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Abstracts for Number theory lunch seminar

Alternatively have a look at the program.

Euler-Kronecker constants: from Ramanujan to Ihara (partly joint work with Kevin Ford and Florian Luca)

Posted in
Speaker: 
Pieter Moree
Affiliation: 
MPIM
Date: 
Wed, 2011-08-03 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

Zeta functions usually have a pole, say at s=n, and a residue there that
provides a lot of information about the associated object. The next step is
to consider the constant in the Taylor series around s=n. For the Riemann
zeta function
this gives the Euler constant. The ratio of the constant and the residue
is called the Euler-Kronecker
constant. Lately this constant has been intensively studied by
mathematicians such as Y. Ihara,
Kumar Murty and Tsfasman (especially for the Dedekind zeta function of a
cyclotomic number field).

Borcherds Products

Posted in
Speaker: 
Bernhard Heim
Affiliation: 
GUtech Oman/ MPIM
Date: 
Wed, 2011-08-10 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

Infinite products in the sense of Borcherds
have applications in many areas. They appear in the proof the moonshine
conjecture,
in physics (generalized Kac-Moody algebras, string theory), and number
theory.
The construction of Borcherds products is pretty complicated and non-linear.
In this talk we report on recent results [joint work with A. Murase].

Meromorphic continuation of Dirichlet series for CM-periods of automorphic functions on GL(2)

Posted in
Speaker: 
Andre Reznikov
Affiliation: 
Bar-Ilan
Date: 
Wed, 2011-08-10 16:30 - 17:30
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

I consider expansion at a  CM-point for a Hecke-Maass cusp form. This leads
to a collection of (spherical) coefficients analogous to the classical (unipotent)
Fourier coefficients of automorphic functions on GL(2).  These coefficients were
introduced by H. Petersson, and are connected to special values of L-functions
via the theorem of Waldspurger on the torus period. We prove meromorphic
continuation for a  Dirichlet series build from these coefficients. For the Eisenstein

Numerical computation of Maass forms and associated L-functions

Posted in
Speaker: 
Holger Then
Date: 
Wed, 2011-08-17 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

In order to extend the theory of Dirichlet series with Euler products,
Maass studied non-holomorphic automorphic functions, nowadays called Maass
forms.  While the existence of Maass cusp forms is known by the
Roelcke-Selberg spectral resolution, their explicit form can only be
approximated numerically.  We recall the yet most successful algorithm for
approximating Maass forms and explore some of their properties.  Then, we
present an Odlyzko-Schoenhage type algorithm which computes Maass
L-functions high up in the critical strip.
 

Symmetries for automorphic forms on orthogonal groups (joint work with Bernhard Heim)

Posted in
Speaker: 
Atsushi Murase
Affiliation: 
Kyoto Sangyo University
Date: 
Wed, 2011-08-24 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

Borcherds lifts on $G=O(2,n+2)$ are meromorphic automorphic forms
whose divisors are Heegner divisors. In this talk, we discuss on
holomorphic automorphic forms
on  $G$ satisfying certain symmetries. We show that, with an additional
assumption,
these forms are Borcherds lifts. In the cases of $n=0$ and $n=1$, we can
remove this
additional condition and hence Borcherds lifts are characterized by the
symmetries.

The Discrete Fourier Transform (DFT)

Posted in
Speaker: 
Shamgar Gurevich
Affiliation: 
UW Madison
Date: 
Wed, 2011-08-24 16:30 - 17:30
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

The Discrete Fourier Transform (DFT) is one of the most important operators in computational mathematics. The DFT operator acts on the n-dimenional Hilbert Space $L^2(Z/n)$ of complex valued functions on the group of integers modulo n: It becomes very useful in the last century due to the Cooley-Tukey Fast Fourier Transform (FFT) algorithm that computes the DFT in order of nlog(n) operations.

Local Langlands correspondence and exterior and symmetric square root numbers for $GL(n)$

Posted in
Speaker: 
Freydoon Shahidi
Affiliation: 
Purdue
Date: 
Wed, 2011-09-07 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

Let $\rho$ be an $n$-dimensional continuous complex representation of $W'_F$, the Weil-Deligne group of a local field $F$. Denote by $\pi(\rho)$ the irreducible admissible representation of $GL_n(F)$ attached to $\rho$ by the local Langlands correspondence. Let $\Lambda^2$ be the exterior square representation of $GL_n(\Bbb C)$. Let $L(s,\Lambda^2\rho)$ and $\varepsilon(s,\Lambda^2\rho,\psi_F)$ be the Artin $L$-function and root number defined by $\Lambda^2\rho$.

Counting lattice points

Posted in
Speaker: 
Bernhard Krötz
Affiliation: 
U. Hannover
Date: 
Wed, 2011-09-14 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

Introduction to local geometric Langlands

Posted in
Speaker: 
Masoud Kamgarpour
Date: 
Wed, 2011-09-21 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

Local Langlands program predicts a close relationship between
representations of the absolute Galois group of a
local field F and irreducible representations of reductive groups over F. A
geometric version of this program
attempts to relate vector bundles equipped with (flat) connections on the
complex puncture disk to
representations of the affine Kac-Moody algebras. After laying out the
process of going from classical
statements to geometric predictions, I will explain Frenkel-Gaitsgory's
picture in the unramified case. I will

The L^2 restriction of a GL(3) Maass form

Posted in
Speaker: 
Xiaoqing Li
Date: 
Wed, 2011-09-28 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

In this talk, we will study the L^2 restriction problem of a GL(3) Maass form to GL(2).
By Parseval's formula, the problem becomes bounding averages of different families
of GL(3)xGL(2) L-functions. Assuming the Lindelof hypothesis for these
GL(3)xGL(2) L-functions as we usually do, one can achieve a sharp bound in
terms of the analytic conductor of the varying GL(3) Maass form. However,
we will give an unconditional proof of this sharp bound for selfdual GL(3) Maass
forms. For nonselfdual GL(3) Maass forms, our bounds depend on the bounds

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