Event time:

Wednesday, November 17, 2021 - 4:15pm

Speaker:

Vesselin Dimitrov

Speaker affiliation:

University of Toronto

Event description:

Abstract:

It was already known to Klein that the modular group SL_2(Z) has

extraordinarily many finite index subgroups, most of which are not defined

by congruence conditions on the matrix entries. The Unbounded Denominators

conjecture, solved in a recent joint work with Frank Calegari and Yunqing

Tang, is an amendment for the failure of the Congruence Subgroup Property

for SL_2(Z): a Z[[q]] condition on the Fourier expansions of the modular

forms living on a given finite index subgroup of SL_2(Z) turns out to be a

necessary and sufficient condition for the subgroup to be congruence.

Special note:

Meeting ID: 947 9366 7412