaker: Alex Buchel (Western)

"Localization and holography in N=2 gauge theories"

Time: 15:30

Room: MC 107

Gauge theory/string theory correspondence maps dynamics of strongly coupled gauge theories to that of the classical supergravity. We describe a highly non-trivial check of the correspondence in the context of Seiberg-Witten models. Specifically, using localization techniques, the path-integral of N=2 supersymmetric SU(Nc) gauge theory can be computed exactly by reducing it to a certain matrix model. In the large-Nc limit the saddle point of the matrix integral picks a particular point on the Coulomb branch of the moduli space. We show that precisely the same point is picked out by the dual gravitational description of the theory. We comment on supersymmetric Wilson loops and the free energy of the theory.

Algebra Seminar

Speaker: Johannes Middeke (Western)

"TBA"

Time: 14:30

Room: MC 107