## Lie Groups and Representation Theory

Seminar information archive ～09/18｜Next seminar｜Future seminars 09/19～

Date, time & place | Tuesday 16:30 - 18:00 126Room #126 (Graduate School of Math. Sci. Bldg.) |
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**Seminar information archive**

### 2024/09/11

13:30-14:30 Room #122 (Graduate School of Math. Sci. Bldg.)

Joint with FJ-LMI seminar.

Counting limit theorems for representations of Gromov-hyperbolic groups (English)

Joint with FJ-LMI seminar.

**Çağrı SERT**(Univeristy of Warwick)Counting limit theorems for representations of Gromov-hyperbolic groups (English)

[ Abstract ]

Let Г be a Gromov-hyperbolic group and S a finite symmetric generating set. The choice of S determines a metric on Г (namely the graph metric on the associated Cayley graph).

Given a representation ρ: Г→GL_d(R), we are interested in obtaining probabilistic limit theorems for the deterministic sequence of spherical averages (with respect to S-metric) for various numerical quantities (such as the operator norm) associated to elements of Г via the representation. We will discuss a general law of large numbers and more refined limit theorems such as central limit theorem and large deviations. Time permitting, connections with the results of Lubotzky–Mozes–Raghunathan and Kaimanovich–Kapovich–Schupp will also be mentioned. Joint work with Stephen Cantrell.

Let Г be a Gromov-hyperbolic group and S a finite symmetric generating set. The choice of S determines a metric on Г (namely the graph metric on the associated Cayley graph).

Given a representation ρ: Г→GL_d(R), we are interested in obtaining probabilistic limit theorems for the deterministic sequence of spherical averages (with respect to S-metric) for various numerical quantities (such as the operator norm) associated to elements of Г via the representation. We will discuss a general law of large numbers and more refined limit theorems such as central limit theorem and large deviations. Time permitting, connections with the results of Lubotzky–Mozes–Raghunathan and Kaimanovich–Kapovich–Schupp will also be mentioned. Joint work with Stephen Cantrell.

### 2023/06/13

17:00-18:00 Room #online (Graduate School of Math. Sci. Bldg.)

Examples of discrete branching laws of derived functor modules (Japanese)

**Yoshiki Oshima**(The University of Tokyo)Examples of discrete branching laws of derived functor modules (Japanese)

[ Abstract ]

We consider the restriction of Zuckerman's derived functor modules for symmetric pairs of real reductive groups assuming that it is discretely decomposable in the sense of Kobayashi. By using a classification result, it can be shown that the restriction decomposes as a direct sum of Zuckerman's derived functor modules for the subgroup. In the last talk, by using the realization of representations as D-modules, a decomposition of Zuckerman's modules corresponding to an orbit decomposition of flag varieties was explained. In this talk, we would like to see that such a decomposition can be written as a direct sum of Zuckerman's modules of the subgroup in some concrete examples.

We consider the restriction of Zuckerman's derived functor modules for symmetric pairs of real reductive groups assuming that it is discretely decomposable in the sense of Kobayashi. By using a classification result, it can be shown that the restriction decomposes as a direct sum of Zuckerman's derived functor modules for the subgroup. In the last talk, by using the realization of representations as D-modules, a decomposition of Zuckerman's modules corresponding to an orbit decomposition of flag varieties was explained. In this talk, we would like to see that such a decomposition can be written as a direct sum of Zuckerman's modules of the subgroup in some concrete examples.

### 2023/06/06

17:30-18:30 Room #056 (Graduate School of Math. Sci. Bldg.)

Joint with Tuesday Seminar on Topology

Visible actions on reductive spherical homogeneous spaces and their invariant measures

(Japanese)

Joint with Tuesday Seminar on Topology

**Atsumu Sasaki**(Tokai University)Visible actions on reductive spherical homogeneous spaces and their invariant measures

(Japanese)

[ Abstract ]

Toshiyuki Kobayashi has established propagation theorem of multiplicity-freeness property.

This theorem enables us to give an unified explanation of multiplicity-freeness of multiplicity-free representations which have been found so far, and also to find new examples of multiplicity-free representations systematically. Kobayashi further has introduced the notion of visible actions on complex manifolds as a basic condition for propagation theorem of multiplicity-freeness property. This notion plays an important role to this theorem and also brings us to find various decomposition theorems of Lie groups and homogeneous spaces.

In this talk, we explain visible actions on reductive spherical homogeneous spaces. In particular, we see that for a visible action on reductive spherical homogeneous space our construction of a submanifold which meets every orbit (called a slice) is given by an explicit description of a Cartan decomposition for this space. As a corollary of this study, we characterize the invariant measure on a reductive spherical homogeneous space by giving an integral formula for a Cartan decomposition explicitly.

Toshiyuki Kobayashi has established propagation theorem of multiplicity-freeness property.

This theorem enables us to give an unified explanation of multiplicity-freeness of multiplicity-free representations which have been found so far, and also to find new examples of multiplicity-free representations systematically. Kobayashi further has introduced the notion of visible actions on complex manifolds as a basic condition for propagation theorem of multiplicity-freeness property. This notion plays an important role to this theorem and also brings us to find various decomposition theorems of Lie groups and homogeneous spaces.

In this talk, we explain visible actions on reductive spherical homogeneous spaces. In particular, we see that for a visible action on reductive spherical homogeneous space our construction of a submanifold which meets every orbit (called a slice) is given by an explicit description of a Cartan decomposition for this space. As a corollary of this study, we characterize the invariant measure on a reductive spherical homogeneous space by giving an integral formula for a Cartan decomposition explicitly.

### 2023/05/30

17:00-18:00 Room #online (Graduate School of Math. Sci. Bldg.)

Discrete branching laws of derived functor modules (Japanese)

**Yoshiki Oshima**(The University of Tokyo)Discrete branching laws of derived functor modules (Japanese)

[ Abstract ]

We consider the restriction of Zuckerman's derived functor modules for symmetric pairs of real reductive groups assuming that it is discretely decomposable in the sense of Kobayashi. By using a classification result, it can be shown that the restriction decomposes as a direct sum of Zuckerman's derived functor modules for the subgroup. In this talk, we would like to discuss how to obtain explicit branching formulas for some examples.

We consider the restriction of Zuckerman's derived functor modules for symmetric pairs of real reductive groups assuming that it is discretely decomposable in the sense of Kobayashi. By using a classification result, it can be shown that the restriction decomposes as a direct sum of Zuckerman's derived functor modules for the subgroup. In this talk, we would like to discuss how to obtain explicit branching formulas for some examples.

### 2023/05/23

17:00-18:00 Room #online (Graduate School of Math. Sci. Bldg.)

Deformation of the heat kernel and the Wiener measure from the viewpoint of Laguerre semigroup theory (Japanese)

**Temma Aoyama**(The University of Tokyo)Deformation of the heat kernel and the Wiener measure from the viewpoint of Laguerre semigroup theory (Japanese)

[ Abstract ]

I talk about basic properties of generalized heat kernels and a construction of generalized Wiener measures form the viewpoint of Laguerre semigroup theory and generalized Fourier analysis introduced by B. Saïd--T. Kobayashi--B. Ørsted.

I talk about basic properties of generalized heat kernels and a construction of generalized Wiener measures form the viewpoint of Laguerre semigroup theory and generalized Fourier analysis introduced by B. Saïd--T. Kobayashi--B. Ørsted.

### 2023/05/16

17:00-18:00 Room #online (Graduate School of Math. Sci. Bldg.)

Integral expression of the $(k,a)$-generalized Laguerre semigroup

(Japanese)

**Hiroyoshi TAMORI**(Shibaura institute of technology)Integral expression of the $(k,a)$-generalized Laguerre semigroup

(Japanese)

[ Abstract ]

The $(k,a)$-generalized Laguerre semigroup was introduced by Ben

Sa\"{\i}d--Kobayashi-{\O}rsted as an interpolation of the Hermite semigroup (the k=0, a=2 case) and the Laguerre semigroup (the k=0, a=1 case). Based on a joint work with Kouichi Taira (Ritsumeikan University), I will explain an integral expression of the semigroup and an upper estimate of the integral kernel, which leads to Strichartz estimates for operators $|x|^{2-a}\Delta_{k}-|x|^a$ and $|x|^{2-a}\Delta_{k}$ ($\Delta_k$ denotes the Dunkl Laplacian) under some condition on the deformation parameter $(k,a)$.

The $(k,a)$-generalized Laguerre semigroup was introduced by Ben

Sa\"{\i}d--Kobayashi-{\O}rsted as an interpolation of the Hermite semigroup (the k=0, a=2 case) and the Laguerre semigroup (the k=0, a=1 case). Based on a joint work with Kouichi Taira (Ritsumeikan University), I will explain an integral expression of the semigroup and an upper estimate of the integral kernel, which leads to Strichartz estimates for operators $|x|^{2-a}\Delta_{k}-|x|^a$ and $|x|^{2-a}\Delta_{k}$ ($\Delta_k$ denotes the Dunkl Laplacian) under some condition on the deformation parameter $(k,a)$.

### 2022/06/28

17:00-18:00 Room #online (Graduate School of Math. Sci. Bldg.)

Computation of weighted Bergman inner products on bounded symmetric domains and Plancherel-type formulas for $(Sp(2r,\mathbb{R}),Sp(r,\mathbb{R})\times Sp(r,\mathbb{R}))$ (Japanese)

**Ryosuke Nakahama**(Kyushu University)Computation of weighted Bergman inner products on bounded symmetric domains and Plancherel-type formulas for $(Sp(2r,\mathbb{R}),Sp(r,\mathbb{R})\times Sp(r,\mathbb{R}))$ (Japanese)

[ Abstract ]

Let $(G,G_1)=(G,(G^\sigma)_0)$ be a symmetric pair of holomorphic type, and we consider a pair of Hermitian symmetric spaces $D_1=G_1/K_1\subset D=G/K$, realized as bounded symmetric domains in complex vector spaces $\mathfrak{p}^+_1:=(\mathfrak{p}^+)^\sigma\subset\mathfrak{p}^+$ respectively. Then the universal covering group $\widetilde{G}$ of $G$ acts unitarily on the weighted Bergman space $\mathcal{H}_\lambda(D)\subset\mathcal{O}(D)=\mathcal{O}_\lambda(D)$ on $D$ for sufficiently large $\lambda$. Its restriction to the subgroup $\widetilde{G}_1$ decomposes discretely and multiplicity-freely, and its branching law is given explicitly by Hua--Kostant--Schmid--Kobayashi's formula in terms of the $\widetilde{K}_1$-decomposition of the space $\mathcal{P}(\mathfrak{p}^+_2)$ of polynomials on $\mathfrak{p}^+_2:=(\mathfrak{p}^+)^{-\sigma}\subset\mathfrak{p}^+$. Our goal is to understand the decomposition of the restriction $\mathcal{H}_\lambda(D)|_{\widetilde{G}_1}$ by studying the weighted Bergman inner product on each $\widetilde{K}_1$-type in $\mathcal{P}(\mathfrak{p}^+_2)\subset\mathcal{H}_\lambda(D)$.

Today we mainly deal with the symmetric pair $(G,G_1)=(Sp(2r,\mathbb{R}),Sp(r,\mathbb{R})\times Sp(r,\mathbb{R}))$.

Let $(G,G_1)=(G,(G^\sigma)_0)$ be a symmetric pair of holomorphic type, and we consider a pair of Hermitian symmetric spaces $D_1=G_1/K_1\subset D=G/K$, realized as bounded symmetric domains in complex vector spaces $\mathfrak{p}^+_1:=(\mathfrak{p}^+)^\sigma\subset\mathfrak{p}^+$ respectively. Then the universal covering group $\widetilde{G}$ of $G$ acts unitarily on the weighted Bergman space $\mathcal{H}_\lambda(D)\subset\mathcal{O}(D)=\mathcal{O}_\lambda(D)$ on $D$ for sufficiently large $\lambda$. Its restriction to the subgroup $\widetilde{G}_1$ decomposes discretely and multiplicity-freely, and its branching law is given explicitly by Hua--Kostant--Schmid--Kobayashi's formula in terms of the $\widetilde{K}_1$-decomposition of the space $\mathcal{P}(\mathfrak{p}^+_2)$ of polynomials on $\mathfrak{p}^+_2:=(\mathfrak{p}^+)^{-\sigma}\subset\mathfrak{p}^+$. Our goal is to understand the decomposition of the restriction $\mathcal{H}_\lambda(D)|_{\widetilde{G}_1}$ by studying the weighted Bergman inner product on each $\widetilde{K}_1$-type in $\mathcal{P}(\mathfrak{p}^+_2)\subset\mathcal{H}_\lambda(D)$.

Today we mainly deal with the symmetric pair $(G,G_1)=(Sp(2r,\mathbb{R}),Sp(r,\mathbb{R})\times Sp(r,\mathbb{R}))$.

### 2022/05/17

17:00-18:00 Room #on line (Graduate School of Math. Sci. Bldg.)

Estimate of the optimal constant of convolution inequalities on unimodular

locally compact groups

(Japanese)

**Takashi Satomi**(The University of Tokyo)Estimate of the optimal constant of convolution inequalities on unimodular

locally compact groups

(Japanese)

[ Abstract ]

Some convolution inequalities (Young's inequality, the reverse Young's inequality, the Hausdorff--Young inequality) known for a long time on $\mathbb{R}$ can be generalized for any unimodular locally compact group.

In this seminar, we estimate the optimal constants (the ratio of both sides such that these inequalities are optimal) of these inequalities from above and below, and discuss that these estimates are the best for $G=\mathbb{R}$.

Some convolution inequalities (Young's inequality, the reverse Young's inequality, the Hausdorff--Young inequality) known for a long time on $\mathbb{R}$ can be generalized for any unimodular locally compact group.

In this seminar, we estimate the optimal constants (the ratio of both sides such that these inequalities are optimal) of these inequalities from above and below, and discuss that these estimates are the best for $G=\mathbb{R}$.

### 2022/05/10

17:00-18:00 Room #on line (Graduate School of Math. Sci. Bldg.)

Holomorphic multiplier representations over bounded homogeneous domains (Japanese)

**Koichi Arashi**(Nagoya University)Holomorphic multiplier representations over bounded homogeneous domains (Japanese)

[ Abstract ]

I will talk about unitarizations in the spaces of holomorphic sections of equivariant holomorphic line bundles over bounded homogeneous domains. We consider the identity components of algebraic groups acting transitively on the domains. The main part of this talk is a classification of such unitary representations.

We discuss an explicit description of the classification for a specific five-dimensional non-symmetric bounded homogeneous domain to illustrate the method of the classification (K. Arashi, "Holomorphic multiplier representations for bounded homogeneous domains", Journal of Lie Theory 30, 1091-1116 (2020)).

I will talk about unitarizations in the spaces of holomorphic sections of equivariant holomorphic line bundles over bounded homogeneous domains. We consider the identity components of algebraic groups acting transitively on the domains. The main part of this talk is a classification of such unitary representations.

We discuss an explicit description of the classification for a specific five-dimensional non-symmetric bounded homogeneous domain to illustrate the method of the classification (K. Arashi, "Holomorphic multiplier representations for bounded homogeneous domains", Journal of Lie Theory 30, 1091-1116 (2020)).

### 2022/04/26

17:00-18:00 Room #online (Graduate School of Math. Sci. Bldg.)

Joint with Tuesday Seminar on Topology

On the existence of discrete series for homogeneous spaces (Japanese)

Joint with Tuesday Seminar on Topology

**Yoshiki Oshima**(The University of Tokyo)On the existence of discrete series for homogeneous spaces (Japanese)

[ Abstract ]

When a Lie group $G$ acts transitively on a manifold $X$, an irreducible subrepresentation of $L^2(X)$ is called a discrete series representation of $X$. One may ask which homogeneous space $X$ has a discrete series representation. For reductive symmetric spaces, it is known that the existence of discrete series is equivalent to a rank condition by works of Flensted-Jensen, T.Matsuki, and T.Oshima. The problem for general reductive homogeneous spaces was considered by T.Kobayashi and a sufficient condition for the existence of discrete series was obtained by using his theory of admissible restriction. In this talk, we would like to

see another sufficient condition for general homogeneous spaces and also the case of their line bundles in terms of the orbit method.

When a Lie group $G$ acts transitively on a manifold $X$, an irreducible subrepresentation of $L^2(X)$ is called a discrete series representation of $X$. One may ask which homogeneous space $X$ has a discrete series representation. For reductive symmetric spaces, it is known that the existence of discrete series is equivalent to a rank condition by works of Flensted-Jensen, T.Matsuki, and T.Oshima. The problem for general reductive homogeneous spaces was considered by T.Kobayashi and a sufficient condition for the existence of discrete series was obtained by using his theory of admissible restriction. In this talk, we would like to

see another sufficient condition for general homogeneous spaces and also the case of their line bundles in terms of the orbit method.

### 2022/04/19

17:30-18:30 Room #online (Graduate School of Math. Sci. Bldg.)

Joint with Tuesday Seminar on Topology

On the classification and construction of conformal symmetry breaking operators for anti-de Sitter spaces

(Japanese)

Joint with Tuesday Seminar on Topology

**Toshihisa Kubo**(Ryukoku University)On the classification and construction of conformal symmetry breaking operators for anti-de Sitter spaces

(Japanese)

[ Abstract ]

Let $X$ be a smooth manifold and $Y$ a smooth submanifold of $X$. Take $G' \subset G$ to be a pair of Lie groups that act on $Y \subset X$, respectively. Consider a $G'$-intertwining differential operator $\mathcal{D}$ from the space of smooth sections for a $G$-equivariant vector bundle over $X$ to that for a $G'$-equivariant vector bundle over $Y$. Toshiyuki Kobayashi called such a differential operator $\mathcal{D}$ a \emph{differential symmetry breaking operator} (differential SBO for short)

([T. Kobayashi, Differential Geom. Appl. (2014)]).

In [Kobayashi-K-Pevzner, Lecture Notes in Math. 2170 (2016)], we explicitly constructed and classified all the differential SBOs from the space of differential $i$-forms $\mathcal{E}^i(S^n)$ over the standard

Riemann sphere $S^n$ to that of differential $j$-forms $\mathcal{E}^j(S^{n-1})$ over the totally geodesic hypersphere $S^{n-1}$.

In this talk, by extending the results in a Riemannian setting, we discuss about the classification and construction of differential SBOs in a pseudo-Riemannian setting such as anti-de Sitter spaces and hyperbolic spaces. This is a joint work with Toshiyuki Kobayashi and Michael Pevzner.

Let $X$ be a smooth manifold and $Y$ a smooth submanifold of $X$. Take $G' \subset G$ to be a pair of Lie groups that act on $Y \subset X$, respectively. Consider a $G'$-intertwining differential operator $\mathcal{D}$ from the space of smooth sections for a $G$-equivariant vector bundle over $X$ to that for a $G'$-equivariant vector bundle over $Y$. Toshiyuki Kobayashi called such a differential operator $\mathcal{D}$ a \emph{differential symmetry breaking operator} (differential SBO for short)

([T. Kobayashi, Differential Geom. Appl. (2014)]).

In [Kobayashi-K-Pevzner, Lecture Notes in Math. 2170 (2016)], we explicitly constructed and classified all the differential SBOs from the space of differential $i$-forms $\mathcal{E}^i(S^n)$ over the standard

Riemann sphere $S^n$ to that of differential $j$-forms $\mathcal{E}^j(S^{n-1})$ over the totally geodesic hypersphere $S^{n-1}$.

In this talk, by extending the results in a Riemannian setting, we discuss about the classification and construction of differential SBOs in a pseudo-Riemannian setting such as anti-de Sitter spaces and hyperbolic spaces. This is a joint work with Toshiyuki Kobayashi and Michael Pevzner.

### 2022/04/05

17:00-17:30 Room #online (Graduate School of Math. Sci. Bldg.)

Note on the restriction of minimal representations with respect to reductive symmetric pairs (Japanese)

**Toshiyuki KOBAYASHI**(The University of Tokyo)Note on the restriction of minimal representations with respect to reductive symmetric pairs (Japanese)

[ Abstract ]

I discuss briefly some abstract feature of branching problems with focus on the restriction of minimal representations with respect to reductive symmetric pairs.

I discuss briefly some abstract feature of branching problems with focus on the restriction of minimal representations with respect to reductive symmetric pairs.

### 2022/04/05

17:30-18:30 Room #online (Graduate School of Math. Sci. Bldg.)

Estimate of the norm of the $L^p$-Fourier transform on compact extensions of locally compact groups

(Japanese)

**Junko INOUE**(Tottori University)Estimate of the norm of the $L^p$-Fourier transform on compact extensions of locally compact groups

(Japanese)

[ Abstract ]

The classical Hausdorff-Young theorem for locally compact abelian groups is generalized by Kunze for unimodular locally compact groups.

When the group $G$ is of type I, the abstract Plancherel theorem gives a decomposition of the regular representation into a direct integral of irreducible representations through the Fourier transform;

By the Hausdorff-Young theorem generalized by Kunze, for exponents $p$ $(1 < p \leq 2)$ and ${p'}=p/(p-1)$, the Fourier transform yields a bounded operator $\mathcal{F}^p:L^p(G)\to L^{p'}(\widehat{G})$, where $L^{p'}(\widehat{G})$ is the $L^{p'}$ space of measurable fields of the Schatten class operators on the unitary dual $\widehat{G}$ of $G$.

Under this setting, we are concerned with the norm $\|\mathcal{F}^p(G)\|$ of the $L^p$-Fourier transform $\mathcal{F}^p$.

Let $G$ be a separable unimodular locally compact group of type I,and $N$ be a type I, unimodular, closed normal subgroup of $G$. Suppose $G/N$ is compact. Then we show the inequality $\|\mathcal{F}^p(G)\|\leq\|\mathcal F^p(N)\|$ for $1< p \leq 2$.

This result is a joint work with Ali Baklouti

(J. Fourier Anal. Appl. 26 (2020), Paper No. 26).

The classical Hausdorff-Young theorem for locally compact abelian groups is generalized by Kunze for unimodular locally compact groups.

When the group $G$ is of type I, the abstract Plancherel theorem gives a decomposition of the regular representation into a direct integral of irreducible representations through the Fourier transform;

By the Hausdorff-Young theorem generalized by Kunze, for exponents $p$ $(1 < p \leq 2)$ and ${p'}=p/(p-1)$, the Fourier transform yields a bounded operator $\mathcal{F}^p:L^p(G)\to L^{p'}(\widehat{G})$, where $L^{p'}(\widehat{G})$ is the $L^{p'}$ space of measurable fields of the Schatten class operators on the unitary dual $\widehat{G}$ of $G$.

Under this setting, we are concerned with the norm $\|\mathcal{F}^p(G)\|$ of the $L^p$-Fourier transform $\mathcal{F}^p$.

Let $G$ be a separable unimodular locally compact group of type I,and $N$ be a type I, unimodular, closed normal subgroup of $G$. Suppose $G/N$ is compact. Then we show the inequality $\|\mathcal{F}^p(G)\|\leq\|\mathcal F^p(N)\|$ for $1< p \leq 2$.

This result is a joint work with Ali Baklouti

(J. Fourier Anal. Appl. 26 (2020), Paper No. 26).

### 2022/03/08

17:00-18:00 Room #online (Graduate School of Math. Sci. Bldg.)

On the structure of Hamiltonian G-varieties (Japanese)

**Masatoshi Kitagawa**(Waseda University)On the structure of Hamiltonian G-varieties (Japanese)

[ Abstract ]

I will talk about a result by I. Losev (Math. Z. 2009) on the structure of Hamiltonian G-varieties.

In particular, I will explain how to reduce the result to central-nilpotent cases.

I will give an application of the result to branching laws.

I will talk about a result by I. Losev (Math. Z. 2009) on the structure of Hamiltonian G-varieties.

In particular, I will explain how to reduce the result to central-nilpotent cases.

I will give an application of the result to branching laws.

### 2022/02/22

17:00-18:00 Room #online (Graduate School of Math. Sci. Bldg.)

On a long exact sequence of the Schwartz homology (Japanese)

**Hiroyoshi Tamori**(Hokkaido University)On a long exact sequence of the Schwartz homology (Japanese)

[ Abstract ]

For a smooth Fr\’{e}chet representation of moderate growth of an almost linear Nash group, Chen-Sun introduced a homology (called Schwartz homology) equipped with certain topology. Given a short exact sequence of such representations, we can construct a long exact sequence of Schwartz homology groups via the natural isomorphism with relative Lie algebra homology. We give an example of a long exact sequence where the connecting homomorphism is not continuous.

For a smooth Fr\’{e}chet representation of moderate growth of an almost linear Nash group, Chen-Sun introduced a homology (called Schwartz homology) equipped with certain topology. Given a short exact sequence of such representations, we can construct a long exact sequence of Schwartz homology groups via the natural isomorphism with relative Lie algebra homology. We give an example of a long exact sequence where the connecting homomorphism is not continuous.

### 2022/02/15

17:00-18:00 Room #online (Graduate School of Math. Sci. Bldg.)

Deformations of standard compact Clifford-Klein forms (Japanese)

**Kazuki Kannaka**(RIKEN iTHEMS)Deformations of standard compact Clifford-Klein forms (Japanese)

[ Abstract ]

Let Γ be a discontinuous group for a homogeneous manifold G/H of reductive type.

The Clifford-Klein form Γ\G/H is standard if Γ is contained in a reductive subgroup of G acting properly on G/H.

For 12 series of standard compact Clifford-Klein forms given by Kobayashi-Yoshino, we discuss in this talk whether or not there exist (1) locally rigid ones, (2) non-standard deformations, and (3) Zariski-dense deformations in G.

After briefly explaining Kobayashi's work and Kassel's work on these

questions, we will explain the new results.

Let Γ be a discontinuous group for a homogeneous manifold G/H of reductive type.

The Clifford-Klein form Γ\G/H is standard if Γ is contained in a reductive subgroup of G acting properly on G/H.

For 12 series of standard compact Clifford-Klein forms given by Kobayashi-Yoshino, we discuss in this talk whether or not there exist (1) locally rigid ones, (2) non-standard deformations, and (3) Zariski-dense deformations in G.

After briefly explaining Kobayashi's work and Kassel's work on these

questions, we will explain the new results.

### 2022/01/18

17:00-18:00 Room #On line (Graduate School of Math. Sci. Bldg.)

Strongly visible actions on complex domains (Japanese)

**Hideyuki Ishi**(Osaka City University)Strongly visible actions on complex domains (Japanese)

[ Abstract ]

In this century, the Cartan-Hartogs domain and its variations, on which the Bergman kernel function and the Kahler-Einstein metric can be computed explicitly, have been actively studied. Reasoning that strongly visible actions on the domains enable such nice calculations, we introduce a new type of complex domain analogous to the Cartan-Hartogs domain, and present a research plan about harmonic analysis over the domain.

In this century, the Cartan-Hartogs domain and its variations, on which the Bergman kernel function and the Kahler-Einstein metric can be computed explicitly, have been actively studied. Reasoning that strongly visible actions on the domains enable such nice calculations, we introduce a new type of complex domain analogous to the Cartan-Hartogs domain, and present a research plan about harmonic analysis over the domain.

### 2022/01/11

17:00-18:00 Room #on line (Graduate School of Math. Sci. Bldg.)

Joint with Tuesday Seminar on Topology.

On the existence problem of Compact Clifford-Klein forms of indecomposable pseudo-Riemannian symmetric spaces with signature (n,2) (Japanese)

Joint with Tuesday Seminar on Topology.

**Keiichi Maeta**(The University of Tokyo)On the existence problem of Compact Clifford-Klein forms of indecomposable pseudo-Riemannian symmetric spaces with signature (n,2) (Japanese)

[ Abstract ]

For a homogeneous space $G/H$ and its discontinuous group $\Gamma\subset G$, the double coset space $\Gamma\backslash G/H$ is called a Clifford-Klein form of $G/H$. In the study of Clifford-Klein forms, the classification of homogeneous spaces which admit compact Clifford-Klein forms is one of the important open problems, which was introduced by Toshiyuki Kobayashi in 1980s.

We consider this problem for indecomposable and reducible pseudo-Riemannian symmetric spaces with signature (n,2). We show the non-existence of compact Clifford-Klein forms for some series of symmetric spaces, and construct new compact Clifford-Klein forms of countably infinite five-dimensional pseudo-Riemannian symmetric spaces with signature (3,2).

For a homogeneous space $G/H$ and its discontinuous group $\Gamma\subset G$, the double coset space $\Gamma\backslash G/H$ is called a Clifford-Klein form of $G/H$. In the study of Clifford-Klein forms, the classification of homogeneous spaces which admit compact Clifford-Klein forms is one of the important open problems, which was introduced by Toshiyuki Kobayashi in 1980s.

We consider this problem for indecomposable and reducible pseudo-Riemannian symmetric spaces with signature (n,2). We show the non-existence of compact Clifford-Klein forms for some series of symmetric spaces, and construct new compact Clifford-Klein forms of countably infinite five-dimensional pseudo-Riemannian symmetric spaces with signature (3,2).

### 2021/12/21

17:30-18:30 Room #on line (Graduate School of Math. Sci. Bldg.)

Joint with Tuesday Seminar on Topology.

Classification of holomorphic vertex operator algebras of central charge 24

(Japanese)

Joint with Tuesday Seminar on Topology.

**Hiroki Shimakura**(Tohoku University)Classification of holomorphic vertex operator algebras of central charge 24

(Japanese)

[ Abstract ]

Holomorphic vertex operator algebras are important in vertex operator algebra theory. For example, the famous moonshine vertex operator algebra is holomorphic.

One of the fundamental problems is to classify holomorphic vertex operator algebras. It is known that holomorphic vertex operator algebras of central charge 8 and 16 are lattice vertex operator algebras.

I will talk about recent progress on the classification of holomorphic vertex operator algebras of central charge 24.

Holomorphic vertex operator algebras are important in vertex operator algebra theory. For example, the famous moonshine vertex operator algebra is holomorphic.

One of the fundamental problems is to classify holomorphic vertex operator algebras. It is known that holomorphic vertex operator algebras of central charge 8 and 16 are lattice vertex operator algebras.

I will talk about recent progress on the classification of holomorphic vertex operator algebras of central charge 24.

### 2021/12/14

17:00-18:00 Room #on line (Graduate School of Math. Sci. Bldg.)

On the definition of Conley indices (Japanese)

**Yosuke Morita**(Kyoto University)On the definition of Conley indices (Japanese)

[ Abstract ]

Conley indices are used to describe local behaviour of topological dynamical systems. In this talk, I will explain a new framework for Conley index theory. Our approach is very elementary, and uses only general topology and some computations of inclusion relations of subsets.

Conley indices are used to describe local behaviour of topological dynamical systems. In this talk, I will explain a new framework for Conley index theory. Our approach is very elementary, and uses only general topology and some computations of inclusion relations of subsets.

### 2021/12/07

17:00-18:00 Room #on line (Graduate School of Math. Sci. Bldg.)

On the classification of the $K$-type formulas for the Heisenberg ultrahyperbolic equation (Japanese)

**Toshihisa Kubo**(Ryukoku University)On the classification of the $K$-type formulas for the Heisenberg ultrahyperbolic equation (Japanese)

[ Abstract ]

About ten years ago, Kable constructed a one-parameter family $\square^{(n)}_s$ ($s\in \mathbb{C}$) of differential operators for $\mathfrak{sl}(n,\mathbb{C})$. He referred to $\square^{(n)}_s$ as the Heisenberg ultrahyperbolic operator. In the viewpoint of intertwining operators, $\square^{(n)}_s$ can be thought of as an intertwining differential operator between certain parabolically induced representations for $\widetilde{SL}(n,\mathbb{R})$. In this talk we discuss about the classification of the $K$-type formulas of the space of $K$-finite solutions to the differential equation $\square^{(3)}_sf=0$ for $\widetilde{SL}(3,\mathbb{R})$ and some related topics. This is joint work with Bent {\O}rsted.

About ten years ago, Kable constructed a one-parameter family $\square^{(n)}_s$ ($s\in \mathbb{C}$) of differential operators for $\mathfrak{sl}(n,\mathbb{C})$. He referred to $\square^{(n)}_s$ as the Heisenberg ultrahyperbolic operator. In the viewpoint of intertwining operators, $\square^{(n)}_s$ can be thought of as an intertwining differential operator between certain parabolically induced representations for $\widetilde{SL}(n,\mathbb{R})$. In this talk we discuss about the classification of the $K$-type formulas of the space of $K$-finite solutions to the differential equation $\square^{(3)}_sf=0$ for $\widetilde{SL}(3,\mathbb{R})$ and some related topics. This is joint work with Bent {\O}rsted.

### 2021/11/30

17:00-18:00 Room #on line (Graduate School of Math. Sci. Bldg.)

Branching problems for conformal Lie groups and orthogonal polynomials (English)

**Quentin Labriet**(Reims University)Branching problems for conformal Lie groups and orthogonal polynomials (English)

[ Abstract ]

In this talk, I will present some results obtained during my PhD about a link between branching problems for conformal Lie groups and orthogonal polynomials. More precisely, I am going to look at some examples of branching problems for representations in the scalar-valued holomorphic discrete series of some conformal Lie groups. Using the geometry of symmetric cone, I will explain how the theory of orthogonal polynomials can be related to branching problems and to the construction of symmetry breaking and holographic operators.

In this talk, I will present some results obtained during my PhD about a link between branching problems for conformal Lie groups and orthogonal polynomials. More precisely, I am going to look at some examples of branching problems for representations in the scalar-valued holomorphic discrete series of some conformal Lie groups. Using the geometry of symmetric cone, I will explain how the theory of orthogonal polynomials can be related to branching problems and to the construction of symmetry breaking and holographic operators.

### 2021/11/23

17:00-18:00 Room #on line (Graduate School of Math. Sci. Bldg.)

A Cartan decomposition for a reductive real spherical subgroup

(Japanese)

**Yuichiro Tanaka**(The University of Tokyo)A Cartan decomposition for a reductive real spherical subgroup

(Japanese)

[ Abstract ]

A closed subgroup H of a real reductive Lie group G is real spherical if a minimal parabolic subgroup of G has an open orbit on G/H.

In this talk I would like to show a proof of a Cartan decomposition G=KAH when H is reductive.

This is a conjecture of T. Kobayashi, introduced in the 3rd Number Theory Summer School in 1995.

A closed subgroup H of a real reductive Lie group G is real spherical if a minimal parabolic subgroup of G has an open orbit on G/H.

In this talk I would like to show a proof of a Cartan decomposition G=KAH when H is reductive.

This is a conjecture of T. Kobayashi, introduced in the 3rd Number Theory Summer School in 1995.

### 2021/11/16

17:00-18:00 Room #on line (Graduate School of Math. Sci. Bldg.)

Computation of weighted Bergman norms on block diagonal matrices in bounded symmetric domains (Japanese)

**Ryosuke Nakahama**(Kyushu University)Computation of weighted Bergman norms on block diagonal matrices in bounded symmetric domains (Japanese)

[ Abstract ]

Let $G/K\simeq D\subset\mathfrak{p}^+$ be a Hermitian symmetric space realized as a bounded symmetric domain, and we consider the weighted Bergman space $\mathcal{H}_\lambda(D)$ on $D$.

Then the norm on each $K$-type in $\mathcal{H}_\lambda(D)$ is explicitly computed by Faraut--Kor\'anyi (1990).

In this talk, we consider the cases $\mathfrak{p}^+=\operatorname{Sym}(r,\mathbb{C})$, $M(r,\mathbb{C})$, $\operatorname{Alt}(2r,\mathbb{C})$, fix $r=r'+r''$, and decompose $\mathfrak{p}^+$ into $2\times 2$ block matrices.

Then the speaker presents the results on explicit computation of the norm of $\mathcal{H}_\lambda(D)$ on each $K'$-type in the space of polynomials on the block diagonal matrices $\mathfrak{p}^+_{11}\oplus\mathfrak{p}^+_{22}$.

Also, as an application, the speaker presents the results on Plancherel-type formulas on the branching laws for symmetric pairs $(Sp(r,\mathbb{R}),U(r',r''))$, $(U(r,r),U(r',r'')\times U(r'',r'))$, $(SO^*(4r),U(2r',2r''))$.

Let $G/K\simeq D\subset\mathfrak{p}^+$ be a Hermitian symmetric space realized as a bounded symmetric domain, and we consider the weighted Bergman space $\mathcal{H}_\lambda(D)$ on $D$.

Then the norm on each $K$-type in $\mathcal{H}_\lambda(D)$ is explicitly computed by Faraut--Kor\'anyi (1990).

In this talk, we consider the cases $\mathfrak{p}^+=\operatorname{Sym}(r,\mathbb{C})$, $M(r,\mathbb{C})$, $\operatorname{Alt}(2r,\mathbb{C})$, fix $r=r'+r''$, and decompose $\mathfrak{p}^+$ into $2\times 2$ block matrices.

Then the speaker presents the results on explicit computation of the norm of $\mathcal{H}_\lambda(D)$ on each $K'$-type in the space of polynomials on the block diagonal matrices $\mathfrak{p}^+_{11}\oplus\mathfrak{p}^+_{22}$.

Also, as an application, the speaker presents the results on Plancherel-type formulas on the branching laws for symmetric pairs $(Sp(r,\mathbb{R}),U(r',r''))$, $(U(r,r),U(r',r'')\times U(r'',r'))$, $(SO^*(4r),U(2r',2r''))$.

### 2021/11/09

17:00-18:00 Room #on line (Graduate School of Math. Sci. Bldg.)

On the support of Plancherel measures and the image of moment map

(Japanese)

**Yoshiki Oshima**(Osaka University)On the support of Plancherel measures and the image of moment map

(Japanese)

[ Abstract ]

We see a relationship between the support of Plancherel measures for homogeneous spaces and the image of moment maps from cotangent bundles based on a joint work with Benjamin Harris.

Moreover, we discuss related problems and conjectures about inductions and restrictions for representations of Lie groups in general settings.

We see a relationship between the support of Plancherel measures for homogeneous spaces and the image of moment maps from cotangent bundles based on a joint work with Benjamin Harris.

Moreover, we discuss related problems and conjectures about inductions and restrictions for representations of Lie groups in general settings.