Type: Seminar

Modified: Tue 17 Oct 2023 1122

Distribution: World

Expiry: 19 Oct 2023

CalTitle1: SMRI Seminar: Treumann - ’Deligne-Lusztig varieties or irregular connections’ (in-person only)

Auth: hannahb@w1d4n6z2.staff.sydney.edu.au (hbry8683) in SMS-SAML

**Please note this seminar is in-person only SMRI Seminar: ’Deligne-Lusztig varieties or irregular connections’ David Treumann (Boston College) Thursday 19 October 1:00-2:00pm (AEDT) Carslaw 375 Abstract: I will give an introduction to Deligne-Lusztig theory, and a second introduction to the theory of irregular singularities of linear ODEs, and make some comparisons. Deligne-Lusztig theory organizes most of the irreducible characters of a finite group G of Lie type of into "series," that are indexed by conjugacy classes of maximal abelian subgroups T of G. The representations in one series are those that appear in the cohomology of an F_p-bar-variety X equipped with an action of the finite group G x T. A basic result of Deligne and Lusztig is "orthogonality", which tells e.g. that representations in the series corresponding to T are different from representations in the series corresponding to T-prime, when T is not conjugate to T-prime. It is proved by analyzing a stratification of the quotient (X times X-prime)/G. I will explain how the varieties X and (X times X-prime)/G, and this stratification, arise as moduli spaces of constructible sheaves on a topological annulus. They have a lot in common with moduli spaces of connections on C^* with irregular singularities at zero and infinity. ---- Please join us after the seminar for SMRI afternoon tea, 2:00-2:45pm every Thursday on the SMRI Terrace (accessed through A14-04-L4.36) ---- Other upcoming SMRI events can be found here: https://mathematical-research-institute.sydney.edu.au/news-events/ SMRI YouTube Channel: https://youtube.com/@SydMathInst

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