


Mathematics Seminars and Colloquia
4 December 2023 9 December 2023
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Lecture series on algebraic stacks
Monday, 4th December, 11:30 am
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Host: Sudarshan Gurjar
Venue: Ramanujan Hall
Speaker: Nitin Nitsure, TIFR (retd)
Title: Gerbes and their cohomology classes
Abstract: Locally trivial fiber bundles can be described by their transition functions, giving a class in the first Cech cohomology of the structure group. Gerbes can be regarded as a `higher' version of this twisting phenomenon. The local description of a gerbe gives rise to a class in the second Cech cohomology of the base with coefficients in the `band' (lien in French) of the gerbe. This description of the cohomology class of a gerbe is particularly simple when the band is abelian, which is the case we will describe in this talk. The cohomological Brauer class of Azumaya algebra (or of a projective bundle) is an example of such a cohomological class.
Analysis seminar
Monday 4 Dec, 2023, 1:30 pm  2:30 pm
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Venue: Meeting ID: 835 4823 3902, Passcode: 585182
Join Zoom Meeting
https://us06web.zoom.us/j/83548233902?pwd=A9bwLvfOJtpO88Dmzk1di4YaUq37aZ.1
Host: Chandan Biswas
Speaker: Yves Colin de Verdière
Affiliation: Fourier Institute, CNRS, University of Grenoble I
Title: On the spectrum of the Poincaré operator in ellipsoids.
Abstract: The Poincaré equation describes the motion of an incompressible fluid in a domain submitted to a rotation. The associated wave operator is called the "Poincaré operator". If the domain is an ellipsoid, it was observed by several physicists that the spectrum is a pure point with polynomial eigenfields. I will give conceptual proof of this fact and an asymptotic result on the eigenvalues.