Speaker: Kathleen Petersen
Title: Cusps and Congruence Subgroups
Affiliation: Queen's University, Canada
Date: Monday, February 4, 2008
Place and Time: Room 102, Love Building, 3:35-4:30 pm

Abstract. It is a classical result of Petersson's that the existence of non-congruence subgroups in PSL(2,Z) can be seen topologically by counting cusps. I'll discuss the generalization of this to PSL(2,A), where A is the ring of integers of a number field. This has a surprising connection to Artin's primitive root conjecture.