NTS Spring 2015 Abstract

Jan 29

Lillian Pierce

Averages and moments associated to class numbers of imaginary quadratic fields

Given an imaginary quadratic field of discriminant d, consider the p-part of the associated class number for a prime p. This quantity is well understood for p=2, and significant results are known for p=3, but much less is known for larger primes. One important type of question is to prove upper bounds for the p-part. Desirable upper bounds could take several forms: either “pointwise” upper bounds that hold for the p-part uniformly over all discriminants, or upper bounds for the p-part when averaged over all discriminants, or upper bounds for higher moments of the p-part. This talk will discuss recent results (joint work with Roger Heath-Brown) that provide new upper bounds for averages and moments of p-parts for odd primes.

Feb 05

Keerthi Madapusi

Heights of special divisors on orthogonal Shimura varieties

The Gross-Zagier formula relates two complex numbers obtained in seemingly very disparate ways: The Neron-Tate height pairing between Heegner points on elliptic curves, and the central derivative of a certain automorphic L-function of Rankin type. I will explain a variant of this in higher dimensions. On the geometric side, the intersection theory will now take place on Shimura varieties associated with orthogonal groups. On the analytic side, we will find Rankin-Selberg L-functions involving modular forms of half-integral weight. This is joint work with Fabrizio Andreatta, Eyal Goren and Ben Howard.

Feb 12

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Feb 19

David Zureick-Brown

The canonical ring of a stacky curve

We give a generalization to stacks of the classical theorem of Petri -- i.e., we give a presentation for the canonical ring of a stacky curve. This is motivated by the following application: we give an explicit presentation for the ring of modular forms for a Fuchsian group with cofinite area, which depends on the signature of the group. (The talk will be mostly geometric and will require little understanding of modular forms.) This is joint work with John Voight.

Feb 26

Rachel Davis

Origami and Galois representations

Let E be an elliptic curve over Q. An origami is a pair (C, f), where C is a curve and f : C → E is a map, branched only above one point. When C is E and f is multiplication by n, there is an associated Galois representation (that depends on a rational point P ∈ E) to an affine general linear group. We explain this and then study the Galois theory for origami with non-abelian monodromy groups. This is joint work with Edray Goins.

Mar 05

Hongbo Yin

Some non-congruence subgroups and the associated modular curves

We give some new non-congruence subgroups which is close to the Fermat groups but with very different properties.

Organizer contact information

Sean Rostami (srostami@math.wisc.edu)

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