Northwestern Number Theory Seminar
Fall 2009



The seminar takes place on Mondays, 3:00-3:50PM in Lunt 107.
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Previous terms: Fall 2008 / Winter 2009 / Spring 2009





Schedule of Talks

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

September 28
Matthew Emerton (Northwestern)
An introduction to the mod p and p-adic Langlands program for GL_2
October 5
Pierre Colmez (Ecole Polytechnique)
On the p-adic Langlands correspondence for GL_2(Q_p)
October 12
Ellen Eischen (Northwestern)
p-adic differential operators on automorphic forms and applications
October 19
Teruyoshi Yoshida (Cambridge)
Converse of the weight-monodromy conjecture
October 26
Bei Zhang (Northwestern)
p-adic L-function of supersingular Hilbert modular form
November 2
Nick Ramsey (DePaul)
Euclidean Ideal Classes
November 9
David Savitt (Arizona)
Lifting local Galois representations
November 16, 2pm
Florian Herzig (Northwestern)
The classification of irreducible mod p representations of a p-adic GL_n
November 16, 3pm
Sug Woo Shin (Chicago)
Plancherel density theorem
November 30
Joël Bellaïche (Brandeis)
Critical p-adic L-functions
December 3
Toby Gee (Harvard)
The Sato-Tate conjecture for Hilbert modular forms






Abstracts



  • Matthew Emerton (Northwestern) An introduction to the mod p and p-adic Langlands program for GL_2

    I will give an introduction to some parts of the mod p and p-adic Langlands program for GL_2. The focus will be on motivation and simple examples. I will get as far as time permits (which may not be very far).

  • Pierre Colmez (Ecole Polytechnique) On the p-adic Langlands correspondence for GL_2(Q_p)

  • Ellen Eischen (Northwestern) p-adic differential operators on automorphic forms and applications

    At certain special points, the values of the Riemann zeta function and many other L-functions are algebraic, up to a well-determined transcendental factor. G. Shimura, H. Maass, and M. Harris extensively studied a class of differential operators on automorphic forms; these differential operators play an important role in proofs of algebraicity properties of many L-functions. Building on work of N. Katz, we introduce a p-adic analogue of these differential operators, which should be similarly significant in the study of many p-adic L-functions, in particular p-adic L-functions attached to families of p-adic automorphic forms on unitary groups.

  • Teruyoshi Yoshida (Cambridge) Converse of the weight-monodromy conjecture

    This is an expository talk on (classical) global/local Langlands correspondence between Galois representations and automorphic/smooth representations of GL(n). The long-standing weight-monodromy conjecture claims that all geometric local Galois representations (i.e. appearing in etale cohomology of varieties) are pure, but we can show that all pure local Galois representations are found in geometry. It seems that we can only do this via global argument (Honda-Tate theory etc), and we introduce Langlands correspondence in the course of going through several proofs.

  • Bei Zhang (Northwestern) p-adic L-function of supersingular Hilbert modular form

    Pollack constructed p-adic L-function of modular form f at supersingular primes. Especially, when the Fourier coefficient of f at p is zero, plus and minus p-adic L-functions can be obtained as elements inside Iwasawa algebra. They can serve as one side of Iwasawa main conjecture for an elliptic curve over Q when a_p=0 by Kobayashi's work about +/- Selmer group of this elliptic curve at p. As the generalization of Pollack's work, I will discuss the construction of p-adic L-function for supersingular Hilbert modular form using Rankin-Selberg method. And will define the +/- p-adic L-functions in this case.

  • Nick Ramsey (DePaul) Euclidean Ideal Classes

    In the 1970's, Lenstra generalized the notion of a Euclidean ring to that of a ring with a Euclidean ideal. In the context of Dedekind domains, the consequence of the existence of such an ideal is the cyclicity of the class group in much the same way that the consequence of the existence of a Euclidean algorithm is the triviality of the class group. In this talk, I'll discuss Lentra's notion in light of some recent developments of Hester Graves. In particular, I'll discuss a joint result with Graves classifying the quadratic imaginary fields (which play a rather exception role in the theory) that have a Euclidean ideal.

  • David Savitt (Arizona) Lifting local Galois representations

    I will explain the proof of some cases of the weight part of Serre's conjecture over totally real fields. One key ingredient is the construction and study of certain lifts of mod p Galois representations, and this will be the focus of the talk. This is joint work with Toby Gee.

  • Florian Herzig (Northwestern) The classification of irreducible mod p representations of a p-adic GL_n

    Let F be a finite extension of the p-adic numbers. We describe the classification of irreducible admissible smooth representations of GL_n(F) over an algebraically closed field of characteristic p, in terms of "supersingular" representations. This generalizes results of Barthel-Livne for n = 2. Our motivation is the hypothetical mod p Langlands correspondence for GL_n, which is supposed to relate smooth mod p representations of GL_n(F) to n-dimensional mod p Galois representations.

  • Sug Woo Shin (Chicago) Plancherel density theorem

    Serre asked and answered the following question: Fix a prime p. Consider the eigenvalues of the Hecke operator T_p on the space of cuspforms of weight k and level N, where (p,N)=1. What is the distribution of the eigenvalues as k and/or N tend to infinity? The answer turns out to be the Plancherel measure. First I will review the Plancherel measure in the context of harmonic analysis on p-adic (and real) Lie groups. Next I will interpret, reformulate and generalize Serre's question to the case of arbitrary reductive groups over Q. (Serre's situation is concerned with the case G=GL_2. When G is anisotropic over Q, this result is due to Sauvageot.)

  • Joël Bellaïche (Brandeis) Critical p-adic L-functions

    For three decades, it was only possible to attach a p-adic L-function to a cuspidal eigenform of weight k whose slope (that is, p-valuation of the eigenvalue for the operator U_p) was strictly less than k+1. More recently, Stevens and Pollack explained how to attach, in a natural way, a p-adic L-function for some slope k+1 (or critical slope) cuspidal eigenforms, namely the cuspidal forms that are not critical. I shall explain how, using our knowledge of the geometry of the eigencurve, one can extend their work and define natural p-adic L-functions for the missing cuspidal eigenforms as well as for the evil Eisenstein series. I shall also show that all those p-adic L-functions, old and new, fit in a two-variables p-adic L-function on the eigencurve, extending earlier results of Stevens, Panchishkin and Emerton.

  • Toby Gee (Harvard) The Sato-Tate conjecture for Hilbert modular forms

    I will discuss the Sato-Tate conjecture for Hilbert modular forms, which I recently proved in collaboration with Thomas Barnet-Lamb and David Geraghty. No previous knowledge of Hilbert modular forms or the Sato-Tate conjecture will be assumed.