11.10.2022 20:30 zoom

Zhongkai Tao (UC Berkeley)

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18.10.2022

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25.10.2022

Clemens Weiske -- online

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15.11.2022

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22.11.2022

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29.11.2022

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06.12.2022

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13.12.2022

N.N.

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20.12.2022

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10.01.2023

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17.01.2023

Frédéric Naud (Sorbonne Université, France) -- online

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24.01.2023 Zoom

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31.01.2023

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12.04.2022

Moritz Doll (Bremen)

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Divisor of the Selberg Zeta Function for Hyperbolic Surfaces with Twists

We consider a finitely generated co-compact Fuchsian group $\Gamma$. The quotient $X = \mathbb{H} / \Gamma$ is a geometrically finite hyperbolic surface with infinite area that might have conical singularities. Given a unitary representation $\chi$ of $\Gamma$, we show that the associated Selberg zeta function admits a factorization, which gives a spectral interpretation of its zeros in terms of the resonances of a suitable Laplacian. This generalizes a theorem by Borthwick-Judge-Perry, where a similar factorization was shown for untwisted hyperbolic surfaces without conical singularities. This is based on joint work with Ksenia Fedosova and Anke Pohl.

19.04.2022

Benjamin Hinrichs (Jena)

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In models from quantum physics describing the interaction of a quantum mechanical particle with a quantum field of bosons, one observes the phenomenon of infrared-criticality if the bosons are massless. From the physical perspective, this is attributed to the fact that even tiny energy fluctuations can lead to the creation of an infinite cloud of low-energy bosons. Mathematically, infrared-criticality means that the selfadjoint Hamilton operator describing the system does not have a ground state, i.e., the infimum of its spectrum is not an eigenvalue. In this talk, we will first demonstrate this phenomenon on a toy quantum field theory. After that, we consider the spin boson model, in which the particle interacting with the massless bosonic field is a qubit. We discuss a recent proof that the spin boson model does have a ground state, even in the infrared-critical situation, if the coupling of qubit and field is below a critical value. Heuristically, this is explained by the fact that symmetries of the model can lead to cancellations of infrared-divergences. Our proof combines three ingredients: a compactness argument, a Feynman-Kac-Nelson type formula and a correlation bound for one-dimensional Ising models. The talk is based on joint work with David Hasler and Oliver Siebert.

10.05.2022

Renato Renner (ETH Zürich)

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From Quantum Cryptography to Quantum Gravity

What statements can we make about information that is inaccessible to us? This question arises both in quantum cryptography and in quantum gravity. In the former, we would like to put bounds on the information that an eavesdropper may possess. In the latter, we are interested, for instance, in the information content of a black hole. In this talk I will show how quantum information theory allows us to characterise such inaccessible information. As applications, I will discuss some implications to quantum cryptography and quantum gravity.

17.05.2022

Josh Maglione (Uni Bielefeld)

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24.05.2022

Javier Echevarria Cuesta (Ecole Polytechnique, Paris)

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An algorithm to compute the spectrum of the Laplace-Beltrami operator on hyperbolic surfaces

The eigenvalues and eigenfunctions of the Laplace-Beltrami operator on a given manifold encode a wealth of information; they help us solve inverse problems, the heat equation, the wave equation, and the Schrödinger equation, to name a few applications. It is hence a classical problem to compute them. Without having to look any further, the case of two-dimensional oriented surfaces of constant curvature is already very rich. Indeed, while we fully understand the spectral theory for these manifolds when the curvature is non-negative, the hyperbolic case eludes explicit computations. Here we propose a new algorithm for their rigorous approximation. This is joint work with Alexander Strohmaier.

31.05.2022

NN

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07.06.2022

Krystal Guo (University of Amsterdam) -- Hörsaal D1

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14.06.2022

NN

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21.06.2022

Samuel Edwards (University of Bristol) -- Hörsaal D1

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28.06.2022

Guenda Palmirotta (Luxembourg) -- now ONLINE!

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In the Euclidean case, it is well-known, by Malgrange and Ehrenpreis, that linear differential operators with constant coefficients are solvable. However, what happens, if we genuinely extend this situation and consider systems of linear invariant differential operators, is still solvable? In case of $\mathbb{R}^n$ (for some positive integer $n$), the question has been proved mainly by Hörmander. We will show that this remains still true for Riemannian symmetric spaces of non-compact type $X=G/K$. More precisely, we will present a possible strategy to solve this problem by using the Fourier transform and its Paley-Wiener(-Schwartz) theorem for (distributional) sections of vector bundles over $X$. We will get complete solvability for the hyperbolic plane $\mathbb{H}^2=SL(2, \mathbb{R})/SO(2)$ and beyond.

This work was part of my doctoral dissertation supervised by Martin Olbrich.

05.07.2022

Viet Dang (Institut Math. Jussieu) -- zoom

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Length Orthospectrum between convex bodies on flat tori.

I will describe joint work with Gabriel Rivière and Matthieu Léautaud where we construct new anisotropic Sobolev spaces on cotangent of tori. These spaces are adapted to the study of the transport by the geodesic flow. As an application, we show a new summation formula of Meyer-Guinand type relating the orthogeodesic spectrum between two convex bodies and the spectrum of the magnetic Laplacian on the torus.

06.07.2022

11:15-12:45

Job Kuit (Paderborn) -- Raum J3.330

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The most continuous part of the Plancherel decomposition for a real spherical space

Let Z be a homogeneous space of a real reductive group G. The Plancherel decomposition of Z is the decomposition of the space L^2(Z) of square integrable functions into a direct integral of irreducible unitary representations of G. In general this decomposition has a mixed discrete and continuous nature.
In this talk we consider real spherical homogeneous spaces Z. In particular, we will focus on the most continuous part of L^2(Z), i.e., the closed subspace of L^2(Z)  that decomposes in the largest continuous families. Recently, Eitan Sayag and I finished an article in which we give a precise description of the Plancherel decomposition of the most continuous part. I will discuss some of the ingredients and key ideas that went into this article.

12.07.2022

Norio Konno (Yokohama National University) -- zoom

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19.10.2021

Kein Seminar

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26.10.2021

Lasse Wolf (Universität Paderborn)

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02.11.2021

Mohammad Talebi (Universität Oldenburg)

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Analytic Torsion for manifolds with fibred boundary metrics

The Analytic Torsion was introduced by Daniel Burrill Ray and Isadore M.
Singer as analytic counterpart of R-Torsion from Topology.
In this talk we define the Analytic Torsion for Manifolds with Geometry at
infinity using structure results of Heat kernel in short and long time regimes.
We determine the structure of heat kernel by means of Geometric Microlocal
Analysis in the sense of Melrose et al.

09.11.2021

N.n.

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16.11.2021

Simon Roby (Tsinghua University)

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Resonances of the Laplace operator on homogeneous vector bundles over the real hyperbolic space

We study the resonances of the Laplacian acting on the compactly supported sections of the homogeneous vector bundle over the real hyperbolic space $H^n(\mathbb{R})=G/K$ determined by a representation $\tau$ of the maximal compact $K$ of $G$. We will see how to determine the resonances. Under the additional assumption that $\tau$ occurs in the spherical principal series, we determine the resonance representations. They are all irreducible. We will see how to find their Langlands parameters and their wave front sets. If additional time is available, we will see what are the differences if we replace the real hyperbolic space by others hyperbolic spaces.

23.11.2021

Christian Arends (Universität Paderborn)

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30.11.2021

Damian Osajda (University of Wroclaw)

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Helly graphs and their automorphism groups

A graph is Helly if each family of pairwise intersecting (combinatorial) balls has non-empty intersection. Groups acting geometrically on such graphs are themselves called Helly. The family of such groups is vast, it contains: Gromov hyperbolic groups, CAT(0) cubical groups, Garside groups, FC type Artin groups, and others. On the other hand, being Helly implies many important algorithmic and geometric features of the group. In particular, such groups act geometrically on spaces with convex geodesic bicombing, equipping them with a kind of CAT(0)-like structure. I will present basic properties and examples of Helly groups. The talk is based on joint works with Jeremie Chalopin, Victor Chepoi, Anthony Genevois, Hiroshi Hirai, Jingyin Huang, Motiejus Valiunas, Thomas Haettel.

07.12.2021

Kein Seminar wegen Oberwolfach Workshop

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14.12.2021

Andreas Juhl (Humboldt-Universität Berlin)

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21.12.2021

Antoine Meddane (Université de Nantes)

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11.01.2022

Dominik Brennecken (Universität Paderborn)

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18.01.2022

Philipp Schütte (Universität Paderborn)

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25.01.2022

Anders Karlsson (University of Geneva)

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01.02.2022

Khalid Koufany (Université de Lorraine)

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13.04.2021

NN

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20.04.2021

Corina Ciobotaru (IHÉS)

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Chabauty limits of subgroups of SL(n,Q_p)

For a locally compact group G (e.g. G=SL(n,Q_p)) the set S(G) of all closed subgroups of G is a compact topological space with respect to the Chabauty topology. Given a subset X of S(G) it is natural to ask what is the closure of X in S(G) with respect to the Chabauty topology. In a joint work with Arielle Leitner and Alain Valette we study such closure when X is the set of all SL(n,Q_p)-conjugates of the diagonal Cartan subgroup C of SL(n,Q_p). By using the action of SL(n,Q_p) on its associated Bruhat—Tits building and an explicit, well-behaved, replacement of a Lie functor on the closure of our set X, we are able to give a classification of all the limits of X and to compute all of them (up to conjugacy) when n < 5.                                                                                                     

27.04.2021

Yann Chaubet (Université Paris-Saclay)

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Closed geodesics with prescribed intersection numbers

On a closed negatively curved surface, Margulis gave the asymptotic growth of the number of closed geodesics of bounded length, when the bound goes to infinity. In this talk, we will investigate such a counting result for closed geodesics of which certain intersection numbers (with a given family of pairwise disjoint simple closed geodesics) are prescribed.                                                                                                  

04.05.2021

Léo Bénard (Universität Göttingen)

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Asymptotics of twisted Alexander polynomials and hyperbolic volume

Given a hyperbolic 3-manifold of finite volume M, we compute the asymptotics of the family of twisted Alexander polynomials on the unit circle. We show it grows exponentially as the volume times the square of the dimension of the representation. Joint work with J. Dubois, M. Heusener and J. Porti. The proof goes through the study of the analytic torsion of some compact hyperbolic manifolds obtained by Dehn surgery on M.                                                                                                      

11.05.2021

Quentin Labriet (Université de Reims Champagne-Ardenne)

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Symmetry breaking operators and orthogonal polynomials

Symmetry breaking operators are intertwinning operators for the restriction of an irreducible representation. In some cases, these are given by differential operators whose symbol is related some classical orthogonal polynomials. First, I will  describe the example of the Rankin-Cohen brackets which are symmetry breaking operators for the tensor product of two representation of the holomorphic discrete series of SL2(R). I will explain how they are related to Jacobi polynomials, and to the classical Jacobi transform. In a second part, I will discuss some ongoing work on the restriction for representation of the holomorphic discrete series for the conformal group of a tube domain.                                                                                                      

18.05.2021

NN

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01.06.2021

NN

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08.06.2021

Benjamin Küster (Universität Paderborn)

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Oscillatory integrals in equivariant cohomology

15.06.2021

Jean-Philippe Anker (Universite d'Orleans)

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Let $X=G/K$ be a Riemannian symmetric space of noncompact type, let $\Gamma$ be a discrete torsion free subgroup of $G$, let $Y\=\Gamma\backslash G/K$ be the associated locally symmetric space and let $\Delta$ be the  Laplace-Beltrami operator on $Y$. In rank one, a celebrated result, due to Elstrodt, Patterson, Sullivan and Corlette, expresses the bottom of the $L^2$ spectrum of $-\Delta$ in terms of the critical exponent of the Poincar\'e series of $\Gamma$ on $X$. A less precise result was obtained later on by Leuzinger in higher rank.

We shall discuss in this talk higher rank analogs of the rank one result, which are obtained by considering suitable Poincar\'e series. This is joint work with Hong-Wei Zhang [arXiv:2006.06473].

22.06.2021

Gerhard Keller (Universität Erlangen)

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I plan to start with a brief introduction to B-free dynamical systems (derived from B-free numbers like e.g. the square-free ones). After a short description of the range of dynamical possibilities of these systems, I will concentrate on the two extreme ends of this range, namely on those B-free systems which are "as chaotic as possible" (like the square-free system), and those which are "as close to being periodic as possible" (regular Toeplitz systems). For these two  classes of topological dynamical systems I will report about recent and ongoing progress in understanding the automorphism group of the systems.                                                                                                

29.06.2021

Genkai Zhang (Chalmers University of Technology)

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Branching of metaplectic representation of Sp(n, R) under its principal SL(2, R) subgroup

Any simple split Lie group $G$  has a unique  principal S=SL(2, R) subgroup, by the work of Kostant. We study the branching problem for holomorphic representations  of G=Sp(n, R) under S. A complete decomposition is found for the metaplectic representation of G=Sp(2, R). We use both some classical method of orthogonal polynomials and the geometric tool of Chern connection.                                                                                                     

06.07.2021

Agnieszka Hejna (University of Wroclaw)

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Harmonic analysis in the rational Dunkl setting

Dunkl theory is a generalization of Fourier analysis and special function
theory related to root systems and reflections groups. The Dunkl operators T_j, which were introduced by C. F. Dunkl in 1989, are deformations of directional derivatives by difference operators related to the reflection group. The goal of this talk will be to study harmonic analysis and Hardy spaces in the rational Dunkl setting. The first part will be devoted to two results: improved estimates of the heat kernel h_t(x,y) of the Dunkl heat semigroup generated by the Dunkl--Laplace operator Delta_k=\sum_{j=1}^NT_j^2, and a theorem regarding the support of Dunkl translations  of L^2 compactly supported functions  (not necessarily radial). This kind of results turn out to be useful tools in studying harmonic analysis in Dunkl setting. We will discuss this kind of applications in the second part of the talk. We will discuss how our tools can be used to for studying singular integrals of convolution type or Littlewood-Paley square functions in the Dunkl setting.

This talk is based on the joint articles with J-Ph. Anker and J. Dziubanski.

13.07.2021

Malte Behr (Universität Oldenburg)

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Quasihomogeneous Blow-Ups and Pseudodifferential Calculus on SL(n,R)

We consider the quasihomogeneous blow-up of a submanifold Y in a surrounding manifold with corners X. It generalizes the concept of radial blow-up and revolves around the idea of assigning different weights to functions vanishing at the submanifold Y. In the second part, we consider the hd-compactification of SL(n,R), introduced by Albin, Dimakis, Melrose and Vogan. . We introduce a resolution of this compactification, on which right-invariant differential operators have simple degeneracies at the boundary. We construct an algebra of pseudodifferential operators on X. It is constructed using a resolution of X^2 by a series of quasihomogeneous blow-ups.                                                                                                      

20.07.2021

Jorge Vargas (Universidad Nacional de Córdoba)

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Restriction of square-integrable representations

Let $G$ be a semisimple Lie group, and $(\pi,V)$ a irreducible square integrable representation for $G$. Thus, a model for $V$ is the $L^2$-kernel of a elliptic operator  on a fiber bundle over the symmetric space $G/K$ attached to $G$. Let $H$ be a closed reductive subgroup for $G$. We say $\pi$ is $H$-discretely decomposable ( $H$-admissible) if the sum of the closed  $H$-irreducible subspaces in $V$ is dense in $V$, ($H$-admissible if it is $H$-discretely decomposable and the multiplicity of each irreducible factor is finite). We will give criteria for being $H$-$\cdots$ in language of spherical functions as well as in terms of structure of  intertwining operators. We will present   some aspects of branching problems and results in Orsted-Vargas, Branching problems in reproducing kernel spaces, Duke mathematical journal, Vol. 169, 3478-3537, 2020 and some  consequences.

27.10.2020

NN

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tba                                                                                                      

03.11.2020

Beatrice Pozzetti (Universität Heidelberg)

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Anosov representations are a robust and well studied class of discrete subgroups of non-compact simple Lie groups, which generalize many geometric features of hyperbolic manifolds to higher rank locally symmetric spaces. After a gentle introduction motivating the study of this class of groups, I will discuss joint work with Andres Sambarino and Anna Wienhard in which we establish a relation between a suitably chosen growth rate in the symmetric space and the Riemannian Hausdorff dimension of the minimal invariant subset in a flag manifold.                                                                                                    

10.11.2020

Clemens Weiske (Aarhus University)

Titel:

Symmetry breaking operators and unitary branching laws

Let $\pi$ be a unitary irreducible representation of a real reductive Lie group $G$. Naturally the restriction $\pi|_H$ to a reductive subgroup $H$ defines a unitary representation of $H$ and decomposes into a direct integral of unitary irreducible $H$-representations. We introduce a method to prove such a direct integral decomposition for unitary representations inside principal series representations, which expands classical Plancherel theorems for homogenous $H$-spaces to branching laws. This is done by an analytic continuation procedure in meromorphic parameters of certain $G$ and $H$-intertwining operators, namely symmetry breaking operators and Knapp--Stein operators. We will study examples where $G$ and $H$ are of real rank one.                                                                                                                                                                                                                                                                                                                                                                  

17.11.2020

Frederic Naud (Institut Mathematique Jussieu, Paris)

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We will introduce and review the notion of spectral gap related to the Laplace operator, both for compact and geometrically finite hyperbolic surfaces. We will then define a notion of random covers above a given hyperbolic surface and state some new results pertaining to the spectral gap in the large degree regime.                                                                                                                                                                                                                                                                           

24.11.2020

Stefan Hante (Universität Halle)

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Geometric time integration of a flexible Cosserat beam model

Cosserat beam models are used in industry as well as in academia to describe long and slender flexible structures like cables, hoses, rotor blades, etc. In my talk I will show how we can exploit the Lie group structure of the configuration space in order to discretize the beam model in space. Furthermore, I will introduce a numerical algorithm that can be used to approximately solve the remaining differential equation on a Lie group as well as touch on its numerical analysis. I will show computational tests as well as some industrial applications.                                                                                                                                                                                                                                                                     

01.12.2020

Nils Matthes (University of Oxford)

Titel:

Meromorphic modular forms and their iterated integrals

Meromorphic modular forms are generalizations of modular forms which are allowed to have poles. Part of the motivation for their study comes from recent work of Li–Neururer, Pasol–Zudilin, and others, which shows that integrals of certain meromorphic modular forms have integer Fourier coefficients – an arithmetic phenomenon which does not seem to exist for holomorphic modular forms. In this talk we will study iterated integrals of meromorphic modular forms and describe some general algebraic independence results, generalizing results of Pasol–Zudilin. If time permits we will also mention an algebraic geometric interpretation of meromorphic modular forms which generalizes the classical fact that modular forms are sections of a certain line bundles.                                                                                                                                                                                                                                                                                                                                                             

08.12.2020

Mihajlo Cekic (Universite Paris-Sud, Orsay)

Titel:

If a vector field X generates an Anosov flow, using the theory of anisotropic Sobolev spaces it is possible to define a discrete spectrum of X (as a differential operator), called Pollicott-Ruelle resonances. In this talk we show that if X additionally preserves a contact form (eg. X is the geodesic flow), this spectrum has structure, i.e. there exists a vertical band of resonances. In particular, it follows that the flow is exponentially mixing. Our proof uses semiclassical measures, slightly exotic pseudodifferential calculus and propagation estimates, and a careful analysis near the trapped set. Joint work with Colin Guillarmou.                                                                                                                                                                                                                                                                                                                                                                             

15.12.2020

Jan Frahm (Aarhus University)

Titel:

Conformally invariant differential operators on Heisenberg groups and minimal representations

On Euclidean space, the Fourier transform intertwines partial derivatives and coordinate multiplications. As a consequence, solutions to a constant coefficient PDE $p(D)u=0$ are mapped to distributions supported on the variety $\{p(x)=0\}$. In the context of unitary representation theory of semisimple Lie groups, so-called minimal representations are often realized on Hilbert spaces of solutions to systems of constant coefficient PDEs whose inner product is difficult to describe (the non-compact picture of a degenerate principal series). The Euclidean Fourier transform provides a new realization on a space of distributions supported on a variety where the invariant inner product is simply an $L^{^2}$-inner product on the variety. Recently, similar systems of differential operators have been constructed on Heisenberg groups. In this talk I will explain how to use the Heisenberg group Fourier transform to obtain a similar picture in this context.                                                                                                                                                                   

12.01.2021

Fabian Januszewski (Universität Paderborn)

Titel:

Tensor-structures in non-commutative harmonic analysis

Motivated by arithmetic questions, I will discuss approaches involving the symmetric monoidal structure of (g,K)-modules in the representation theory of real reductive groups.                                                                                                                                                                                                                                                                                  

19.01.2021

Paul Nelson (ETH Zürich)

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I will describe how the orbit method can be developed in a quantitative form, along the lines of microlocal analysis, and applied to local problems in representation theory and global problems concerning automorphic forms.  The local applications include asymptotic expansions of relative characters.  The global applications include moment estimates and subconvex bounds for L-functions.  These results are the subject of two papers, the first joint with Akshay Venkatesh:

https://arxiv.org/abs/1805.07750

https://arxiv.org/abs/2012.02187                                                                                                                                                                                                                       

26.01.2021

Jasmin Matz (University of Copenhagen)

Titel:

Quantum ergodicity of compact quotients of SL(n,R)/SO(n) in the level aspect

Suppose M is a closed Riemannian manifold with an orthonormal basis B of L²(M) consisting of Laplace eigenfunctions. Berry's Random Wave Conjecture tells us that under suitable conditions on M, in the high energy limit (ie, large Laplace eigenvalue) elements of B should roughly behave like random waves of corresponding wave number. A classical result of Shnirelman and others that M is quantum ergodic if the geodesic flow on the cotangent bundle of M is ergodic, can then be viewed as a special case of this conjecture. We now want to look at a level aspect, namely, instead of taking a fixed manifold and high energy eigenfunctions, we take a sequence of Benjamini-Schramm convergent compact Riemannian manifolds together with Laplace eigenfunctions f whose eigenvalue varies in short intervals. This perspective has been recently studied in the context of graphs by Anantharaman and Le Masson, and for hyperbolic surfaces and manifolds by Abert, Bergeron, Le Masson, and Sahlsten. In my talk I want to discuss joint work with F. Brumley in which we study this question in higher rank, namely sequences of compact quotients of SL(n,R)/SO(n), n>2.                                                                                                                                                                                                                                                                               

02.02.2021

Andreas Mono (Universität zu Köln)

Titel:

On small divisor functions and a construction of polar harmonic mass forms

Recently, Mertens, Ono, and Rolen studied mock modular analogues of Eisenstein series. Their coefficients are given by small divisor functions, and have shadows given by classical Shimura theta functions. Here, we construct a second class of small divisor functions, and prove that these generate the holomorphic part of polar harmonic (weak) Maaß forms of weight 3/2. Specializing to a certain choice of parameters, we obtain an identity between our small divisor function and Hurwitz class numbers. Lastly, we present p-adic congruences of our polar (weak) harmonic Maaß form, when p is an odd prime. This is joint work with Joshua Males and Larry
Rolen.                                                 

09.02.2021

Luz Roncal (BCAM- Basque Center for Applied Mathematics)

Titel:

Hardy's inequalities and an extension problem on $NA$ groups

We will introduce Hardy's inequality from several points of view and we will turn into its fractional version. One of the approaches to prove fractional Hardy's inequality leads to the study of solutions of the extension problem (that has received much attention in the last few years, especially among the PDE community). It happens that these solutions are related with the eigenfunctions of Laplace-Beltrami operators, which motivates the problem of characterising such eigenfunctions.

The aim of this talk is to provide an overview of the above topics and to report recent progress, putting an emphasis on the context of $NA$ groups.

Joint work with Sundaram Thangavelu (Indian Institute of Sciences in Bangalore, India).                                                           

N.N.

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Tobias Weich (Paderborn)

Titel:

Ruelle-Taylor Resonanzen für Anosov Wirkungen höheren Rangs

 In diesem Vortrag soll erklärt werden wie man mittels der Theorie des Taylor Spektrums kommutierender Operatoren sowie mikrolokaler Analysis einer Anosov Wirkung höheren Rangs ein intrinsisches diskretes Resonanzsspektrum zuordnen kann.                                                                                                         

Lasse Wolf (Paderborn)

Quantum-Classical correspondance in higher rank

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Beatrice Pozzetti (Heidelberg)                                  

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canceled due to Corona restrictions                                                                                                                               

Margit Rösler (Paderborn)

Riesz-Distributionen im Dunkl-Setting vom Typ A

Nach einem klassischen Resultat von Gindikin ist eine Riesz-Distribution auf einem symmetrischen Kegel genau dann ein positivies Maß, wenn ihr Index zur Wallachmenge gehört. Gegenstand dieses Vortrags ist ein Analogon dieser Aussage im Rahmen der rationalen Dunkl-Theorie zu Wurzelsystemen vom Typ A. Die verallgemeinerte Wallachmenge ist dabei durch die Multiplizität der Dunkl-Operatoren parametrisiert. Wir erläutern auch die Rolle dieser verallgemeinerten Wallachmenge im Zusammenhang mit der Existenz positiver Vertauschungsoperatoren.

Kai-Uwe Bux (Bielefeld)

Coarse Topological Group Invariants

It is hopeless to classify infinite groups up to isomorphism. There are several invariants one can use to chart the vast area inhabited by such groups. I shall discuss several numerical group invariants coming from topology, homology, and geometry: *

• finiteness properties 

• (co)homologicial and geometric dimensions 

• isoperimetric inequalities

I shall illustrate these concepts (with a focus on finiteness properites). Groups of matrices provide a good source of examples.                                                                                                                              

Jungwon Lee (Sorbonne Université)

Dynamics of continued fractions and conjecture of Mazur-Rubin

Mazur and Rubin established several conjectural statistics for modular symbols. We show that the conjecture holds on average. We plan to introduce the approach based on spectral analysis of transfer operator associated to a certain skew-product Gauss map and consequent result on mod p non-vanishing of modular L-values with Dirichlet twists (joint with Hae-Sang Sun).
                                                                                                                               

Thomas Mettler (Frankfurt)

Lagrangian minimal surfaces, hyperbolicity and dynamics

The Beltrami—Klein model leads to a natural generalisation of hyperbolic surfaces in terms of so-called properly convex projective surfaces. In my talk I will relate these properly convex projective surfaces to certain Lagrangian minimal surfaces. This gives rise to a new class of dynamical systems and I will discuss some of their properties. In parts, this talk is based on joint work with Maciej Dunajski and Gabriel Paternain.                                                                                                                                  

Gabriel Rivière (Nantes)

Poincaré series and linking of Legendrian knots

 Given two points on a compact Riemannian surface with variable negative curvature, one can consider the lengths of all the geodesic arcs joining these two points and form a natural zeta function associated with these lengths (the so-called Poincaré series). I will explain that this Poincaré series has a meromorphic continuation to the whole complex plane. Then, I will show that the value at 0 is given by the inverse of the Euler characteristic by interpreting this value at 0 as the linking of two Legendrian knots. If time permits, I will explain how the results can be extended when one consider the geodesic arcs orthogonal to two closed geodesics. (joint work with Nguyen Viet Dang)                                                                                                    

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Sven Möller (Rutgers University)

Dimension Formulae and Generalised Deep Holes of the Leech
Lattice Vertex Operator Algebra

Conway, Parker and Sloane (and Borcherds) showed that there is a natural bijection between the Niemeier lattices (the 24 positive-definite, even, unimodular lattices of rank 24) and the deep holes of the Leech lattice, the unique Niemeier lattice without roots.

We generalise this statement to vertex operator algebras (VOAs), i.e. we show that all 71 holomorphic VOAs (or meromorphic 2-dimensional conformal field theories) of central charge 24 correspond to generalised deep holes of the Leech lattice VOA.

The notion of generalised deep hole occurs naturally as an upper bound in a dimension formula we obtain by pairing the character of the VOA with a certain vector-valued Eisenstein series of weight 2.

(This is joint work with Nils Scheithauer.)                                                                                                                                  

Michael Voit (TU Dortmund)

Limit theorems for Calogero-Moser-Sutherland particle models in the freezing regime

Calogero-Moser-Sutherland models are described by some root system and some coupling constants. They are closely related with several random matrix models and, for some cases, with Brownian motions on Grassmann manifolds.
In this talk we discuss some limit results when the the coupling constants tend to infinity. Here the limits can be described  in terms of deterministic limit dynamical systems and zeroes of classical orthogonal polynomials. We also present some results when the number of particles tends to infinity.                                                                                                                         

Lennart Gehrmann (Essen)

Big principal series and L-invariants

By a result of Bertolini, Darmon and Iovita the Orton L-invariant of a modular form equals the derivative of the U_p-eigenvalue of a p-adic family passing through it. In this talk I will give a new, more conceptual proof of the result. One advatange of the method is that it can be generalized to automorphic forms on higher rank groups. This is joint work with Giovanni Rosso.                                                                                                                            

Elmar Schrohe (Hannover)

Abstract (as pdf file)

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Nguyen Thi Dang (Universität Heidelberg)

Topological mixing of the Weyl chamber flow

Let G be a semisimple Lie group without compact factors. Consider A a maximal split torus and a maximal compact subgroup K for which the Cartan decomposition holds. Denote by M the centralizer subgroup of A in K . Let Γ be a discrete subgroup of G, acting properly discontinuously on G/K . In the case of G = PSL(2, R), the right action of A on Γ\G identies with the action of the geodesic ow on the unit tangent bundle of Γ\H2 . The latter has been well studied and satises many chaotic properties such as topological mixing in its non-wandering set. My talk addresses the case when A is of higher dimension and Γ is not a lattice. First I will introduce the main topological property: topological mixing. Then I will state a joint result with Olivier Glorieux, a necessary and sucient condition for topological mixing of actions of one parameter subgroups φt of A on Γ\G/M . Then I will introduce a few key tools: the Benoist limit cone and Hopf coordinates of G/M . Finally, I will give the main ideas behind the proof of the topological mixing Theorem. Time permitting, I will present a generalization of this Theorem for the right action of φt on Γ\G when M is abelian and connected.                                                                                                                     

Maxime Ingremeau (Université de Nice Sophia-Antipolis)

Titel:

Around Berry’s random waves conjecture

40 years ago, the physicist Michael Berry suggested that eigenfunctions of the Laplacian on manifolds of negative curvature should be well described, in the high-frequency limit, by some random function, given by an isotropic monochromatic Gaussian field. After recalling various mathematical interpretations of this conjecture, we will discuss how Bourgain’s arithmetic « derandomization technique » allow to prove the conjecture for eigenfunctions on the two-dimensional torus. We will show that the conjecture holds in a weak form for some families of quasi-modes, namely, long-time evaluated Lagrangian distributions on manifolds of negative curvature.                                                                                                                   

Lasse Wolf (Universität Paderborn)

Spectral Asymptotics for kinetic Brownian Motion on hyperbolic surfaces

The kinetic Brownian motion on the sphere bundle of a Riemannian manifold M is a stochastic process that models a random perturbation of the geodesic flow. If M is a orientable compact constant negatively curved surface, we show that in the limit of infinitely large perturbation the L2-spectrum of the infinitesimal generator of a time rescaled version of the process converges to the Laplace spectrum of the base manifold. In addition, we give explicit error estimates for the convergence to equilibrium. The proofs are based on noncommutative harmonic analysis of SL2(R).                                                                                                                              

Dieser Vortrag ist der erste in einer Serie von zwei Vorträgen über spezielle Werte von L-Funktionen. In diesem ersten Vortrag über Rationalität von L-Werten wird auf die konzeptionelle Motivation und Resultate eingegangen. Im Kontext letzterer spielen (g,K)-Moduln eine wichtige Rolle.                                                                                                                                    

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To each non-zero discriminant D one can associate a modular form f_k,D of weight 2k, which is a cusp form if D > 0 and a meromorphic modular form if D < 0. It is well known that the two-variable generating series obtained by summing up the cusp forms f_k,D with D > 0 is modular in both variables. It yields the Kohnen-Zagier kernel function for the Shimura correspondence. Furthermore, the generating series of traces of geodesic cycle integrals of f_k,D for fixed D > 0 is a cusp form of half-integral weight 1/2+k. In this talk we explain how the two-variable generating series of the meromorphic modular forms f_k,D for D < 0 as well as the generating series of traces of cycle integrals of f_k,D for fixed D < 0 can be completed to real-analytic modular forms. Furthermore, we explain some rationality results for the traces of cycle integrals of the meromorphic modular forms f_k,D for D < 0.                                                                                                        

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One purpose of modular forms, and more generally, weakly holomorphic
modular forms is to aid or even enable the analysis of certain
generating series, namely modular generating series. A common question
asked for coefficients $c(n)$ of a generating series is which patterns
of divisibility they satisfy. Among the most accessible patterns, there
is divisibility on arithmetic progressions: $c(an + b)$ is divisible by
a given positive integer $\ell$ for all $n$. The theory of modular forms
modulo primes yields a good handle on such question as long as $a$ and
$b$ are remain fixed and $\ell$ is prime.

In this talk, we showcase a new technique that allows us to answer in
the affirmative the question of whether there is a connection among
congruences for varying $b$ and fixed $a$. As a result, we discover
surprisingly strong restrictions on maximal arithmetic progressions that
admit a congruence. We primarily build upon results by Deligne-Rapoport
on the arithmetic compactification of the moduli of elliptic curves. We
reduce the original problem to a very concrete one in the modular
representation theory of finite groups of Lie type and their covers,
which in our motivating setting can be solved by a calculation.                                                                                                                              

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In this talk we give an introduction to theta series and theta lifts and its representation-theoretic background. We then explain singular theta lifts of Borcherds type and employ the reductive dual pair U(p, q) × U(1, 1) to construct two different kinds of Green forms for codimension q-cycles in Shimura varieties associated to unitary groups. In particular, we establish an adjointness result between the singular theta lift and the Kudla-Millson theta lift and discuss further applications in the context of the Kudla Program.

This is joint work with Eric Hofmann.

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Claudia Alfes-Neumann -- Universität Paderborn

In this talk we review results of Bringmann and Kudla on the classification of harmonic Maass forms. In their paper they gave a classification of the Harish-Chandra modules generated by the pullback (to SL_2(R)) of harmonic weak Maass forms for congruence subgroups of SL_2(Z).

ACHTUNG:  Gemeinsames Oberseminar mit AG Algebra Vortrag findet in  D1 320 statt und startet schon um 14h.

Jan Frahm (geb Möllers) -- Universität Erlangen-Nürnberg

Titel:

Periodenintegrale, L-Funktionen und Multiplizität Eins

Einer automorphen Form auf der oberen Halbebene kann man durch Ihre Fourierkoeffizienten eine L-Funktion zuordnen. Allgemeiner kann man zwei automorphen Formen auf der oberen Halbebene die sogenannte Rankin-Selberg L-Funktion zuordnen, die durch Faltung der Fourierkoeffizienten gegeben ist. Diese Konstruktion lässt sich auf Paare automorpher Formen auf GL(m) und GL(n) verallgemeinern und hängt eng zusammen mit der Restriktion automorpher Formen von  GL(m) auf GL(n) (m\geq n) und Periodenintegralen. Im Vortrag wird dieser Zusammenhang erklärt und die Beziehung zur Restriktion (unendlich-dimensionaler) Darstellungen von GL(m) auf GL(n) hergestellt. Dadurch wird es möglich Abschätzungen für Rankin-Selberg L-Funktionen mit darstellungstheoretischen Methoden zu erreichen, insbesondere mit der Multiplizität Eins Eigenschaft.

Polyxeni Spilioti -- Universität Tübingen

Dynamical zeta functions, trace formulae
and applications

The dynamical zeta functions of Ruelle and Selberg are functions of a complex variable s and are associated with the geodesic flow on the unit sphere bundle of a compact hyperbolic manifold. Their representation  by Euler-type products traces back  to the Riemann zeta function. In this talk, we will present  trace formulae and Lefschetz formulae, and the machinery that they provide to study the analytic properties of the dynamical zeta functions and their relation to spectral invariants. In addition, we will present other applications of the Lefschetz formula, such as the prime geodesic theorem for locally symmetric spaces of higher rank.                                                                                                                                 

Feiertag

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Valentin Blomer -- Universität Göttingen

Mit der Poissonschen Summationsformel als Ausgangspunkt werden spektrale Summationsformeln auf lokal-symmetrischen Räumen vorgestellt zusammen mit einer Reihe arithmetischer und analytischer Anwendungen.

Anna von Pippich -- TU Darmstadt

The special value Z'(1) of the Selberg zeta function

In this talk, we report on an explicit formula for the special value at s=1 of the derivative of the Selberg zeta function for the modular group Gamma=PSL_2 (Z). The formula is a consequence of a generalization of the arithmetic Riemann--Roch theorem of Deligne and Gillet-Soule to the case of the trivial sheaf on Gamma\H, equipped with the hyperbolic metric.

The proof uses methods of zeta regularisation and relies on Mayer-Vietoris type formulas  for determinants of Laplacian. This is joint work with Gerard Freixas.

Achtung: Der Vortrag findet von 12:30-14h im Raum N 3.211 statt.

Michael Baake -- Universität Bielefeld

The plan of this talk is to recall some properties around
the diffraction and dynamical spectra of cut and project
and inflation point sets, with some emphasis on cases with
mixed spectrum and some examples of number-theoretic origin.
                                                                                                                               

Anna Wienhard -- Universität Heidelberg

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In asymptotic group theory, zeta functions have become important tools to study the asymptotic and finer arithmetic properties of the distribution of finitary invariants of infinite groups. Defined as Dirichlet generating series, they encode, for instance, the numbers of finite-index subgroups or finite-dimensionsional representations of a given infinite group.

Zeta functions associated to arithmetic groups often enjoy Euler products, indexed by the (Archimedean and non-Archimedean) places of number fields. The non-Archimedean factors tend to be rational functions. To understand how these functions vary with the place is among the fundamental challenging questions in the field.

I will report on recent work with Angela Carnevale and Michael Schein: we prove a conjecture of Grunewald, Segal, and Smith on the variation of local normal subgroup zeta functions of finitely generated free class-2-nilpotent groups under base extension with number rings. Our result establishes that, in this setup, the variation is "uniform on primes of fixed decomposition type" in the relevant number field.

ACHTUNG:  Es finden an diesem Tag aufgrund der Lesewoche zwei Vorträge 11:00-12:30 (in J 2.213) und 14:00-15:30 (E 2.304) statt.                                                                         

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Fällt aus wegen

PBMath Sommerschule