Harmonic Analysis Seminar
Abstract and additional information

Posted September 2, 2003

12:40 pm - 1:30 pm Lockett 381
Gestur Olafsson, Mathematics Department, LSU

Square Integrable Representations and Frames

Harmonic Analysis Seminar
Abstract and additional information

Posted September 5, 2003

Last modified September 8, 2003

Gestur Olafsson, Mathematics Department, LSU

Square Integrable Representations and Frames II

Harmonic Analysis Seminar
Abstract and additional information

Posted September 8, 2003

12:40 pm - 1:30 pm Lockett 381
Gestur Olafsson, Mathematics Department, LSU

Square Integrable Representations and Frames III

Harmonic Analysis Seminar
Abstract and additional information

Posted September 18, 2003

Last modified January 27, 2004

Karl Heinrich Hofmann, Darmstadt University, Germany
Professor Emeritus

How did the adjoint functor theorem get into Lie theory?

Visit supported by Visiting Experts Program in Mathematics, Louisiana Board of Regents. LEQSF(2002-04)-ENH-TR-13

Harmonic Analysis Seminar
Abstract and additional information

Posted October 6, 2003

12:40 pm - 1:30 pm Lockett 381
Shijun Zheng, LSU

The Perturbation of the Fourier Transform and Schroedinger Operators (continued)

Harmonic Analysis Seminar
Abstract and additional information

Posted October 17, 2003

12:40 pm - 1:30 pm Lockett 381
Shijun Zheng, LSU

The wavelet decomposition for operator multiplication

Harmonic Analysis Seminar
Abstract and additional information

Posted October 24, 2003

12:40 pm - 1:30 pm Lockett 381
Yongdo Lim, Kyungpook National University

Best Approximation in Riemannian Geodesic submanifolds of Positive Definite Matrices

Harmonic Analysis Seminar
Abstract and additional information

Posted October 30, 2003

12:40 pm - 1:30 pm Lockett 381
Mark Davidson, Mathematics Department, LSU

Generating Functions and Representation Theory

Harmonic Analysis Seminar
Abstract and additional information

Posted November 7, 2003

12:40 pm - 1:30 pm
Mark Davidson, Mathematics Department, LSU

Generating Functions and Representation Theory

Harmonic Analysis Seminar
Abstract and additional information

Posted January 27, 2004

3:00 am - 3:50 am Lockett 381
Jimmie Lawson, Mathematics Department, LSU

The symplectic group, the symplectic semigroup, and the Ricatti Equation

Harmonic Analysis Seminar
Abstract and additional information

Posted January 27, 2004

3:00 am - 3:50 am Monday, February 2, 2004 Lockett 381
Jimmie Lawson, Mathematics Department, LSU

The symplectic group, the symplectic semigroup, and the Ricatti Equation II

Harmonic Analysis Seminar
Abstract and additional information

Posted February 12, 2004

3:00 pm - 5:50 am Lockett 381
Jimmie Lawson, Mathematics Department, LSU

The symplectic group, the symplectic semigroup, and the Ricatti Equation III

Harmonic Analysis Seminar
Abstract and additional information

Posted March 7, 2004

3:00 pm - 3:50 am Lockett 381
Gestur Olafsson, Mathematics Department, LSU

The Fuglede conjecture and related problems.

Harmonic Analysis Seminar
Abstract and additional information

Posted March 8, 2004

3:03 pm - 3:52 pm Lockett 381
Simon Gindikin, Rutgers University

Some explicit formulas in integral geometry

Harmonic Analysis Seminar
Abstract and additional information

Posted March 15, 2004

3:00 pm - 3:50 pm Lockett 381
Karl Heinrich Hofmann, Darmstadt University, Germany
Professor Emeritus

Commuting exponential matrices and Lie theory

Harmonic Analysis Seminar
Abstract and additional information

Posted April 1, 2004

3:00 pm - 3:50 pm Lockett 381
Shijun Zheng, LSU

Operator representation in wavelet bases and Application in PDE's. Part 2.

Abstract. We give a short review on recent development on wavelet-based numerical solution of time-dependent partial differential equations. The fundamental idea is to use wavelet to give sparse matrix representations of the solution operators involved. Thus it leads to a fast algorithm for efficient approximation of the solution to the equation. We demonstrate the general scheme by considering the anisotropic diffusion problem arising in modeling thin film image processing. Other examples are advection-diffusion equations in $CFD$, including the connection with the incompressible Navier-Stokes equations in semigroup formulation.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 20, 2004

3:00 pm - 3:50 pm Lockett 381
Boris Rubin, Louisiana State University

Zeta integrals and Radon transforms on the space of rectangular matrices

Harmonic Analysis Seminar
Abstract and additional information

Posted April 20, 2004

2:30 pm - 3:30 pm Lockett 381
Ziemowit Rzeszotnik, University of Texas, Austin

Norm of the Fourier transform on finite abelian groups

Harmonic Analysis Seminar
Abstract and additional information

Posted April 27, 2004

3:00 pm - 3:50 pm Lockett 381
Dave Larson, Texas A&M

Wavelet sets and Frames

Harmonic Analysis Seminar
Abstract and additional information

Posted September 9, 2004

2:40 pm - 3:30 pm Lockett 381
Jens Christensen, Mathematics Department, LSU

Uncertainty principles generated by Lie-groups

Harmonic Analysis Seminar
Abstract and additional information

Posted September 17, 2004

2:40 pm - 3:30 pm Lockett 381
Jens Christensen, Mathematics Department, LSU

Uncertainty principles generated by Lie-groups

Harmonic Analysis Seminar
Abstract and additional information

Posted September 22, 2004

2:40 pm - 3:30 pm Lockett 381
Jens Christensen, Mathematics Department, LSU

An Uncertainty Principle Related to the Euclidean motion group

I will show that a well known uncertainty principle for functions on the circle can be derived from the generators of the Euclidean motion group.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 30, 2004

2:40 pm - 3:30 pm Lockett 381
Daniel Sage, Mathematics Department, LSU

Group and Hopf algebra actions on central simple algebras.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 18, 2004

2:40 pm - 3:30 pm Lockett 312
Daniel Sage, Mathematics Department, LSU

Group and Hopf algebra actions on central simple algebras. II

Harmonic Analysis Seminar
Abstract and additional information

Posted October 22, 2004

2:40 pm - 3:30 pm Lockett 281
Daniel Sage, Mathematics Department, LSU

Group and Hopf algebra actions on central simple algebras. III

Harmonic Analysis Seminar
Abstract and additional information

Posted November 3, 2004

2:40 pm - 3:30 pm Lockett 381
Daniel Sage, Mathematics Department, LSU

Group and Hopf algebra actions on central simple algebras. IV

Harmonic Analysis Seminar
Abstract and additional information

Posted November 3, 2004

2:40 pm - 3:30 pm Lockett 381
Daniel Sage, Mathematics Department, LSU

Group and Hopf algebra actions on central simple algebras. V

Harmonic Analysis Seminar
Abstract and additional information

Posted January 25, 2005

10:40 am - 11:30 am Lockett 282
Jimmie Lawson, Mathematics Department, LSU

Symmetric Spaces with Seminegative Curvature

Harmonic Analysis Seminar
Abstract and additional information

Posted January 25, 2005

10:40 am - 11:30 am Lockett 282
Jimmie Lawson, Mathematics Department, LSU

Symmetric Spaces of Seminegative Curvature

Harmonic Analysis Seminar
Abstract and additional information

Posted February 4, 2005

10:40 am - 11:30 am Lockett 282
Jimmie Lawson, Mathematics Department, LSU

Symmetric Spaces of seminegative curvature

Harmonic Analysis Seminar
Abstract and additional information

Posted February 16, 2005

10:40 am - 11:30 am Lockett 282
Leticia Barchini, Oklahoma State University at Stillwater

Remarks on the characteristic cycle of discrete series of SU(p,q)

Harmonic Analysis Seminar
Abstract and additional information

Posted February 22, 2005

10:40 am - 11:30 am Lockett 282
Boris Rubin, Louisiana State University

The Composite Cosine Transform on the Stiefel Manifold

Harmonic Analysis Seminar
Abstract and additional information

Posted March 3, 2005

10:40 am - 11:30 am Lockett 282
Boris Rubin, Louisiana State University

The Composite Cosine Transform on the Stiefel Manifold II

Harmonic Analysis Seminar
Abstract and additional information

Posted March 31, 2005

10:40 am - 11:30 am Lockett 282
Daniel Sage, Mathematics Department, LSU

Racah Coefficients and Subrepresentation Semirings

Harmonic Analysis Seminar
Abstract and additional information

Posted April 11, 2005

10:40 am - 11:30 am Lockett 282
Daniel Sage, Mathematics Department, LSU

Racah Coefficients and Subrepresentation semigroups. II

Harmonic Analysis Seminar
Abstract and additional information

Posted April 19, 2005

10:40 am - 11:30 am Lockett 282
Daniel Sage, Mathematics Department, LSU

Racah Coefficients and Subrepresentation Semirings III

Harmonic Analysis Seminar
Abstract and additional information

Posted April 20, 2005

10:40 am - 11:30 am Lockett 282
Gestur Olafsson, Mathematics Department, LSU

The Image of the Heat Transform on Symmetric Spaces

Harmonic Analysis Seminar
Abstract and additional information

Posted September 8, 2005

2:40 pm - 3:30 pm Lockett 381
Mark Davidson, Mathematics Department, LSU

Differential Recursion Relations for Laguerre Functions on Symmetric Cones

Harmonic Analysis Seminar
Abstract and additional information

Posted September 18, 2005

2:40 pm - 3:30 pm Lockett 381
Mark Davidson, Mathematics Department, LSU

Differential Recursion Relations for Laguerre Functions on Symmetric Cones II

Harmonic Analysis Seminar
Abstract and additional information

Posted September 21, 2005

2:40 pm - 3:30 pm Lockett 381
Gestur Olafsson, Mathematics Department, LSU

The Image of the Segal-Bargman Transform

Harmonic Analysis Seminar
Abstract and additional information

Posted September 28, 2005

2:40 pm - 3:30 pm Lockett 381
Gestur Olafsson, Mathematics Department, LSU

The Image of the Segal-Bargman Transform II

Harmonic Analysis Seminar
Abstract and additional information

Posted October 7, 2005

2:40 am - 3:30 am Lockett 381
Gestur Olafsson, Mathematics Department, LSU

The Image of the Segal-Bargman Transform III

Harmonic Analysis Seminar
Abstract and additional information

Posted October 13, 2005

Last modified October 14, 2005

Hongyu He, Mathematics Department, LSU

Some problems concerning positive definite functions

I will give an introduction about positive definitive function and its relation to unitary representation theory, Bochner's Theorem, Gelfand-Naimark-Segal construction etc. Then I will define positive definite distributions and introduce the extension problems, square root problems and the positivity roblem of Godement. This talk will be accessible to graduate students.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 20, 2005

2:40 pm - 1:30 pm Lockett 381
Boris Rubin, Louisiana State University

The generalized Busemann-Petty problem on sections of convex bodies.

The generalized Busemann-Petty problem asks whether origin-symmetric convex bodies in $R^n$ with smaller $i$-dimensional central sections necessarily have smaller volume. This problem has a long history. For $i=2$ and $3$, the answer is still unknown if $n>4$. The problem is intimately connected with the spherical Radon transform. I am planning to give a survey of known results and methods, discuss some generalizations and difficulties.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 27, 2005

Last modified October 28, 2005

Boris Rubin, Louisiana State University

The generalized Busemann-Petty problem on sections of convex bodies.II

The generalized Busemann-Petty problem asks whether origin-symmetric convex bodies in $R^n$ with smaller $i$-dimensional central sections necessarily have smaller volume. This problem has a long history. For $i=2$ and $3$, the answer is still unknown if $n>4$. The problem is intimately connected with the spherical Radon transform. I am planning to give a survey of known results and methods, discuss some generalizations and difficulties.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 28, 2005

2:40 pm - 3:30 pm 338 Johnston Hall
Eric Todd Quinto, Mathematics Department, Tufts University

LIMITED DATA TOMOGRAPHY AND MICROLOCAL ANALYSIS

In this talk, we will describe limited data tomography problems that come up in applications, including electron microscopy and diagnostic radiology. In each of these tomography problems, certain singularities (boundaries, cracks, etc.) of the object are easily visible in the reconstruction and others are not. We will show how this phenomenon is reflected in the singular functions for the corresponding tomographic problems. A theoretical framework, microlocal analysis, will be given to explain the phenomenon, and we will include an elementary introduction to this idea. If time, we will outline our basic algorithm.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 28, 2005

2:40 pm - 3:30 pm 381 Lockett Hall
Ricardo Estrada, Mathematics Department, LSU

Average local behavior of functions and Fourier Series

Harmonic Analysis Seminar
Abstract and additional information

Posted January 24, 2006

3:40 pm - 4:30 pm Lockett 381
Gestur Olafsson, Mathematics Department, LSU

Determining Intertwining Operators

Harmonic Analysis Seminar
Abstract and additional information

Posted February 8, 2006

3:40 pm - 4:30 pm Lockett 381
Gestur Olafsson, Mathematics Department, LSU

Determining Intertwining Operators II

Harmonic Analysis Seminar
Abstract and additional information

Posted February 2, 2006

Last modified February 22, 2006

See program announcement

Workshop in Harmonic Analysis and Fractal Geometry

http://www.math.lsu.edu/~olafsson/workshop06.html

Harmonic Analysis Seminar
Abstract and additional information

Posted March 14, 2006

3:40 pm - 4:30 pm Lockett 381
Gestur Olafsson, Mathematics Department, LSU

Determining Intertwining Operators III

Harmonic Analysis Seminar
Abstract and additional information

Posted March 24, 2006

3:40 pm - 4:30 pm Lockett 381
Boris Rubin, Louisiana State University

On MATH 7390-1: Applied Harmonic Analysis (Fall 2006)

Abstract. I am planning to review a tentative content of this course which will be suggested to graduate students in Fall 2006. This is an introductory course in the theory of the Radon transform, one of the main objects in integral geometry and modern analysis. Topics to be studied include fractional integration and differentiation of functions of one and several variables, Radon transforms in the n-dimensional Euclidean space and on the unit sphere, selected aspects of the Fourier analysis in the context of its application to integral geometry and tomography. The talk will be illustrated by examples of mathematical problems that fall into the scope of this course.

Harmonic Analysis Seminar
Abstract and additional information

Posted March 28, 2006

3:40 pm - 4:30 pm Lockett 381
Genkai Zhang, Department of Mathematics, Gothenburg University, Sweden

Radon, cosine and sine transforms on Grassmannians.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 25, 2006

2:40 pm - 3:30 pm Lockett 381
Tomasz Przebinda, University of Oklahoma

Orbital Integrals and Howe's Correspondence

Abstract. In this talk I shall explain the construction of the invariant eigendistributions in more detail. In particular, we’ll show how it relates Harish-Chandra’s orbital on the Lie algebras via and the moment maps.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 11, 2006

3:40 pm - 4:30 pm Lockett 381
Hongyu He, Department of Mathematics, LSU

Complementary series of the Universal Covering of the Symplectic Group

Abstract: Complementary series arise as pertubation of the (degenerate) principal series. I will first discuss Sahi's classification. I will then show that complementary series restricted to a symplectic subgroup "half" of its original size are unitarily equivalent to the corresponding restriction of the principal series. The equivalence is given by the "square" root of the intertwining operator expressed in terms of the mixed model, which I will define. This talk is closely related to G. Olafsson's talk last semester in which he discussed the intertwining operator expressed in terms of the compact model.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 14, 2006

3:40 pm - 4:30 pm Lockett 381
Hongyu He, Mathematics Department, LSU

Complementary series of the Universal Covering of the Symplectic Group II

Abstract: Complementary series arise as pertubation of the (degenerate) principal series. I will first discuss Sahi's classification. I will then show that complementary series restricted to a symplectic subgroup "half" of its original size are unitarily equivalent to the corresponding restriction of the principal series. The equivalence is given by the "square" root of the intertwining operator expressed in terms of the mixed model, which I will define. This talk is closely related to G. Olafsson's talk last semester in which he discussed the intertwining operator expressed in terms of the compact model.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 10, 2006

3:40 pm - 4:30 pm Lockett 381
Andy Sinton, Hebrew University of Jerusalem

Direct and Inverse Limits in Geometry and Representation Theory

Abstract: Direct limits (i.e. unions) of finite-dimensional groups are a natural place to look for infinite-dimensional generalizations of the finite-dimensional representation theory and related geometry. In many situations, it turns out that the appropriate analog for the regular representation is a found by letting the direct limit group act on the inverse limit of a related (quotient) space. The first half of the talk will provide an overview of the results of Olshanski, Vershik, Borodin, and others in the cases of the symmetric group and compact symmetric spaces. In the second half I will discuss the state of the art for non-compact symmetric spaces, which I am working on with Gestur Olafsson. Only a basic background in representation theory and Lie groups will be assumed.

Harmonic Analysis Seminar
Abstract and additional information

Posted November 6, 2006

3:40 pm - 4:30 pm Lockett 381
Jens Christensen, Mathematics Department, LSU

Time-Frequency analysis and Gelfand triples

In the 80's Feichtinger and Groechenig found a general class of Banach spaces tied to integrable group representations. These are called coorbit spaces and they are spaces for which the representation coefficients give isometric isomorphisms into other Banach spaces (for example weighted L_p spaces). A well known example is the class of modulation spaces, but also Besov spaces are coorbit spaces (this is rather loosely claimed by Feichtinger and Groechenig). I try to generalize the concept of coorbit spaces to make this construction easier and also possible for non-integrable square integrable representations. This work has been carried out together with Prof. Olafsson.

Harmonic Analysis Seminar
Abstract and additional information

Posted November 13, 2006

Last modified November 27, 2006

Suat Namli, Louisiana State University
Graduate Student

A white noise analysis idea applied to orthogonal polynomials

Harmonic Analysis Seminar
Abstract and additional information

Posted February 28, 2007

3:40 pm - 4:30 pm Lockett 381
Michael Otto, University of Arizona

Poisson geometry and symmetric spaces

Abstract: Methods from Poisson/symplectic geometry can be used to study properties of Lie groups and associated symmetric spaces. A prominent example is provided by the classical symplectic convexity theorem of Atiyah and Guillemin-Sternberg and its connection with Kostant's convexity theorem for semisimple Lie groups. We will introduce several interesting Poisson structures on a symmetric space and discuss applications.

Harmonic Analysis Seminar
Abstract and additional information

Posted March 14, 2007

Last modified March 15, 2007

Hongyu He, Mathematics Department, LSU

Introduction to Theta Correspondence

In this talk, I will introduce Howe's dual reductive pair. I will then discuss

the basic theory of theta correspondence and its application in representation

theory. The talk will be accessible to graduate students.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 10, 2007

3:40 pm - 4:30 pm Lockett 285
Hongyu He, Mathematics Department, LSU

Introduction to Theta Correspondence II

In this talk, I will introduce Howe's dual reductive pair. I will then discuss the basic theory of theta correspondence and its application in representation theory. The talk will be accessible to graduate students.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 24, 2007

3:40 pm - 4:30 pm Lockett 381
Hongyu He, Department of Mathematics, LSU

Introduction to Theta Correspondence III

In this talk, I will introduce Howe's dual reductive pair. I will then discuss the basic theory of theta correspondence and its application in representation theory. The talk will be accessible to graduate students.

Harmonic Analysis Seminar
Abstract and additional information

Posted May 4, 2007

3:40 pm - 4:30 pm Lockett 381
Raul Quiroga, Centro de Investigacion en Matematicas (cimat)

Rigidity results for pseudoRiemannian manifolds

Abstract: We will continue our discussion of compact pseudoRiemannian manifolds with a noncompact simple Lie group of isometries. It will be seen that such pseudoRiemannian manifolds have two very remarkable properties: 1) they carry large local isotropy groups, 2) they are locally homogeneous on an open dense subset. These will allow us to describe some structure results for the pseudoRiemannian manifolds considered. As a consequence, we will prove that if $M$ is an irreducible pseudoRiemannian manifold with an isometric action of $SO(p,q)$ and $dim(M) \leq dim(SO(p,q)) + p + q$, then the universal covering space of $M$ is a noncompact simple Lie group.

Harmonic Analysis Seminar
Abstract and additional information

Posted May 3, 2007

3:40 pm - 4:30 pm Lockett 381
Hongyu He, Department of Mathematics, LSU

Introduction to Theta Correspondence IV

Harmonic Analysis Seminar
Abstract and additional information

Posted September 28, 2007

3:40 pm - 4:30 pm Lockett 381
Jens Christensen, Mathematics Department, LSU

Bergman spaces and representations of SL_2

Graduate Students are encouraged to attend. Abstract: I will start by presenting a general framework for describing Banach spaces by use of representations. Next I will take a closer look at a specific representation leading to a characterization of Bergman spaces on the unit disc. The talk will most likely be split on two days.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 28, 2007

3:40 pm - 3:30 pm Lockett 381
Jens Christensen, Mathematics Department, LSU

Bergman spaces and representations of SL_2 II

Graduate Students are encouraged to attend. Abstract: I will start by presenting a general framework for describing Banach spaces by use of representations. Next I will take a closer look at a specific representation leading to a characterization of Bergman spaces on the unit disc. The talk will most likely be split on two days.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 17, 2007

3:40 pm - 4:30 pm Lockett 381
Jens Christensen, Mathematics Department, LSU

Bergman spaces and representations of SL_2 III

Graduate Students are encouraged to attend. Abstract: I will start by presenting a general framework for describing Banach spaces by use of representations. Next I will take a closer look at a specific representation leading to a characterization of Bergman spaces on the unit disc. The talk will most likely be split on two days.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 19, 2007

Last modified September 24, 2007

Alex Iosevich , University of Missouri-Columbia

Bounds for discrete Radon transforms and application to problems in geometric combinatorics and additve number theory

Harmonic Analysis Seminar
Abstract and additional information

Posted October 5, 2007

3:40 pm - 4:30 pm Lockett 381
Martin Laubinger, LSU
Graduate Student

Complex Structures on Principal Bundles

Holomorphic principal G-bundles over a complex manifold M can be studied using non-abelian cohomology groups H1(M,G). On the other hand, if M=\Sigma is a closed Riemann surface, there is a correspondence between holomorphic principal G-bundles over \Sigma and coadjoint orbits in the dual of a central extension of the Lie algebra C^\infty(\Sigma, \g). We review some of these results and use a Theorem of A. Borel to give more detail in the case of \Sigma having genus one. The talk is based on my diplom thesis, a short version of which is available on the ArXiv: arXiv:0708.3261v1

Harmonic Analysis Seminar
Abstract and additional information

Posted November 12, 2007

3:40 pm - 4:30 pm Lockett 381 Originally scheduled for 3:40 pm, Wednesday, November 21, 2007
Boris Rubin, Louisiana State University

Spherical Means in Odd Dimensions and EPD equations.

I am planning to present a simple proof of the

Finch-Patch-Rakesh inversion formula for the spherical mean Radon

transform in odd dimensions. This transform arises in thermoacoustic

tomography. Applications will be given to the Cauchy problem for the

Euler-Poisson-Darboux equation with initial data on the cylindrical surface.

The argument relies on the idea of analytic continuation and properties of

the Erdelyi-Kober fractional integrals. Some open problem will be discussed.

Harmonic Analysis Seminar
Abstract and additional information

Posted February 7, 2008

3:40 pm Lockett 381
Gestur Olafsson, Mathematics Department, LSU

Analysis on Symmetric Spaces

This is a seminar class on homogeneous symmetric spaces G/K, where G is a linear Lie group. We study the basic structure theory for G non-compact. We will then discuss the representation theory related to G/K and harmonic analysis on G/K. In particular we hope to be able to introduce the Fourier transform and, in case G is non-compact, the Radon transform on G/K related to the principal series representations. There is a link to the lecture notes on our webpage http://www.math.lsu,edu/~olafsson/teaching.html

Harmonic Analysis Seminar
Abstract and additional information

Posted February 7, 2008

3:40 pm
Gestur Olafsson, Mathematics Department, LSU

Analysis on Symmetric Spaces

This is a seminar class on homogeneous symmetric spaces G/K, where G is a linear Lie group. We study the basic structure theory for G non-compact. We will then discuss the representation theory related to G/K and harmonic analysis on G/K. In particular we hope to be able to introduce the Fourier transform and, in case G is non-compact, the Radon transform on G/K related to the principal series representations. There is a link to the lecture notes on our webpage http://www.math.lsu,edu/~olafsson/teaching.html

Harmonic Analysis Seminar
Abstract and additional information

Posted February 15, 2008

3:40 pm Lockett 381
Gestur Olafsson, Mathematics Department, LSU

Seminar on Symmetric Sapces

Harmonic Analysis Seminar
Abstract and additional information

Posted February 18, 2008

Last modified February 26, 2008

Hongyu He, Mathematics Department, LSU

Associated Varieties of Irreducible Unitary Representation

Abstract: I will discuss algebraic invariants associated with Irreducible

unitary representations. These invariants will then be used to study the

restrictions of a unitary representation to its subgroups.

Harmonic Analysis Seminar
Abstract and additional information

Posted February 22, 2008

3:40 pm Lockett 381
Gestur Olafsson, Mathematics Department, LSU

Analysis on Symmetric Spaces

This is the third lecture in the series. We will discuss the Iwasawa decomposition of the Lie algebra and the group.

Harmonic Analysis Seminar
Abstract and additional information

Posted February 25, 2008

10:40 am - 11:30 am Lockett 381
Dan Barbasch, Cornell University

Spherical unitary spectrum for split real and p-adic groups.

Abstract: I will give a description of the parametrization of the spherical unitary dual for split groups, and discuss the techniques used to obtain it. The spherical unitary dual is important for problems in harmonic analysis on symmetric spaces and automorphic forms.

Harmonic Analysis Seminar
Abstract and additional information

Posted March 5, 2008

10:40 am - 11:30 am Lockett 381
Joseph Wolf, University of California, Berkeley

Plancherel Formula for Commutative Spaces

Let $(G,K)$ be a Gelfand pair, in other words $G$ is a separable locally compact group, $K$ is a compact subgroup, and the convolution algebra $L^1(K\backslash G/K)$ is commutative. Examples include Riemannian symmetric spaces, locally compact abelian groups and homogeneous graphs. Then the natural representation of $G$ on $L^2(G/K)$ is multiplicity--free and there is a very simple analog of the Euclidean space Fourier transform. I'll describe that transform and the corresponding analog of the Fourier inversion formula.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 1, 2008

10:40 am - 11:30 am Lockett 381
Hongyu He, Department of Mathematics, LSU

Associated Varieties of Irreducible Unitary Representation II

Abstract: I will discuss algebraic invariants associated with Irreducible unitary representations. These invariants will then be used to study the restrictions of a unitary representation to its subgroups.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 4, 2008

10:40 am - 11:30 am Lockett 381
Hongyu He, Mathematics Department, LSU

Associated Varieties of Irreducible Unitary Representation III

Abstract: I will discuss algebraic invariants associated with Irreducible unitary representations. These invariants will then be used to study the restrictions of a unitary representation to its subgroups.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 11, 2008

Last modified April 23, 2008

Milen Yakimov, University of California, Santa Barbara

Reality of representations of rational Cherednik algebras

The Calogero-Moser spaces are the phase spaces of the complexified CM

hamiltonian systems. Recently they also appeared in several different

contexts in representation theory. We will describe a

criterion for reality of representations of rational Cherednik algebras

of type A, which is a class of related algebras. We will then

apply it to study the real locus of a Calogero-Moser space and its

relation to the symplectic geometry of the space. We will finish with

applications to Schubert calculus. (Joint work with Iain Gordon

and Emil Horozov).

Harmonic Analysis Seminar
Abstract and additional information

Posted April 15, 2008

Last modified April 23, 2008

Phuc Nguyen, Purdue University

Singular quasilinear and Hessian equations and inequalities

We give complete characterizations for the solvability of the following quasilinear and Hessian equations: $$ -\Delta_p u = \sigma u^q + \omega, \qquad F_k[-u] = \sigma u^q + \omega, \qquad u \ge 0$$ on a domain Omega\subset\mathbb{R}^n$. Here $\Delta_p$ is the $p$-Laplacian, $F_k[u]$ is the $k$-Hessian, and $\sigma$, $\omega$ are given nonnegative measurable functions (or measures) on $\Omega$. Our results give a complete answer to a problem posed by Bidaut-V\'eron in the case $\sigma\equiv 1$, and extend earlier results due to Kalton and Verbitsky, Brezis and Cabr\'e for general $\sigma$ to nonlinear operators.

This talk is based on joint work with Igor E. Verbitsky.

Harmonic Analysis Seminar
Abstract and additional information

Posted November 24, 2008

3:40 am - 4:30 am Lockett 381
Jens Christensen, Mathematics Department, LSU

A Wavelet Decomposition of Besov Spaces on the Forward Light Cone

Abstract: We will show how the Besov spaces on the Forward Light Cone

(defined for general symmetric cones by Bekolle, Bonami, Garrigos and Ricci)

can be described using wavelet theory. As part of this description we

will discuss work carried out by the presenter and Gestur Olafsson for constructing Banach

spaces using representation theory.

Harmonic Analysis Seminar
Abstract and additional information

Posted January 29, 2009

2:40 pm - 3:30 pm Lockett 381
Dimitar Grantcharov, University of Texas, Arlington

Weight Modules of Affine Lie Algebras

> Abstract: The problem of classifying irreducible weight modules with finite dimensional weight spaces over affine Lie algebras has been studied actively or the last 20 years. Remarkable results include the classification of integrable modules by V. Chari, the study of parabolically induced modules by V. Futorny, and the study of weight modules with bounded weight multiplicities by D. Britten and F. Lemire. There are two important classes of irreducible weight modules with finite dimensional weight spaces: the parabolically induced modules and the loop modules. Several authors made conjectures that would imply that these exhaust all irreducible weight modules with finite dimensional weight spaces. In a joint work with I. Dimitrov we confirm that these conjectures are correct and as a result obtain the classification. In this talk we will present the main ideas and results from our joint work.

Harmonic Analysis Seminar
Abstract and additional information

Posted February 19, 2009

2:40 pm - 3:30 pm Lockett 381
Martin Laubinger, University of Muenster

Groups acting on Trees

The action of $SL(2,\R)$ on the upper half plane is an important tool in the representation theory of $SL(2,\R)$. We explain the $p$-adic analogue, which is an action of $SL(2,Q_p)$ on a tree. This tree is one of the simplest examples of a Bruhat-Tits building. We mention some applications of this action, as well as a generalization: if $K$ is a field with valuation taking values in any ordered abelian group, one can still define a 'tree' associated with $SL(2,K).$

Harmonic Analysis Seminar
Abstract and additional information

Posted March 20, 2009

Last modified March 23, 2009

Daniel Sage, Mathematics Department, LSU

An explicit basis of lowering operators for irreducible representations of unitary groups

> Abstract: It is well-known that the dimensions of irreducible

> representations of unitary groups can be computed in terms of Young

> tableaux. More specifically, each irreducible representation contains

> a unique highest weight which may be interpreted as a Young diagram,

> and the dimension of any weight space of this representation is given

> by the number of semistandard Young tableaux with content determined

> by the weight. In the usual Lie-theoretic construction of these

> representations as highest-weight modules, it is easy to see that a

> spanning set for each representation is obtained by applying lowering

> operators to the highest weight vector; however, extracting a basis

> from this spanning set is less straightforward. In this talk, I

> describe a general method for finding such bases. In particular, I

> show how to associate a monomial lowering operator to any semistandard

> tableau in such a way that the lowering operators corresponding to the

> semistandard tableaux of shape l and content m give rise to a basis

> for the m-weight space of the irreducible representation with highest

> weight l. This work is joint with Larry Smolinsky.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 20, 2009

2:40 pm - 3:30 pm Lockett 381
Boris Rubin, Louisiana State University

Comparison of volumes of convex bodies in real, complex, and quaternionic spaces

The classical Busemann-Petty problem (1956) asks, whether origin-symmetric convex bodies in $R^n$ with smaller hyperplane central sections necessarily have smaller volumes. The answer is known to be affirmative if $n\le 4$ and negative if $n>4$. The same question for equilibrated convex bodies in the $n$-dimensional complex space $C^n$ has an affirmative answer if and only if $n\le 3$. We show that the similar problem in the $n$-dimensional quaternionic space $H^n$ has an affirmative answer if and only if $n=2$. Our method relies on the properties of Radon and cosine transforms on the unit sphere.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 23, 2009

11:00 am - 12:00 pm Lockett 381
Huajun Huang, Auburn University

On Simultaneous Isometry of Subspaces

Let $(V,b)$ be a metric space with a nonsingular symmetric, skew-symmetric, Hermitian, or skew-Hermitian form $b$. Witt's theorem states that an isometry between two subspaces of $V$ can be extended to an isometry of the whole space $V$. In this talk, I will present several results that extend Witt's theorem to simultaneous isometries of subspaces by using matrix analysis techniques. As applications, I will illustrate some examples in isometry groups orbits and invariants. The results could be applied to isometry problems in Hilbert spaces.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 29, 2009

3:40 pm - 4:30 pm Lockett 285
Charles Conley, University of North Texas

Extremal Projectors.

Let g be a complex finite dimensional reductive Lie algebra. The extremal projector P(g) is an element of a certain formal extension of the enveloping algebra U(g) which projects representations in Category O to their highest weight vectors along their lower weight vectors, provided that the denominator of P(g) does not act by zero. (This denominator is a formal product in U(h), h being the chosen Cartan subalgebra.)

In 1971 Asherova-Smirnov-Tolstoi discovered a noncommutative finite factorization of P(g), and in 1993 Zhelobenko discovered a commutative infinite product formula. We will discuss these results and some more recent formulas for the relative projector P(g,l), the projection to the highest l-subrepresentations, l being a Levi subalgebra.

Harmonic Analysis Seminar
Abstract and additional information

Posted November 13, 2009

3:40 pm - 4:30 pm Lockett 381
Boris Rubin, Louisiana State University

Radon Transforms on the Heisenberg Group and Transversal Radon Transforms.

Abstract: The notion of the Radon transform on the Heisenberg group was introduced by R. Strichartz and inspired by D. Geller and E.M. Stein. A more general transversal Radon transform integrates functions on the $m$-dimensional real Euclidean space over hyperplanes meeting the last coordinate axis. We obtain new boundedness results and explicit inversion formulas for both transforms on $L^p$ functions in the full range of the parameter $p$. We also show that these transforms are isomorphisms of the corresponding Semyanistyi-Lizorkin spaces of smooth functions. In the framework of these spaces we obtain inversion formulas, which are pointwise analogues of the corresponding formulas by R. Strichartz.

Harmonic Analysis Seminar
Abstract and additional information

Posted March 4, 2010

1:40 pm - 2:30 pm Lockett 381
Karl Heinrich Hofmann, Darmstadt University, Germany
Professor Emeritus

The probability that two elements commute in a compact group

The FC-center of a group $G$ is the characteristic subgroup $F$ of all elements those conjugacy class is finite. If $G=F$, then $G$ is called an FC-group. We show that a compact group $G$ is an FC-group if and only if its center $Z(G)$ is open (that is, $G$ is center by finite) if and only if its commutator subgroup is finite (that is, $G$ is finite by commutative).Now let $G$ be a compact group and let $p$ denote the Haar measure of the set of all pairs $(x,y)$ in $G\times G$ for which $[x,y]=1$; this is the probability that two randomly picked elements commute. We prove that $p>0$ if and only if the FC-center $F$ of $G$ is open and so has finite index. If these conditions aresatisfied, then $Z(F)$ is a characteristic normal abelian open subgroup of $G$ and $G$ is abelian by finite.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 14, 2010

2:30 pm - 3:20 pm Lockett 381, please note that the times above are sharp
Greg Muller, Cornell University

Calogero-Moser Spaces and Ideals in the Weyl Algebra

The classical nth Calogero-Moser system describes the motion of n-particles

on a line, repelling each other proportional to the inverse-cube of their

separation. This is completely integrable, and can be explicitly solved for

all time; contrast this with inverse-square attraction, which is not

integrable even for 3 particles. If the particles are allowed to have

complex position, then the phase space for this system has a remarkable

compactification, with both an elegant description and unexpected

connections to far-reaches of mathematics. One such connection is that it

parametrizes left ideal classes in the Weyl algebra, the ring of polynomial

differential operators. Time permitting, I will mention how this

observation can be used to construct related systems on other smooth

algebraic curves.

Harmonic Analysis Seminar
Abstract and additional information

Posted August 30, 2010

3:40 pm - 4:30 pm Lockett 381
Ivan Dimitrov, Queen's University (Canada)

Borel subalgebras of gl_\infty

Abstract: The purpose of this talk is to describe all Borel (i.e. all maximal locally solvable) subalgebras of gl_\infty. Consider gl_\infty as the direct limit of gl_n. While the direct limit of Borel subalgebras of gl_n is itself a Borel subalgebra of gl_\infty, the converse is not true. It turns out that the Borel subalgebras of gl_\infty are described rather explicitly as the stabilizers of special chains of subspaces in the natural representation of gl_\infty. I will state the main result and will illustrate it with a number of examples. At the end of the talk I will discuss a couple of open problems. This talk is based on a joint work with Ivan Penkov.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 14, 2010

Last modified September 20, 2010

Karl Heinrich Hofmann, Darmstadt University, Germany
Professor Emeritus

On Spaces Whose Hoemeomorphism Group is Compact

Abstract: This is a seminar lecture between algebra and topology. It deals with the following question: Which compact groups $G$ occur as the full homeomorphism group (with the compact open topology) of a Tychonoff space?

We argue that any such $G$ has to be profinite, that is, totally disconnected. In fact, this is a consequence of a more general result: If a compact but not profinte group acts effectively on a Tychonoff space $X$, then its homeomorphism group $mathcal{H}(X)$ contains a subgroup $H$ and a closed subgroup $K$ which is a normal subgroup of $H$ such that $H/K$ is a topological group which is homeomorphic to a separable Hilbert space $ell^2=ell^2(N)$. Moreover, the quotient map $hrightarrow H/K$ has a topological cross section. Under such circumstances $mathcal{H}(X)$ cannot be locally compact, let alone compact. This is a variation of a theme initiated by James Keesling 1971 by different methods.

In the reverse direction we show that every monothetic (compact) profinite group is the homeomorphism group of a compact connected 1-dimensional space. We conjecture here that every profinite group is (isomorphic to) the homeomorphism group of some compact connected space. A new approach is used here which combines graph theoretical and topological methods initiated more than half a century ago by J. De Groot.

All unfamiliar concepts will by explained in detail.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 29, 2010

3:40 pm - 4:30 pm Lockett 381
Leonardo Mihalcea, Baylor University

Spaces of rational curves in flag manifolds and the quantum Chevalley formula

Abstract: Given Omega a Schubert variety in a flag manifold, one can consider two spaces: the moduli space GW_d(Omega) of rational curves of fixed degree d passing through Omega (a subvariety of the moduli space of stable maps), and the space Gamma_d(\Omega) obtained by taking the union of these curves (a subvariety of the flag manifold). I will show how some simple considerations about the geometry of these spaces leads to a new, natural, proof of the equivariant quantum Chevalley formula proved earlier by Fulton and Woodward and by the speaker. This is joint work with A. Buch.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 20, 2010

3:40 pm - 4:30 pm Lockett 381
Mark Sepanski, Mathematics Department, Baylor University

Distinguished orbits and the L-S category of simply connected compact Lie groups

We show that the Lusternik-Schnirelmann category of a simple, simply connected, compact Lie group G is bounded above by the sum of the relative categories of certain distinguished conjugacy classes in G corresponding to the vertices of the fundamental alcove for the action of the affine Weyl group on the Lie algebra of a maximal torus of G. This is joint work with M. Hunziker.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 6, 2010

3:40 pm - 4:30 pm Lockett 381
Yen Do, Georgia Tech

Variational estimates for paraproducts

Abstract: We generalize a family of variation norm estimates of Lepingle with endpoint estimates of Bourgain and Pisier-Xu to a family of variational estimates for paraproducts, both in the discrete and the continuous setting. This expands on work of Friz and Victoir, our focus being on the continuous case and an expanded range of variation exponents. Some applications in time-frequency analysis are also discussed. Joint work with Camil Muscalu and Christoph Thiele.

Harmonic Analysis Seminar
Abstract and additional information

Posted November 9, 2010

3:40 pm - 4:30 pm Lockett 381
Alexander Fish, University of Wisconsin

Geometric properties of Intersection Body Operator

Abstract: The notion of an intersection body of a star body was introduced by E. Lutwak: K is called the intersection body of L if the radial function of K in every direction is equal to the (d-1)-dimensional volume of the central hyperplane section of L perpendicular to this direction. The notion turned out to be quite interesting and useful in Convex Geometry and Geometric tomography. It is easy to see that the intersection body of a ball is again a ball. E. Lutwak asked if there is any other star-shaped body that satisfies this property. We will present a solution to a local version of this problem: if a convex body K is closed to a unit ball and intersection body of K is equal to K, then K is a unit ball.

Harmonic Analysis Seminar
Abstract and additional information

Posted November 12, 2010

Last modified December 3, 2010

Rodolfo Torres, University of Kansas

Weighted estimates for multilinear singular integrals, commutators, and maximal functions.

Abstract: We will recall a theory of weights developed for multilnear Calder\'on-Zygmund operators and describe some recent related results for the multilinear commutators of singular integrals with point-wise multiplication by BMO functions, their iterations, and new multilinear maximal functions.

Harmonic Analysis Seminar
Abstract and additional information

Posted January 27, 2011

Last modified February 2, 2011

Benjamin Harris, MIT

Fourier Tranforms of Nilpotent, Coadjoint Orbits and Leading Terms of Tempered Characters.

Abstract: Suppose $pi$ is an irreducible, admissible representation of a reductive Lie group with character $Theta_{pi}$. By results of Barbasch-Vogan and Schmid-Vilonen, the leading term of $Theta_{pi}$ at one is an integral linear combination of Fourier transforms of nilpotent coadjoint orbits. The first half of this talk will be about understanding Fourier transforms of nilpotent coadjoint orbits. I will state the most powerful theorem in the subject due to Rossmann and Wallach. Then I will explicitly write down Fourier transforms of nilpotent coadjoint orbits for $text{GL}(n,mathbb{R})$. The second half of this talk will be about understanding which orbits occur in leading terms of characters. In particular, I will state a necessary condition for an orbit to occur in the wave front cycle of a tempered representation. Then I will give an analogue of Kirillov's dimension formula for tempered representations of reductive Lie groups.

Harmonic Analysis Seminar
Abstract and additional information

Posted January 20, 2011

Last modified February 25, 2011

Grigory Litvinov, Independent University of Moscow

INTEGRAL GEOMETRY, HYPERGROUPS AND I.M. GELFAND'S QUESTION

It is well known that the Radon Transform is closely related to the classical Fourier transform and harmonic analysis on the additive groups of finite dimensional real linear spaces. In this talk we discuss ``similar" interrelations between standard problems of Integral Geometry (in the sense of Gelfand and Graev) and harmonic analysis on certain commutative hypergroups (in the sense of J. Delsarte). These interrelations may be interpreted as an answer to an old question of I.M. Gelfand concerning algebraic foundations of Integral Geometry.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 9, 2011

3:40 pm - 4:30 pm Lockett 244
Daniel Maier, University of Tuebingen

Compact Monothetic Groups in Dynamical Systems

Abstract: We give a short introduction in compact monothetic groups and

show the interplay between such groups and dynamical systems.

Especially, we construct measure preserving dynamical systems which are

isomorphic to rotations on compact monothetic groups.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 12, 2011

3:40 pm - 4:30 pm Lockett 244
Karl Heinrich Hofmann, Darmstadt University, Germany
Professor Emeritus

Compact Groups in which any Two Closed Subgroups Commute

We shall discuss compact groups in which any pair of closed subgroups $M$, $N$ satisfies $MN=NM$. After reviewing the existing literature we shall see that it remains to complete the classification by describing profinite metabelian $p$-groups for a prime $p$. The groups we are looking for are quotients of a semidirect product of some power $Z_p^J$ of the additive group of the ring $Z_p$ of $p$-adic integers by the group $Z_p$ acting as the $p$-component of

the group $Z_p^\times$ of units of this ring under scalar multiplication. These quotients are explicitly described. This topic provides the motivation to take a closer look at some of the basic properties of the ring $Z_p$ of p$-adic integers.

Joint work with Francesco Russo, Universit\'a degli studi, Palermo

Harmonic Analysis Seminar
Abstract and additional information

Posted September 26, 2011

Last modified October 17, 2011

Angela Pasquale, University of Metz and CNRS

Reductive dual pairs and orbital integrals on symplectic spaces

Abstract: We present a Weyl integration formula on the symplectic space for a real reductive dual pair. The formula is motivated by the study of the regularity properties of the intertwining distributions of irreducible admissible representations occurring in the Howe correspondence of a reductive dual pair. This is a joint work with M. McKee and T. Przebinda.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 23, 2011

3:40 pm - 4:30 pm Lockett 244
Benjamin Harris, LSU

Limit Formulas for Reductive Lie Groups.

Abstract: Limit formulas for reductive Lie groups were first studied by Gelfand-Graev and Harish-Chandra in connection with the Plancherel formula for reductive Lie groups. Limit formulas for nilpotent orbits are closely related to character theory and invariants of irreducible representations. In this talk, we will discuss some of the things that are known and some of the things that are not known about limit formulas for reductive Lie groups.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 12, 2011

Last modified October 31, 2011

Boris Rubin, Louisiana State University

Philomena Mader's Inversion Formulas for Radon Transforms

Abstract. In 1927 Philomena Mader derived elegant inversion formulas for the hyperplane Radon transform on $R^n$. These formulas differ from the original ones by Johann Radon (1917) and do not need Abel's integral equation or fractional powers of the minus-Laplacian. Surprisingly, these remarkable formulas have been forgotten. We generalize Mader's formulas to totally geodesic Radon transforms in any dimension on arbitrary constant curvature space. This is a joint work with Yuri Antipov.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 26, 2011

Last modified October 28, 2011

Gestur Olafsson, Mathematics Department, LSU

Limits of spherical representations and spherical functions for inductive limits of compact symmetric spaces

Abstract: Spherical representations and functions are the building blocks for harmonic analysis on Riemannian symmetric spaces. We will give a short overview of injective limits of compact symmetric spaces $G_infty/K_infty = varinjlim G_n/K_n$ and limits of spherical representations. We will then describe what happens to the limits of the related spherical $varphi_n (x) = langle e_n, pi_n (x)e_nrangle$ where $e_n$ is a $K_n$--fixed unit vector for $pi_n$. The main result is that the limit $lim_{nto infty} varphi_n(x)$ defines a spherical function on $G_infty /K_infty$ if and only if the rank of $G_n/K_n$ is bounded.

Harmonic Analysis Seminar
Abstract and additional information

Posted January 30, 2012

Last modified February 1, 2012

Ricardo Estrada, Mathematics Department, LSU

Inversion Formulas for the Spherical Means in Constant Curvature Spaces

Abstract: This is a talk on recent work by Boris Rubin, Yuri Antipov and

Ricardo Estrada on inversion formulas for the spherical means. For details

see: arXiv:1107.5992

Harmonic Analysis Seminar
Abstract and additional information

Posted February 6, 2012

Last modified February 15, 2012

Yongdo Lim, Kyungpook National University

Deterministic approaches to the Karcher mean on Hadamard spaces

Abstract: Means on positive matrices and operators have received considerable attention in recent years, particular multivariable and weighted means. Applications have arisen in a variety of areas: approximations, interpolation, filtering, estimation, and averaging, diffusion tensor-MRI, sensor networks, radar signal processing. It has become clear that geometric and metric notions are a vital tool, and the Cartan centroid (least squares mean) on non-positive curved metric spaces plays a key role in metric-based computational algorithms. We discuss some deterministic (i.e., probability-free) approaches to the Cartan centroid on Hadamard spaces.

Harmonic Analysis Seminar
Abstract and additional information

Posted January 25, 2012

Last modified January 26, 2012

Kubo Toshihisa, Oklahoma State University, Stillwater

Conformally Invariant systems of differential operators of non-Heisenberg parabolic type

The wave operator $square$ in Minkowski space $mathbf{R}^{3,1}$ is a classical example of a conformally invariant differential operator. The Lie algebra $mathfrak{so}(4,2)$ acts on $mathbf{R}^{3,1}$ via a multiplier representation $sigma$. When acting on sections of an appropriate bundle over $mathbf{R}^{3,1}$, the elements of $mathfrak{so}(4,2)$ are symmetries of the wave operator $square$; that is, for $X in mathfrak{so}(4,2)$, we have begin{equation*} [sigma(X), square] = C(X) square end{equation*} noindent with $C(X)$ a smooth function on $mathbf{R}^{3,1}$. The notion of conformal invariance for a differential operator appears implicitly and explicitly in the literature. The conformality of one operator has been generalized by Barchini-Kable-Zierau to systems of differential operators. Such systems yield homomrophisms between generalized Verma modules. In this talk we build such systems of first and second-order differential operators in the maximal non-Heisenberg parabolic setting. We also discuss the corresponding homomorphisms between generalized Verma modules.

Harmonic Analysis Seminar
Abstract and additional information

Posted February 15, 2012

3:40 pm - 4:30 pm Lockett 244
Angela Pasquale, University of Metz and CNRS

Estimates for the hypergeometric functions associated with root systems

Harmonic Analysis Seminar
Abstract and additional information

Posted January 20, 2012

Last modified April 19, 2012

Andreas Seeger, University of Wisconsin, Madison

Singular Integrals and a Problem on Mixing

Harmonic Analysis Seminar
Abstract and additional information

Posted August 8, 2012

3:40 pm - 4:30 pm Lockett Hall 285The Fourier and Gegenbauer analysis of fundamental solutions for Laplace's equation on Riemannian spaces of constant curvature

Due to the isotropy of $d$-dimensional hyperbolic and hyperspherical spaces, there exist spherically symmetric fundamental solutions for their corresponding Laplace-Beltrami operators. The $R$-radius hyperboloid model of hyperbolic geometry with $R>0$ represents a Riemannian manifold with negative-constant sectional curvature and the $R$-radius hypersphere emedded in Euclidean space represents a Riemannian manifold with positive-constant sectional curvature. We obtain spherically symmetric fundamental solutions for Laplace's equation on these manifolds in terms of their geodesic radii. We give several matching expressions for these fundamental solutions including definite integral results, finite summation expressions, Gauss hypergeometric functions, and associated Legendre and Ferrers function of the second kind representations. On the $R$-radius hyperbolid we perform Fourier and Gegenbauer analysis for a fundamental solution of Laplace's equation. For instance, in rotationally-invariant coordinate systems, we compute the azimuthal Fourier coefficients for a fundamental solution of Laplace's equation. For $d\ge 2$, we compute the Gegenbauer polynomial expansion in geodesic polar coordinates for a fundamental solution of Laplace's equation on the $R$-radius hyperboloid. In three-dimensions, an addition theorem for the azimuthal Fourier coefficients for a fundamental solution of Laplace's equation is obtained through comparison with its corresponding Gegenbauer expansion. Generalization of this work on the rank one symmetric spaces will be discussed. Short Bio: Dr Howard Cohl obtained a B.S. in Astronomy and Astrophysics from Indiana University, a M.S. and Ph.D. in Physics from Louisiana State University, and a Ph.D. in Mathematics from the University of Auckland in New Zealand. He has worked as a research scientist at various research institutions including the National Solar Observatory in Sunspot, New Mexico; Naval Oceanographic Office Major Shared Resource Center in Stennis Space Center, Mississippi; Lawrence Livermore National Laboratory in Livermore, California; and the School of Physics, University of Exeter in Exeter, United Kingdom. Howard started in December 2010, as a National Research Council Postdoctoral Research Associate in the Applied and Computational Mathematics Division at the National Institute of Standards and Technology. Dr Cohl is currently interested in the special functions associated with fundamental solutions for linear partial differential equations on Riemannian manifolds.

Harmonic Analysis Seminar
Abstract and additional information

Posted August 21, 2012

Last modified August 31, 2012

Boris Rubin, Louisiana State University

Weighted norm inequatlities for $k$-plane transforms

Abstract.

We obtain sharp weighted norm inequalities for the $k$-plane transform,

the ``$j$-plane to $k$-plane'' transform, and the corresponding dual

transforms, acting on $L^p$ spaces with a radial power weight. These

transforms are well known in integral geometry and harmonic analysis.

The operator norms are explicitly evaluated. Some generalizations and

open problems will be discussed.

The paper is available in arXiv:1207.5180v1.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 14, 2012

2:30 pm - 3:20 pm Lockett 284
Raul Quiroga, Centro de Investigacion en Matematicas (cimat)

Commutative C*-algebras of Toeplitz operators and their geometric aspects, Part 1

Abstract Our main object of interest are the Toeplitz operators on weighted Bergman spaces over complex bounded domains. Such operators are given by a ultiplication operator (by a measurable bounded symbol) followed by the Bergman projection. These operators generalize those considered in Hardy spaces and also naturally appear in Berezin's quantization procedure. We will explain a rather unexpected fact: the existence of large and rich families of symbols that define commutative C*-algebras of Toeplitz operators on weighted Bergman spaces. It is also found that Berezin's quantization implies that any such commutative C*-algebra always carries a distinguished geometric structure. We will see how the use of such geometric structure allows to classify the symbols that define commutative C*-algebras on all weighted Bergman spaces on the unit disk. These geometric tools have also provided some interesting constructions for Reinhardt domains and the n-dimensional unit ball.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 14, 2012

2:30 pm - 3:20 pm Lockett 284
Raul Quiroga, Centro de Investigacion en Matematicas (cimat)

Commutative C*-algebras of Toeplitz operators and their geometric aspects, Part 2

Abstract Our main object of interest are the Toeplitz operators on weighted Bergman spaces over complex bounded domains. Such operators are given by a ultiplication operator (by a measurable bounded symbol) followed by the Bergman projection. These operators generalize those considered in Hardy spaces and also naturally appear in Berezin's quantization procedure. We will explain a rather unexpected fact: the existence of large and rich families of symbols that define commutative C*-algebras of Toeplitz operators on weighted Bergman spaces. It is also found that Berezin's quantization implies that any such commutative C*-algebra always carries a distinguished geometric structure. We will see how the use of such geometric structure allows to classify the symbols that define commutative C*-algebras on all weighted Bergman spaces on the unit disk. These geometric tools have also provided some interesting constructions for Reinhardt domains and the n-dimensional unit ball.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 26, 2012

2:30 pm - 3:20 pm Lockett 284
Moritz Egert, University of Darmstadt

Square roots of elliptic systems

We study a system $A$ of $2$nd-order elliptic differential equations on the whole space. We realize $A$ as a maximal-accretive operator on $L^2$. It turns out that in this setting, $A$ admits a unique maximal-accretive square root $A^{\frac{1}{2}}$ that shares an astonishing regularity property: Its domain allows for one weak derivative although the domain of the full operator $A$ does not allow for the expected two weak derivatives in general. As a consequence, the Riesz transform $\nabla A^{-\frac{1}{2}}$ is a bounded operator on $L^2$. Finally, we study the Riesz transform on the $L^p$-scale ($p \in (1,\infty)$) culminating in Auscher's characterization of those $p$ for which the Riesz transform extends to a bounded operator on $L^p$.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 10, 2012

Last modified October 12, 2012

Angela Pasquale, University of Metz and CNRS

Resonances and meromorphic continuation of the resolvent of the Laplace operator on Riemannian symmetric spaces of the noncompact type

Abstract: Let $Delta$ be the Laplace-Beltrami operator on a symmetric space of the noncompact type $G/K$, and let $sigma(Delta)$ denote its spectrum. The resolvent $R(z)=(Delta-z)^{-1}$ is a holomorphic function on $mathbb C setminus sigma(Delta)$, with values in the space of bounded operators on L^2(G/K)$. We study the meromorphic continuation of $R$ as distribution valued map on a Riemann surface above $mathbb C setminus sigma(Delta)$. If such a meromorphic continuation is possible, then the poles of the meromorphically extended resolvent are called the resonances. If $dim X$ is odd and all Cartan subgroups of $G$ are conjugate, then there are no resonances. This can be seen as a consequence of Huygens'principle for the modified wave equation on $X$. In other examples the resonances exist and can be explicitly determined. This is a work in progress with Joachim Hilgert and Tomasz Przebinda.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 9, 2012

Last modified October 12, 2012

Pierre Clare, Penn State University

C*-algebraic normalised intertwiners

Normalised intertwining integrals related to principal series are central objects in representation theory. The aim of this talk is to describe how to construct and study analogous objects at the level of Hilbert modules and C*-algebras that arise when considering the (reduced) dual of a Lie group from the point of view of noncommutative geometry. Some results appear to carry a similar flavour to recent advances in the classical geometric approach.

Harmonic Analysis Seminar
Abstract and additional information

Posted March 19, 2013

3:30 pm - 4:20 pm Lockett 284
Karl Heinrich Hofmann, Darmstadt University, Germany
Professor Emeritus

Transitive actions of a compact group on a locally contractible space: a Theorem by Janos Szenthe revisited and recast

Abstract: In 1974, J. Szenthe published a theorem according to which a compact group which acts faithfully and transitively on a locally contractible space is a Lie group. This theorem was widely used in the sequel. In 2011, Sergey Antonyan discovered that one lemma claimed and essentially used in the original presentation was irretrievably false. So Szenthe's important theorem was open again. I shall report how in a joint paper with Linus Kramer of the University of Munster (Germany) a proof of Senthe's theorem recovers the result as originally stated. Antonyan and Dobrowolski submitted a paper a few days ago which presents a proof dierent from ours. A preprint of A. A George Michael surfaced in november of last year with another proof similar theirs.

Harmonic Analysis Seminar
Abstract and additional information

Posted January 24, 2013

3:30 pm - 4:20 pm tba

Matthew Dawson, Centro de Investigacion en Matematicas

TBA

Harmonic Analysis Seminar
Abstract and additional information

Posted January 24, 2013

Last modified April 10, 2013

Joachim Hilgert, Paderborn University

Fock spaces and small representations

Harmonic Analysis Seminar
Abstract and additional information

Posted June 20, 2013

3:30 pm Lockett 381
Toshihisa Kubo

Construction of explicit homomorphisms between generalized Verma modules

Abstract: In this talk we study constructions of explicit homomorphisms between generalized Verma modules(equivalently, to construct explicit covariant differential operators between homogeneous vector bundles). We in particular show that there is a certain connection between constructions of such homomorphisms and a classic work of Wallach on the analytic continuation of holomorphic discrete series representations.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 10, 2013

Last modified September 11, 2013

Matthew Dawson, Centro de Investigacion en Matematicas

Conical Representations of Direct-Limit Groups

Abstract: Motivated in part by physics, infinite-dimensional Lie groups have been studied more deeply over the past few decades. Due partially to the fact that they are not locally compact and thus do not possess Haar measures, there is currently no general theory of representations and harmonic analysis for infinite-dimensional Lie groups. However, much progress has been made in specific cases. In particular, direct limits of (finite-dimensional) Lie groups provide the simplest examples of infinite-dimensional Lie groups. We overview of some of some of the surprising properties of direct-limit groups and present some recent results related to the classification of conical and spherical representations for direct limits of compact Riemannian symmetric spaces.

Harmonic Analysis Seminar
Abstract and additional information

Posted November 19, 2013

3:30 pm - 4:20 pm Lockett 235
Boris Rubin, Louisiana State University

On the Overdeterminicity in Integral Geometry

Abstract: A simple example of an $n$-dimensional admissible complex of planes is given for the overdetermined $k$-plane transform in $\bbr^n$. Existence of the corresponding restricted $k$-plane transform on $L^p$ functions and explicit inversion formulas are discussed. Similar questions are studied for overdetermined Radon type transforms on the sphere and the hyperbolic space. A theorem describing the range of the restricted $k$-plane transform on the space of rapidly decreasing smooth functions is proved.

Harmonic Analysis Seminar
Abstract and additional information

Posted January 9, 2014

Last modified January 20, 2014

Palle Jorgensen, University of Iowa

Cross roads of stochastic processes, representations of Lie groups, and their applications in physics

Harmonic Analysis Seminar
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Posted March 17, 2014

3:30 pm - 4:20 pm Lockett 235
Raul Quiroga, Centro de Investigacion en Matematicas (cimat)

Commutative algebras generated by Toeplitz operators

Abstract: For a bounded symmetric domain $D$ we define the (weighted) Bergman spaces and their Toeplitz operators. The latter are given by multiplication operators followed by an orthogonal projection. We will also exhibit non-trivial and large commutative algebras generated by spaces of Toeplitz operators. All our examples will be seen to be closely related to the geometry of $D$ and to the holomorphic discrete series of the group of biholomorphisms of $D$.

Harmonic Analysis Seminar
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Posted October 22, 2014

Last modified October 23, 2014

Boris Rubin, Louisiana State University

Gegenbauer-Chebyshev Integrals and Radon Transforms

We suggest new modifications of Helgason's support theorems and related characterizations of the kernel (the null space) for the classical hyperplane Radon transform and its dual, the totally geodesic transforms on the sphere and the hyperbolic space, the spherical slice transform, and the spherical mean transform for spheres through the origin. The assumptions for functions are close to minimal and formulated in integral terms. The proofs rely on projective equivalence of these transforms and new facts for the Gegenbauer-Chebyshev fractional integrals.

Harmonic Analysis Seminar
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Posted February 27, 2015

3:30 pm - 4:20 pm Lockett 277
Eli V Roblero-Mendez, LSU

Rigidity of actions of simple Lie groups, I

ABSTRACT: In this talk we'll give an introduction to Rigidity Theory and the study of actions of simple Lie groups on manifolds which preserve some geometric structure. We'll also give an overview on some recent results obtained in Zimmer's Program and some techniques of how these results have been obtained.

Harmonic Analysis Seminar
Abstract and additional information

Posted February 27, 2015

Last modified March 4, 2015

Eli V Roblero-Mendez, LSU

Rigidity of actions of simple Lie group, II

ABSTRACT: In this talk we'll give an introduction to Rigidity Theory and the study of actions of simple Lie groups on manifolds which preserve some geometric structure. We'll also give an overview on some recent results obtained in Zimmer's Program and some techniques of how these results have been obtained.

Harmonic Analysis Seminar
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Posted November 5, 2015

3:30 pm - 4:20 pm Lockett 277
Amer Darweesh, LSU

Wavletes, Coorbit Theory, and Projective Representation.

Harmonic Analysis Seminar
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Posted March 1, 2017

2:30 pm - 3:20 pm Lockett 136
Kenny De Commer, Vrije Universiteit Brussel

Central approximation properties for quantum groups

Abstract: Several approximation properties for discrete groups (Haagerup property, weak amenability, property (T), ...) can be formulated also for discrete quantum groups, which are Hopf algebras with an involution and integral, to be seen as the group algebra of the discrete quantum group. In this talk, I will explain how one can formulate an extra condition on the approximation properties called centrality, which is automatically satisfied in the discrete group case. We will then show how these central approximation properties have good permanence properties for discrete quantum groups, and will illustrate the theory by showing that the free orthogonal quantum groups of Wang and Van Daele have the Haagerup property and are weakly amenable. If time permits, we will also comment on recent results by Y. Arano and by S. Popa and S. Vaes. This is joint work with A. Freslon and M. Yamashita.

Harmonic Analysis Seminar
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Posted March 13, 2017

Last modified March 14, 2017

Stefan Kolb, Newcastle University

Radial part calculations for affine sl2.

Abstract: In their seminal work in the 70s Olshanetsky and Perelomov used

radial part calculations for symmetric spaces to prove integrability of

the Calogero-Moser Hamiltonian for special parameters. In this talk I will

explain these notions. Then, restricting to affine sl2, I will try to

explain what happens if one extends their argument to Kac-Moody algebras.

One obtains a blend of the KZB-heat equation with Inozemtsev's extension

of the elliptic Calogero-Moser Hamiltonian.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 24, 2017

3:30 pm - 4:20 pm Lockett 285
Hongyu He, Department of Mathematics, LSU

Interlacing relations in Representation theory

Given an irreducible representation of U(n) with highest weight $\lambda$, its restriction to U(n-1) decomposes into a direct sum of irreducible representations of U(n-1) with highest weights $\mu$. It is well-known that $\lambda$ and $\mu$ must satisfy the Cauchy interlacing relations $$\lambda_1 \geq \mu_1 \geq \lambda_2 \geq \mu_2...$$ and vice versa. In this talk, I shall discuss the noncompact analogue for the discrete series of $U(p,q)$ as conjectured by Gan, Gross and Prasad. I will introduce the Gan-Gross-Prasad interlacing relations and discuss some recent progress.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 27, 2017

Last modified October 16, 2017

Reflection Positivity; Representation Theory meets CQFT

Moved by one week: We will give an overview over our work with K-H. Neeb on reflection positivity. We start with recalling the Osterwalder-Schrader Axioms for Constructive Quantum Field Theory and the Osterwalder-Schrader (OS) quantization. We then point out the natural generalization and discuss some examples. We then discuss reflection positive representations, in particular reflection positive 1-parameter subgroups. In the second part we discuss OS quantization related to the sphere.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 27, 2017

Last modified October 16, 2017

Reflection Positivity; Representation Theory meets CQFT, part II

This is the second part of the series on Reflection positivity. Both talks are accessible for graduate students.

Harmonic Analysis Seminar
Abstract and additional information

Posted October 10, 2017

3:30 pm - 4:30 pm Lockett 285
Boris Rubin, Louisiana State University

Weighted Norm Estimates for Radon Transforms and Geometric Inequalities

We obtain sharp inequalities for the Euclidean k-plane transforms and the " j-plane to k-plane'' transforms acting in $L^p$ spaces on $R^n$ with a radial power weight. The corresponding operator norms are explicitly evaluated. The results extend to Funk-type transforms on the sphere and Grassmann manifolds. As a consequence, we obtain new weighted estimates of measures of planar sections for measurable subsets of $R^n$. The corresponding unweighted $L^p -L^q$ estimates and related open problems will be discussed.

Harmonic Analysis Seminar
Abstract and additional information

Posted November 14, 2017

3:30 pm - 4:20 pm Lockett 285
Anton Zeitlin, LSU

Enumerative geometry and quantum integrable systems

Abstract: The miraculous correspondence between 3-dimensional Gauge theory and integrable models based on quantum groups was observed by Nekrasov and Shatashvili in 2009. That discovery led to a lot of interesting developments in mathematics, in particular in enumerative geometry, bringing a new life to older ideas of Givental, and enriching it with flavors of geometric representation theory via the results of Braverman, Maulik, Okounkov and many others. In this talk I will focus on recent breakthroughs, originating from the work of Okounkov on the subject, leading to proper mathematical understanding of Nekrasov-Shatashvili original papers.

Harmonic Analysis Seminar
Abstract and additional information

Posted November 14, 2017

3:30 pm - 4:20 pm Lockett 285
Anton Zeitlin, LSU

Enumerative geometry and quantum integrable systems

Abstract: The miraculous correspondence between 3-dimensional Gauge theory and integrable models based on quantum groups was observed by Nekrasov and Shatashvili in 2009. That discovery led to a lot of interesting developments in mathematics, in particular in enumerative geometry, bringing a new life to older ideas of Givental, and enriching it with flavors of geometric representation theory via the results of Braverman, Maulik, Okounkov and many others. In this talk I will focus on recent breakthroughs, originating from the work of Okounkov on the subject, leading to proper mathematical understanding of Nekrasov-Shatashvili original papers.

Harmonic Analysis Seminar
Abstract and additional information

Posted December 7, 2017

3:30 pm - 4:20 pm Lockett 285
Kenny De Commer, Vrije Universiteit Brussel

Three categorical pictures for quantum symmetric spaces

Abstract: Using Tannaka-Krein methods, a duality can be constructed between actions of a compact quantum group on the one hand, and module C*-categories over its representation category on the other. In this talk, we will construct three module C*-categories for the q-deformed representation category of a compact semisimple Lie group G, starting from a compact symmetric space G/K for G. The first construction is based on the theory of cyclotomic KZ-equations developed by B. Enriquez. The second construction uses the notion of quantum symmetric pair as developed by G. Letzter. The third construction uses the notion of twistedHeisenberg algebra. In all cases, we show that the module C*-category is twist-braided - this is due to B. Enriquez in the first case, S. Kolb in the second case, and closely related to work of J. Donin, P. Kulish and A. Mudrov in the third case. We formulate a conjecture concerning equivalence of these twist-braided module C*-categories, and prove the equivalence in the simplest case of quantum SU(2). This is joint work with S. Neshveyev, L. Tuset and M. Yamashita.

Harmonic Analysis Seminar
Abstract and additional information

Posted February 5, 2018

3:30 pm - 4:30 pm Lockett 243
Raul Quiroga, Centro de Investigacion en Matematicas (cimat)

K-invariant Toeplitz operators on bounded symmetric domains

Harmonic Analysis Seminar
Abstract and additional information

Posted March 21, 2018

3:30 pm - 4:20 pm Lockett 243
Joseph Grenier, Louisiana State University

Constructive and Topological Reflection Positivities

In the 1970''s, Osterwalder and Schrader introduced an axiom for Constructive Quantum Field Theories called Reflection Positivity. The uses and consequence of Reflection Positivity have been explored by Jaffe, Neeb, Olafsson, and more with numerous interesting results. It was only recently, in 2016, that Reflection Positivity was adapted to Topological Quantum Field Theory through the use of bordisms and categories. This talk will briefly introduce the constructive form of Reflection Positivity before discussing the categorical approach taken by Freed and Hopkins. The talk will be suitable for graduate students in algebra, analysis and topology.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 12, 2018

3:30 pm - 4:20 pm Lockett 232
Andreas Debrouwere, LSU

Factorization of quasianalytic vectors

For the abstract see: http://www.math.lsu.edu/~olafsson/Abstract_Debrouwere.pdf

Harmonic Analysis Seminar
Abstract and additional information

Posted September 12, 2018

Last modified September 18, 2018

Jiuyi Zhu, LSU

Quantitative unique continuation of partial differential equations

Abstract: Motivated by the study of eigenfunctions, we consider the quantitative unique continuation (or quantitative uniqueness) of partial differential equations. The quantitative unique continuation is characterized by the order of vanishing of solutions, which describes quantitative behavior of strong unique continuation property. Strong unique continuation property states that if a solution that vanishes of infinite order at a point vanishes identically. It is interesting to know how the norms of the potential functions and gradient potentials control the order of vanishing. We will report some recent progresses about quantitative unique continuation in different Lebesgue spaces for semilinear elliptic equations, parabolic equations and higher order elliptic equations.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 28, 2018

3:30 pm - 4:20 pm Lockett 232
Alexey Karapetyants, Southern Federal University, Russia and SUNY Albany

Mixed norm spaces of analytic functions as spaces of generalized fractional derivatives of functions in Hardy type spaces

We present a new general approach to the definition of a class of mixed norm spaces of analytic functions on the unit disc in complex plane. We study a problem of boundedness of Bergman projection in this general setting. We apply this general approach for the new concrete cases when the norms of variable exponent Lebesgue space, Orlicz space or generalized Morrey space are used. In general, such introduced spaces are the spaces of functions which are in a sense the generalized Hadamard type derivatives of analytic functions having lq summable Taylor coefficients.

Harmonic Analysis Seminar
Abstract and additional information

Posted September 12, 2018

Last modified October 30, 2018

Anton Zeitlin, LSU

Thoughts on Supermoduli

Abstract: I will talk about various approaches to supermoduli spaces of punctured surfaces. After short introduction, I will briefly describe earlier results, regarding the construction of Penner-like coordinates on super-Teichmueller spaces for punctured surfaces. Then I will describe a "parallel" construction explicitly describing deformations of superconformal structures via data on fatgraphs and the associated Strebel differentials.

Harmonic Analysis Seminar
Abstract and additional information

Posted February 3, 2019

3:30 pm - 4:20 pm Lockett 276
Boris Rubin, Louisiana State University

Radon Transforms for Mutually Orthogonal Affine Planes

Abstract: We study a Radon-like transform that takes functions on the Grassmannian of j-dimensional affine planes in $R^n$ to functions on a similar manifold of k-dimensional planes by integration over the set of all j-planes that meet a given k-plane at a right angle. This transform has a mixed structure, combining the k-plane transform and the dual j-plane transform. The main results include action of such transforms on rotation invariant functions, sharp existence conditions, intertwining properties, connection with Riesz potentials and inversion formulas. The case j+k=n-1 for n odd was considered by S. Helgason and F. Gonzalez. This is a joint work with Yingzhan Wang (Guangzhou University).

Harmonic Analysis Seminar
Abstract and additional information

Posted February 11, 2019

3:30 pm - 4:20 pm Lockett 276
Andreas Debrouwere, LSU

The solution to the first Cousin problem for classes of quasianalytic functions

The solution to the (first) Cousin problem on Stein open sets is a classical result in the theory of functions of several complex variables. As a consequence, the Cousin problem is solvable for the class of real analytic functions on an arbitrary open set of R^d. The aim of this talk is to explain this problem and show that it is solvable for general classes of quasianalytic functions. Our solution makes use of the so-called Mittag-Leffler procedure, which will also be discussed during the talk.

Harmonic Analysis Seminar
Abstract and additional information

Posted March 7, 2019

3:30 pm - 4:20 pm Lockett 276
Jens Christensen, Colgate University

Mean Value Operators

Abstract: Mean value operators have many uses in mathematics. They can be used to characterize harmonic functions, and several generalization of mean value operators have been used in the theory of PDEs. The operators are a special type of Radon transforms, and they show up in thermo and photo acoustic tomography. In this talk we will study mapping properties of spherical mean value operators. Our main result is that any smooth function (on a non-compact symmetric space of rank one) can be written as the spherical mean value of another smooth function. The work builds on results by Ehrenpreis regarding division in Paley-Wiener space.

Harmonic Analysis Seminar
Abstract and additional information

Posted March 23, 2019

3:30 pm - 4:20 pm Lockett 276
Joachim Hilgert, Paderborn University

Helgason''s conjecture revisited

Abstract: Helgason''s conjecture from 1976 said that for generic spectral parameters of a Riemannian symmetric space of non-compact type the corresponding Poisson transform is a bijection between hyperfunction sections of the corresponding principal series (realized on the Furstenberg boundary) and the joint eigenfunctions on the symmetric space. The conjecture was settled in a famous paper by Kashiwara-Kowata-Kimura-Okamoto-Oshima-Tanaka in 1978 using heavy machinery from the so-called algebraic analysis started by Mikio Sato. In the 1980s Oshima sketched an alternative approach using less machinery. The key issue is the construction of boundary values of joint eigenfunctions In this talk I will explain a construction of boundary values in the spirit of Oshima as worked out in recent joint work with Soenke Hansen and Aprameyan Parthasarathy.

Harmonic Analysis Seminar
Abstract and additional information

Posted April 9, 2019

3:30 pm - 4:20 pm Lockett 276Some Applications of Harmonic Analysis to Toeplitz Operators for Bounded Symmetric Domains

Abstract: In this talk, we will review some recent advances in the theory of Toeplitz operators defined on Bergman spaces of holomorphic functions on complex bounded symmetric domains. These results were made possible by applying the powerful machinery of harmonic analysis and representation theory. In particular, we will see how the problems of finding large commuting families of Toeplitz operators and of calculating the spectra of Toeplitz operators in such families is closely related to the structure of the scalar-type holomorphic discrete series representations of Hermitian Lie groups.

Harmonic Analysis Seminar
Abstract and additional information

Posted January 21, 2020

2:30 pm - 3:20 pm Lockett 235
Sergio Carrillo, Universidad Sergio Arboleda, Bogata, Columbia

Gevrey power series solutions in analytic functions of first order holomorphic PDEs

Abstract: The goal of this talk is to explain a new Gevrey type -in an analytic function P- for formal power series solutions of some families of singular first order holomorphic PDEs. We will show that under a suitable geometric condition, if P generates the singular locus of the equation, then P is the generic source of divergence of the formal solution. In fact, our result recovers sistematically many well-known cases of singularly perturbed holomorhpic ODEs. The key estimates we use are based on Nagumo norms and their compatibilty with a Weierstrass division theorem. This work is a first step into the study of a Borel-type summability for these series as we shall describe by examples for the case P equal to a monomial.

Harmonic Analysis Seminar
Abstract and additional information

Posted February 7, 2020

Last modified February 16, 2020

Gestur Olafsson, Mathematics Department, LSU

Toeplitz operators and representation theory I

We will discuss the basic ideas how representation theory can be used in the Theory of Toeplitz operators. We start with a general set up of a group acting on a complex manifold with a quasi-invariant measure such that there are non-trivial holomorphic L^2-functions and discuss how that leads to Toeplitz operators. We then introduce several examples. We then connect this to representation theory and explain how representation theory can be used to obtain commutative C^*-algebras of Toeplitz operators. Finally we describe how those ideas can be used to determine the spectrum of the so obtained C^*-algebra by constructing an isomorphism into a L^2-space which is easier to understand. The talks should be accessible to graduate students. We will at least use two seminar talks for the material.

Most of this material is a joint work with M. Dawson and R. Quiroga.

Harmonic Analysis Seminar
Abstract and additional information

Posted February 7, 2020

Last modified February 16, 2020

Gestur Olafsson, Mathematics Department, LSU

Toeplitz operators and representation theory II

We will discuss the basic ideas how representation theory can be used in the Theory of Toeplitz operators. We start with a general set up of a group acting on a complex manifold with a quasi-invariant measure such that there are non-trivial holomorphic L^2-functions and discuss how that leads to Toeplitz operators. We then introduce several examples. We then connect this to representation theory and explain how representation theory can be used to obtain commutative C^*-algebras of Toeplitz operators. Finally we describe how those ideas can be used to determine the spectrum of the so obtained C^*-algebra by constructing an isomorphism into a L^2-space which is easier to understand. The talks should be accessible to graduate students. We will at least use two seminar talks for the material.

Most of this material is a joint work with M. Dawson and R. Quiroga.

Harmonic Analysis Seminar
Abstract and additional information

Posted June 3, 2020

Last modified June 8, 2020

Gestur Olafsson, Mathematics Department, LSU

Toeplitz operators and representation theory III

We will discuss the basic ideas how representation theory can be used in the Theory of Toeplitz operators. We start with a general set up of a group acting on a complex manifold with a quasi-invariant measure such that there are non-trivial holomorphic L^2-functions and discuss how that leads to Toeplitz operators. We then introduce several examples. We then connect this to representation theory and explain how representation theory can be used to obtain commutative C^*-algebras of Toeplitz operators. Finally we describe how those ideas can be used to determine the spectrum of the so obtained C^*-algebra by constructing an isomorphism into a L^2-space which is easier to understand. The talks should be accessible to graduate students. We will at least use two seminar talks for the material.

Most of this material is a joint work with M. Dawson and R. Quiroga.

Harmonic Analysis Seminar
Abstract and additional information

Posted June 15, 2020

3:30 pm - 4:30 pm zoom link: https://lsu.zoom.us/j/99528757270?pwd=SUprWlJyczd3VUhEZ3Z3MTJjdjlwdz09
Gestur Olafsson, Mathematics Department, LSU

Toeplitz operators and representation theory IV

Most of this material is a joint work with M. Dawson and R. Quiroga.

Harmonic Analysis Seminar
Abstract and additional information

Posted June 15, 2020

3:30 pm - 4:30 pm zoom link: https://lsu.zoom.us/j/99528757270?pwd=SUprWlJyczd3VUhEZ3Z3MTJjdjlwdz09
Gestur Olafsson, Mathematics Department, LSU

Toeplitz operators and representation theory V

Harmonic Analysis Seminar
Abstract and additional information

Posted June 15, 2020

3:30 pm - 4:30 pm zoom link: https://lsu.zoom.us/j/99528757270?pwd=SUprWlJyczd3VUhEZ3Z3MTJjdjlwdz09
Jens Christensen, Colgate University

Atomic decompositions of Bergman spaces

In the 1980''s Coifman and Rochberg provided atomic decompositions for Bergman spaces on (the unbounded realization of) bounded symmetric domains as well as on the unit ball. Their atoms were point evaluations of the Bergman kernel. Also, their results did not readily transfer to the bounded realization of the domain except in the case of the unit ball. By applying representation/coorbit theory we obtain a large family of new atoms (including the classical ones) for Bergman spaces on bounded symmetric domains. Our approach also allows us to describe the relation between atoms for the bounded and unbounded realizations of the domain thus solving one of the issues raised by Coifman and Rochberg. We finally list a few open questions for domains of rank higher than one. This is joint work with Gestur Olafsson.

Harmonic Analysis Seminar
Abstract and additional information

Posted July 6, 2020

3:30 pm - 4:30 pm zoom link: https://lsu.zoom.us/j/99528757270?pwd=SUprWlJyczd3VUhEZ3Z3MTJjdjlwdz09
Jens Christensen, Colgate University

Atomic decompositions of Bergman spaces II

In the 1980''''s Coifman and Rochberg provided atomic decompositions for Bergman spaces on (the unbounded realization of) bounded symmetric domains as well as on the unit ball. Their atoms were point evaluations of the Bergman kernel. Also, their results did not readily transfer to the bounded realization of the domain except in the case of the unit ball. By applying representation/coorbit theory we obtain a large family of new atoms (including the classical ones) for Bergman spaces on bounded symmetric domains. Our approach also allows us to describe the relation between atoms for the bounded and unbounded realizations of the domain thus solving one of the issues raised by Coifman and Rochberg. We finally list a few open questions for domains of rank higher than one. This is joint work with Gestur Olafsson.

Harmonic Analysis Seminar
Abstract and additional information

Posted July 20, 2020

Last modified July 28, 2020

Matthew Dawson, Centro de Investigacion en Matematicas

Infinite-dimensional groups and virtual root systems

The study of infinite-dimensional Lie groups and Lie algebras is a growing area of mathematics with interesting connections to mathematical physics and harmonic analysis. In this talk we will focus mainly on such groups and Lie algebras that are constructed from finite-dimensional Lie groups and Lie algebras via direct limits. This allows one to construct infinite-dimensional analogues of the classical groups that are nonetheless of countable dimension (so that they are, in some sense, the "smallest" infinite-dimensional Lie groups that can be constructed). They inherit many properties of their finite-dimensional counterparts, but present new phenomena only seen in infinite-dimensional groups. We will finish with a discussion of ongoing joint work with Johanna Hennig on the structure of certain direct limits of semisimple Lie algebras that are known not to possess root-space decompositions in the traditional sense. Nonetheless, we construct a "virtual root-space decomposition" by way of direct integrals, a tool from harmonic analysis.

Harmonic Analysis Seminar
Abstract and additional information

Posted July 20, 2020

Last modified July 28, 2020

Matthew Dawson, Centro de Investigacion en Matematicas

Infinite-dimensional groups and virtual root systems

The study of infinite-dimensional Lie groups and Lie algebras is a growing area of mathematics with interesting connections to mathematical physics and harmonic analysis. In this talk we will focus mainly on such groups and Lie algebras that are constructed from finite-dimensional Lie groups and Lie algebras via direct limits. This allows one to construct infinite-dimensional analogues of the classical groups that are nonetheless of countable dimension (so that they are, in some sense, the "smallest" infinite-dimensional Lie groups that can be constructed). They inherit many properties of their finite-dimensional counterparts, but present new phenomena only seen in infinite-dimensional groups. We will finish with a discussion of ongoing joint work with Johanna Hennig on the structure of certain direct limits of semisimple Lie algebras that are known not to possess root-space decompositions in the traditional sense. Nonetheless, we construct a "virtual root-space decomposition" by way of direct integrals, a tool from harmonic analysis.

Harmonic Analysis Seminar
Abstract and additional information

Posted July 20, 2020

3:30 pm - 4:30 pm zoom link: https://lsu.zoom.us/j/99528757270?pwd=SUprWlJyczd3VUhEZ3Z3MTJjdjlwdz09
Vignon Oussa, Bridgewater State University

HRT conjecture and linear independence of translates on the Heisenberg group.

In this talk, we will establish the relationship between the HRT Conjecture and linear independence of translation systems on the Heisenberg group. We will show that the HRT Conjecture is equivalent to the conjecture that co-central translates of square-integrable functions on the Heisenberg group are linearly independent. This result affirmatively answers a question asked at the HRT workshop in Saint Louis University in 2016