Northwestern Number Theory Seminar
Fall 2008



The seminar takes place on Mondays, 3:00-3:50PM in Lunt 107.
Campus Maps: Interactive / Printable PDF






Schedule of Talks

Click on title (or scroll down) for the abstract.

September 29
Frank Calegari (Northwestern)
What is an arithmetic group?
October 6
Alex Gamburd (UCSC/Northwestern)
Sum-product, expanders, and sieving
October 13
Ramin Takloo-Bighash (UIC)
Gross-Prasad for GSp(4)
October 20
Matthew Emerton (Northwestern)
Elliptic curves and modular forms
October 27
John Flynn (Northwestern)
Galois groups and the image size of rational maps
November 3
Mark Reeder (Boston College)
Simple supercuspidal representations and simple wild parameters
November 10
Tong Liu (Purdue)
Lattices in semi-stable representations
November 17
Stephen Kudla (Toronto)
Arithmetic cycles for unitary groups
November 24
Fucheng Tan (MIT)
Galois eigenvarieties
December 1
David Helm (UT Austin)
On p-adic families of admissible representations of GL_2(Q_l)






Abstracts



  • Frank Calegari (Northwestern) What is an arithmetic group?

    This will be an introductory talk on some questions and concepts related to the title.

  • Alex Gamburd (UCSC/Northwestern) Sum-product, expanders, and sieving



  • Ramin Takloo-Bighash (UIC) Gross-Prasad for GSp(4)

    The conjectures of Gross and Prasad predict precise branching laws for representations of orthogonal groups when restricted to orthogonal subgroups locally and globally. In this talk I will explain a recent work verifying certain special cases with interesting arithmetic applications. This is joint work with Dipendra Prasad.

  • Matthew Emerton (Northwestern) Elliptic curves and modular forms

    This is an introductory lecture on the connections between the arithmetic of elliptic curves and the theory of modular forms.

  • John Flynn (Northwestern) Galois groups and the image size of rational maps



  • Mark Reeder (Boston College) Simple supercuspidal representations and simple wild parameters

    This talk is about the interaction between Lie groups and local Galois theory. The local Langlands conjecture predicts that irreducible square-integrable representations of a reductive group G over a p-adic field k should be parametrized by certain homomorphisms from the absolute Galois group of k into a complex Lie group LG which is in some sense dual to G. A recent conjecture of Hiraga-Ichino-Ikeda enhances this conjecture to predict the formal degree of the representation in terms of gamma factors of the parameter. A refinement of the H-I-I prediction leads to the simplest examples of the local Langlands conjecture, which (surprisingly) seem to have gone unnoticed until now. This is joint work with Benedict Gross.

  • Tong Liu (Purdue) Lattices in semi-stable representations

    Let p be an odd prime. We construct and study integral (torsion) p-adic Hodge data, such as Weil-Deligne representation, associated to integral (torsion) semi-stable representations. As an application, we prove the compatibility between local Langlands correspondence and Fontaine's construction at p for Galois representations attached to Hilbert modular forms.

  • Stephen Kudla (Toronto) Arithmetic cycles for unitary groups

    In this talk, I will discuss some recent work with M. Rapoport on arithmetic cycles for Shimura varieties associated to U(n-1,1). In particular, we establish a relation between the arithmetic degrees of certain 0-cycles and the nonsingular, nondegenerate Fourier coefficients of the derivatives of certain incoherent Eisenstein series on U(n,n).

  • Fucheng Tan (MIT) Galois eigenvarieties

    I generalize Kisin's construction of Galois theoretic eigencurve on GL_2(Q) to GL_N and GSp_{2g} over arbitrary number fields. A criterion for smoothness of de Rham points in a Galois eigenvariety and a lower bound of dimension of the eigenvariety will be given. Time permitting, I will prove (in many cases) the de Rhamness of Galois representations attached to Siegel modular forms of low weight and modular forms on GL_2 over imaginary quadratic fields.

  • David Helm (UT Austin) On p-adic families of admissible representations of GL_2(Q_l)

    The local Langlands correspondence for GL_2 associates an admissible representation of GL_2(Q_l) to every Frobenius-semisimple two-dimensional representation of the Weil group W of Q_l. It is an interesting question to try to extend this correspondence to p-adic families of representations of W- that is, given a p-adic family of representations of W, construct a corresponding family of admissible representations of GL_2(Q_l). Recent work of Emerton gives a set of properties that uniquely characterise such a family. We show how to construct such families using deformation-theoretic arguments.