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Abstracts for Number theory lunch seminar

Alternatively have a look at the program.

Dimension formulas for vector-valued Hilbert modular modular forms

Posted in
Speaker: 
Fredrik Strömberg
Zugehörigkeit: 
MPI
Datum: 
Don, 2012-12-20 10:45 - 11:45
Location: 
MPIM Lecture Hall

I will present some theoretical and computational aspects of dimension formulas for vector-valued Hilbert modular forms of integral and half-integral weight.

Applications of Number Theory to Wireless Communcations: Units Groups, Quaternion Algebras, and Dedekind Zeta Functions

Posted in
Speaker: 
Dave Karpuk
Zugehörigkeit: 
z.Z. MPI
Datum: 
Mon, 2013-01-28 16:30 - 17:30
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

Research done by information theorists over the past decade has
shown that lattices constructed from rings of integers in number fields,
and orders in division algebras, provide codebooks well-suited for
communication over wireless channels.  In particular, recent work has shown
that when communication over a wireless channel occurs in the presence of
an eavesdropper, one can estimate the eavesdropper's probability of
correctly intercepting the message, using the regulator and Dedekind zeta

On the Fourier coefficients of meromorphic Jacobi forms

Posted in
Speaker: 
René Olivetto
Zugehörigkeit: 
Köln
Datum: 
Mit, 2013-01-30 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar
It is a well known fact that a holomorphic Jacobi form $\phi$ splits into the so called theta--decomposition, and that the associated theta coefficients (essentially the Fourier coefficients of $\phi$) are modular forms. Although a similar decomposition is not possible if $\phi$ is meromorphic, in their recent paper Dabholkar, Murthy, and Zagier extended this construction providing a canonical decomposition of $\phi$, defining the so called canonical Fourier coefficients of $\phi$, and describing their modular property in the case of poles of order at most 2.

Arithmetic aspects of short random walks

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Speaker: 
Armin Straub
Datum: 
Mit, 2013-02-13 14:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

We revisit a classical problem: how far does a random walk travel in a given
number of steps (of length 1, each taken along a uniformly random direction)?
Although such random walks are asymptotically well understood, surprisingly
little is known about the exact distribution of the distance after just a few
steps.  For instance, the average distance after two steps is (trivially)
given by 4/pi; but what is the average distance after three steps?

In this talk, we therefore focus on the arithmetic properties of short random

On the arithmetic of pseudo-reductive and wound unipotent groups

Posted in
Speaker: 
Cristian D. Gonzáles-Avilés (U. de la Serena/MPI)
Datum: 
Mit, 2013-02-20 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

Let k be a global function field. It is a well-known fact that
the first cohomology set of a reductive group over k has an abelian group
structure. In this talk we will show that the first cohomology set of an
arbitrary pseudo-reductive group over k can be naturally embedded in an
abelian group. Under a certain condition, the set in question has a natural
abelian group structure. We will also discuss class groups of wound
unipotent groups of toric type.

Differentiability of Fourier Series related to Eisenstein series ( Please note date and time!)

Posted in
Speaker: 
Izabela Petrykiewicz
Zugehörigkeit: 
U of Grenoble
Datum: 
Fre, 2013-03-01 11:15 - 12:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

In my talk, I will discuss the differentiability of Fourier Series of
the form

F_k(\tau)=\sum_{n=1}^{\infty}\sigma_{k-1}(n) n^{-k-1}e^{2\pi i n \tau} for k even.

These series are related to Eisenstein Series. Using modular (and
quasi-modular) properties of Eisenstein Series, we can find functional
equations for F_k, from which we can draw some conclusions on
differentiability of F_k. This approach was introduced by Itatsu in
1981 in a paper on Differentiability of Riemann's Function.

A Compatible System of Galois Representations

Posted in
Speaker: 
Abhijit Laskar
Zugehörigkeit: 
MPI
Datum: 
Mit, 2013-03-06 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

We will study a system of Galois representations associated to algebraic varieties,
with values in an algebraic group. In particular we will focus on questions of rationality
and l-independence.

Calculation of Riemann's zeta function via interpolating determinants

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Speaker: 
Yuri Matiyasevich
Zugehörigkeit: 
Steklov Inst.
Datum: 
Fre, 2013-03-15 11:15 - 12:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

Using intensive computer calculations, the author empirically discovered
unusual methods for calculating high-precision approximations to the non-trivial zeroes
of Riemann's zeta function, its values and values of its derivative on the whole
complex plane. So far no theoretical explanation to these phenomena is known.

The p-adic monodromy group of abelian varieties over global function fields of characteristic p

Posted in
Speaker: 
Ambrus Pal
Zugehörigkeit: 
Imperial College London
Datum: 
Mit, 2013-04-10 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

We prove an analogue of the Tate isogeny conjecture and the semi-simplicity conjecture for overconvergent crystalline Dieudonne modules of abelian varieties defined over global function fields of characteristic p, combining methods of de Jong and Faltings. As a corollary we deduce that the monodromy groups of such overconvergent crystalline Dieudonne modules are reductive, and after base change to the field of complex numbers they are the same as the monodromy groups of Galois representations on the corresponding l-adic Tate modules, for l different from p.

Finite Quadratic Modules and Weil Representations over Number Fields

Posted in
Speaker: 
Hatice Boylan
Zugehörigkeit: 
MPI
Datum: 
Mit, 2013-04-24 14:15 - 15:15
Location: 
MPIM Lecture Hall
Parent event: 
Number theory lunch seminar

In the study of Hilbert, Jacobi and orthogonal modular forms
of low weight over number fields it is essential to understand the
representations of Hilbert modular groups or of certain two-fold
central extensions. In the case of the field of natural numbers it is
known that the key to the study of all representations of the modular
group $SL(2,Z)$ which are interesting in the mentioned context are
the Weil representations associated to finite quadratic modules. In
analogy to the case of the field of rational numbers we developed a

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