Title: The rank of the Eisenstein ideal
Speaker: Carl Wang-Erickson
Speaker Info: Imperial College London
Brief Description:
Special Note:
Abstract:
In his landmark 1976 paper "Modular curves and the Eisenstein ideal", Mazur studied congruences modulo p between cusp forms and an Eisenstein series of weight 2 and prime level N. He proved a great deal about these congruences, and also posed some questions: how big is the space of cusp forms that are congruent to the Eisenstein series? How big is the extension generated by their coefficients? In joint work with Preston Wake, we give an answer to these questions in terms of cup products (and Massey products) in Galois cohomology. We will introduce these products and explain what algebraic number-theoretic information they encode. Time permitting, we may be able to indicate some partial generalizations to square-free level.Date: Monday, October 30, 2017