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過去の記録 ～05/22｜次回の予定｜今後の予定 05/23～
| 担当者 | 小林俊行, ミカエル ペブズナー |
|---|
過去の記録
2025年05月13日(火)
14:30-15:15 数理科学研究科棟(駒場) 002号室
Matthew CELLOT 氏 (University of Lille (France))
Homotopy quantum field theories and 3-types (英語)
https://fj-lmi.cnrs.fr/seminars/
Matthew CELLOT 氏 (University of Lille (France))
Homotopy quantum field theories and 3-types (英語)
[ 講演概要 ]
Quantum topology is a field that came about in the 1980s following remarkable discoveries by Jones, Drinfeld and Witten, whose work dramatically renewed topology, in particular in low dimension. A fundamental notion in quantum topology is that of topological quantum field theory (TQFT) formulated by Witten and Atiyah. This notion originates in ideas from quantum physics and constitutes a framework that organizes certain topological invariants of manifolds, called quantum invariants, which are defined by means of quantum groups. Homotopy quantum field theories (HQFTs) are a generalization of TQFTs. The idea is to use TQFT techniques to study principal bundles over manifolds and, more generally, homotopy classes of maps from manifolds to a (fixed) topological space called the target.
Turaev and Virelizier have recently constructed 3-dimensional HQFTs (by state-sum) when the target space is aspherical (i.e. its n-th homotopy groups are trivial for n>1) and Sözer and Virelizier have constructed 3-dimensional HQFTs when the target space is a 2-type (i.e. its n-th homotopy groups are trivial for n>2). Using state sum techniques, Douglas and Reutter have constructed 4-dimensional TQFTs from spherical fusion 2-categories. In this talk, we combine both these approaches: we construct state sum 4-dimensional HQFTs with a 3-type target from fusion 2-categories graded by a 2-crossed module.
[ 講演参考URL ]Quantum topology is a field that came about in the 1980s following remarkable discoveries by Jones, Drinfeld and Witten, whose work dramatically renewed topology, in particular in low dimension. A fundamental notion in quantum topology is that of topological quantum field theory (TQFT) formulated by Witten and Atiyah. This notion originates in ideas from quantum physics and constitutes a framework that organizes certain topological invariants of manifolds, called quantum invariants, which are defined by means of quantum groups. Homotopy quantum field theories (HQFTs) are a generalization of TQFTs. The idea is to use TQFT techniques to study principal bundles over manifolds and, more generally, homotopy classes of maps from manifolds to a (fixed) topological space called the target.
Turaev and Virelizier have recently constructed 3-dimensional HQFTs (by state-sum) when the target space is aspherical (i.e. its n-th homotopy groups are trivial for n>1) and Sözer and Virelizier have constructed 3-dimensional HQFTs when the target space is a 2-type (i.e. its n-th homotopy groups are trivial for n>2). Using state sum techniques, Douglas and Reutter have constructed 4-dimensional TQFTs from spherical fusion 2-categories. In this talk, we combine both these approaches: we construct state sum 4-dimensional HQFTs with a 3-type target from fusion 2-categories graded by a 2-crossed module.
https://fj-lmi.cnrs.fr/seminars/
2025年04月23日(水)
13:30-14:15 数理科学研究科棟(駒場) 056号室
Alexandre BROUSTE 氏 (Le Mans Université)
Fast and efficient inference for large and high-frequency data (英語)
https://fj-lmi.cnrs.fr/seminars/
Alexandre BROUSTE 氏 (Le Mans Université)
Fast and efficient inference for large and high-frequency data (英語)
[ 講演概要 ]
The theory of Local Asymptotic Normality (LAN), initiated by Lucien Le Cam, provides a powerful framework for studying the asymptotic optimality of estimators. When the LAN property holds for a statistical experiment with a non-singular Fisher information matrix, minimax theorems can be applied, allowing for the derivation of a lower bound for the variance of estimators.
Beyond the classical i.i.d. setting, the LAN property has been established for various statistical models. However, for several high-frequency statistical experiments, only weak LAN properties were derived with a singular Fisher information matrix, preventing the application of minimax theorems. For these experiments, it has also remained unclear for a long time whether the maximum likelihood estimator (MLE) possesses any form of asymptotic optimality.
Moreover, when the MLE achieves optimality, its computation is generally time-consuming, making it challenging for handling large or high-frequency datasets and alternative estimation methods are therefore needed for different applications.
In this talk, we review our previous results obtained with M. Fukasawa on fractional Gaussian noise and H. Masuda on stable processes observed at high frequency as well as the various progress made since then. We also present our efforts to popularize the one-step procedure as a fast and asymptotically efficient alternative to the MLE.
[ 講演参考URL ]The theory of Local Asymptotic Normality (LAN), initiated by Lucien Le Cam, provides a powerful framework for studying the asymptotic optimality of estimators. When the LAN property holds for a statistical experiment with a non-singular Fisher information matrix, minimax theorems can be applied, allowing for the derivation of a lower bound for the variance of estimators.
Beyond the classical i.i.d. setting, the LAN property has been established for various statistical models. However, for several high-frequency statistical experiments, only weak LAN properties were derived with a singular Fisher information matrix, preventing the application of minimax theorems. For these experiments, it has also remained unclear for a long time whether the maximum likelihood estimator (MLE) possesses any form of asymptotic optimality.
Moreover, when the MLE achieves optimality, its computation is generally time-consuming, making it challenging for handling large or high-frequency datasets and alternative estimation methods are therefore needed for different applications.
In this talk, we review our previous results obtained with M. Fukasawa on fractional Gaussian noise and H. Masuda on stable processes observed at high frequency as well as the various progress made since then. We also present our efforts to popularize the one-step procedure as a fast and asymptotically efficient alternative to the MLE.
https://fj-lmi.cnrs.fr/seminars/
2025年04月17日(木)
15:00-15:45 数理科学研究科棟(駒場) 056号室
Pierre SCHAPIRA 氏 (IMJ - Sorbonne University)
Sheaves for spacetime (英語)
https://fj-lmi.cnrs.fr/wp-content/uploads/2025/02/Tokyo25Sem.pdf
Pierre SCHAPIRA 氏 (IMJ - Sorbonne University)
Sheaves for spacetime (英語)
[ 講演概要 ]
We shall study the Cauchy problem on globally hyperbolic manifolds with the only tools of microlocal sheaf theory and the precise Cauchy-Kowalevski theorem.
A causal manifold is a manifold $M$ endowed with a closed convex proper cone $\lambda\subset T^*M$. On such a manifold, one defines the $\lambda$-topology and the associated notion of a causal pre-order. One introduces the notion of a G-causal manifold, those for which there exists a time function. On a G-manifold, sheaves satisfying a suitable condition on their micro-support and defined on a neighborhood of a Cauchy hypersurface extend to the whole space. When the sheaf is the complex of hyperfunction solutions of a hyperbolic $\mathcal D$-module, this proves that the Cauchy problem is globally well-posed.
We will also describe a ``shifted spacetime'' associated with the quantization of an Hamiltonian isotopy.
This talk is partly based on papers in collaboration with Benoît Jubin, Stéphane Guillermou and Masaki Kashiwara.
[ 講演参考URL ]We shall study the Cauchy problem on globally hyperbolic manifolds with the only tools of microlocal sheaf theory and the precise Cauchy-Kowalevski theorem.
A causal manifold is a manifold $M$ endowed with a closed convex proper cone $\lambda\subset T^*M$. On such a manifold, one defines the $\lambda$-topology and the associated notion of a causal pre-order. One introduces the notion of a G-causal manifold, those for which there exists a time function. On a G-manifold, sheaves satisfying a suitable condition on their micro-support and defined on a neighborhood of a Cauchy hypersurface extend to the whole space. When the sheaf is the complex of hyperfunction solutions of a hyperbolic $\mathcal D$-module, this proves that the Cauchy problem is globally well-posed.
We will also describe a ``shifted spacetime'' associated with the quantization of an Hamiltonian isotopy.
This talk is partly based on papers in collaboration with Benoît Jubin, Stéphane Guillermou and Masaki Kashiwara.
https://fj-lmi.cnrs.fr/wp-content/uploads/2025/02/Tokyo25Sem.pdf
2025年04月17日(木)
15:45-16:30 数理科学研究科棟(駒場) 056号室
Giuseppe DITO 氏 (Université Bourgogne Europe)
Deformation quantization and Wightman distributions (英語)
https://fj-lmi.cnrs.fr/seminars/
Giuseppe DITO 氏 (Université Bourgogne Europe)
Deformation quantization and Wightman distributions (英語)
[ 講演概要 ]
Twisted $\hbar$-deformations by classical wave operators are introduced for a scalar field theory in Minkowski spacetime. These deformations are non-perturbative in the coupling constant. The corresponding Wightman $n$-functions are defined as evaluations at $0$ of the $n$-fold deformed products of classical solutions of the classical wave equation. We show that, in this setting, the $2$-point function is well-defined as a formal series in $\hbar$ of tempered distributions. Interestingly, these twisted deformations appear to possess an inherent renormalization scheme.
[ 講演参考URL ]Twisted $\hbar$-deformations by classical wave operators are introduced for a scalar field theory in Minkowski spacetime. These deformations are non-perturbative in the coupling constant. The corresponding Wightman $n$-functions are defined as evaluations at $0$ of the $n$-fold deformed products of classical solutions of the classical wave equation. We show that, in this setting, the $2$-point function is well-defined as a formal series in $\hbar$ of tempered distributions. Interestingly, these twisted deformations appear to possess an inherent renormalization scheme.
https://fj-lmi.cnrs.fr/seminars/
2025年04月14日(月)
17:00-18:00 数理科学研究科棟(駒場) Main Lecture Hall号室
Pierre SCHAPIRA 氏 (IMJ - Sorbonne University)
Microlocal sheaf theory and elliptic pairs (英語)
https://fj-lmi.cnrs.fr/wp-content/uploads/2025/03/Tokyo25Colloq.pdf
Pierre SCHAPIRA 氏 (IMJ - Sorbonne University)
Microlocal sheaf theory and elliptic pairs (英語)
[ 講演概要 ]
On a complex manifold $X$, an elliptic pair $(\mathcal{M},G)$ is the data of a coherent $\mathcal{D}_X$-module $\mathcal{M}$ and an $\mathbb R$-constructible sheaf $G$ with the property that the characteristic variety $\operatorname{char}(\mathcal{M})$ and the micro-support $\mathrm{SS}(G)$ do not intersect outside the zero-section of $T^*X$. We prove a regularity result which generalizes the classical case of hyperfunction solutions of elliptic systems and a finiteness theorem when assuming that the support of the pair is compact.
Then we introduce the microlocal Euler class of $\mathcal{M}$ and that of $G$ and calculate the Euler-Poincar\'e index of the complex of holomorphic solutions of the pair as the integral over $T^*X$ of the cup product of these two characteristic classes. This construction gives a new approach to the Riemann--Roch or the Atiyah--Singer theorems.
I will start by briefly recalling all necessary notions of microlocal sheaf theory and $\mathcal{D}$-module theory.
[ 講演参考URL ]On a complex manifold $X$, an elliptic pair $(\mathcal{M},G)$ is the data of a coherent $\mathcal{D}_X$-module $\mathcal{M}$ and an $\mathbb R$-constructible sheaf $G$ with the property that the characteristic variety $\operatorname{char}(\mathcal{M})$ and the micro-support $\mathrm{SS}(G)$ do not intersect outside the zero-section of $T^*X$. We prove a regularity result which generalizes the classical case of hyperfunction solutions of elliptic systems and a finiteness theorem when assuming that the support of the pair is compact.
Then we introduce the microlocal Euler class of $\mathcal{M}$ and that of $G$ and calculate the Euler-Poincar\'e index of the complex of holomorphic solutions of the pair as the integral over $T^*X$ of the cup product of these two characteristic classes. This construction gives a new approach to the Riemann--Roch or the Atiyah--Singer theorems.
I will start by briefly recalling all necessary notions of microlocal sheaf theory and $\mathcal{D}$-module theory.
https://fj-lmi.cnrs.fr/wp-content/uploads/2025/03/Tokyo25Colloq.pdf
2024年12月04日(水)
14:00-15:00 数理科学研究科棟(駒場) 056号室
Jonathan Ditlevsen 氏 (The University of Tokyo)
Symmetry breaking operators for the pair (GL(n+1,R), GL(n,R)) (英語)
https://fj-lmi.cnrs.fr/seminars/
Jonathan Ditlevsen 氏 (The University of Tokyo)
Symmetry breaking operators for the pair (GL(n+1,R), GL(n,R)) (英語)
[ 講演概要 ]
In this talk, we construct explicit symmetry breaking operators (SBOs) between principal series representations of the group GL(n+1,R) and its subgroup GL(n,R). Using Bernstein–Sato identities, we find a holomorphic renormalization of a meromorphic family of SBOs. Finally, we identify certain differential SBOs as residues of this holomorphic family.
[ 講演参考URL ]In this talk, we construct explicit symmetry breaking operators (SBOs) between principal series representations of the group GL(n+1,R) and its subgroup GL(n,R). Using Bernstein–Sato identities, we find a holomorphic renormalization of a meromorphic family of SBOs. Finally, we identify certain differential SBOs as residues of this holomorphic family.
https://fj-lmi.cnrs.fr/seminars/
2024年11月27日(水)
14:30-15:30 数理科学研究科棟(駒場) 122号室
Ali BAKLOUTI 氏 (University of Sfax)
A proof of the Zariski closure conjecture for coadjoint orbits of exponential Lie groups (英語)
https://fj-lmi.cnrs.fr/seminars/
Ali BAKLOUTI 氏 (University of Sfax)
A proof of the Zariski closure conjecture for coadjoint orbits of exponential Lie groups (英語)
[ 講演概要 ]
I will begin by defining the Zariski Closure Conjecture for coadjoint orbits of exponential solvable Lie groups, examining some cases that have been solved, and addressing the ongoing challenges in resolving the conjecture fully. I will then introduce new approaches to explore the relationship between generating families of primitive ideals and the set of polynomials that vanish on the associated coadjoint orbits, ultimately aiming to advance toward a solution to the conjecture.
[ 講演参考URL ]I will begin by defining the Zariski Closure Conjecture for coadjoint orbits of exponential solvable Lie groups, examining some cases that have been solved, and addressing the ongoing challenges in resolving the conjecture fully. I will then introduce new approaches to explore the relationship between generating families of primitive ideals and the set of polynomials that vanish on the associated coadjoint orbits, ultimately aiming to advance toward a solution to the conjecture.
https://fj-lmi.cnrs.fr/seminars/
2024年11月27日(水)
13:30-14:30 数理科学研究科棟(駒場) 122号室
藤原英徳 氏 (OCAMI, 近畿大学)
Inductions and restrictions of unitary representations for exponential solvable Lie groups. (英語)
https://fj-lmi.cnrs.fr/seminars/
藤原英徳 氏 (OCAMI, 近畿大学)
Inductions and restrictions of unitary representations for exponential solvable Lie groups. (英語)
[ 講演概要 ]
Let $G = \exp \mathfrak g$ be a connected and simply connected real nilpotent Lie group with Lie algebra $\mathfrak g$, $H = \exp \mathfrak h$ an analytic subgroup of $G$ with Lie algebra $\mathfrak h$, $\chi$ a unitary character of $H$ and $\tau = \text{ind}_H^G \chi$ the monomial representation of $G$ induced from $\chi$. Let $D_{\tau}(G/H)$ be the algebra of the $G$-invariant differential operators on the line bundle over $G/H$ associated to the data $(H,\chi)$. We denote by $C_{\tau}$ the center of $D_{\tau}(G/H)$. We know that $\chi$ is written as ${\chi}_f$, where $\chi_f(\exp X) = e^{if(X)} (X \in \mathfrak h)$ with a certain $f \in {\mathfrak g}^*$ verifying $f([\mathfrak h,\mathfrak h]) = \{0\}$. Let $S(\mathfrak g)$ be the symmetric algebra of $\mathfrak g$ and ${\mathfrak a}_{\tau} = \{X + \sqrt{-1}f(X) ; X \in \mathfrak h\}.$ We regard $S(\mathfrak g)$ as the algebra of polynomial functions on ${\mathfrak g}^*$ by $X(\ell) = \sqrt{-1}\ell(X)$ for $X \in \mathfrak g, \ell \in {\mathfrak g}^*$. Now, $S(\mathfrak g)$ possesses the Poisson structure $\{,\}$ well determined by the equality $\{X,Y\} = [X,Y]$ if $X, Y$ are in $\mathfrak g$. Let us consider the algebra $(S(\mathfrak g)/S(\mathfrak g)\overline{{\mathfrak a}_{\tau}})^H$ of the $H$-invariant polynomial functions on the affine subspace ${\Gamma}_{\tau} = \{\ell \in {\mathfrak g}^* : \ell(X) = f(X), X \in \mathfrak h\}$ of ${\mathfrak g}^*$. This inherits the Poisson structure from $S(\mathfrak g)$. We denote by $Z_{\tau}$ its Poisson center. Michel Duflo asked: the two algebras $C_{\tau}$ and $Z_{\tau}$, are they isomorphic? Here we provide a positive answer to this question.
[ 講演参考URL ]Let $G = \exp \mathfrak g$ be a connected and simply connected real nilpotent Lie group with Lie algebra $\mathfrak g$, $H = \exp \mathfrak h$ an analytic subgroup of $G$ with Lie algebra $\mathfrak h$, $\chi$ a unitary character of $H$ and $\tau = \text{ind}_H^G \chi$ the monomial representation of $G$ induced from $\chi$. Let $D_{\tau}(G/H)$ be the algebra of the $G$-invariant differential operators on the line bundle over $G/H$ associated to the data $(H,\chi)$. We denote by $C_{\tau}$ the center of $D_{\tau}(G/H)$. We know that $\chi$ is written as ${\chi}_f$, where $\chi_f(\exp X) = e^{if(X)} (X \in \mathfrak h)$ with a certain $f \in {\mathfrak g}^*$ verifying $f([\mathfrak h,\mathfrak h]) = \{0\}$. Let $S(\mathfrak g)$ be the symmetric algebra of $\mathfrak g$ and ${\mathfrak a}_{\tau} = \{X + \sqrt{-1}f(X) ; X \in \mathfrak h\}.$ We regard $S(\mathfrak g)$ as the algebra of polynomial functions on ${\mathfrak g}^*$ by $X(\ell) = \sqrt{-1}\ell(X)$ for $X \in \mathfrak g, \ell \in {\mathfrak g}^*$. Now, $S(\mathfrak g)$ possesses the Poisson structure $\{,\}$ well determined by the equality $\{X,Y\} = [X,Y]$ if $X, Y$ are in $\mathfrak g$. Let us consider the algebra $(S(\mathfrak g)/S(\mathfrak g)\overline{{\mathfrak a}_{\tau}})^H$ of the $H$-invariant polynomial functions on the affine subspace ${\Gamma}_{\tau} = \{\ell \in {\mathfrak g}^* : \ell(X) = f(X), X \in \mathfrak h\}$ of ${\mathfrak g}^*$. This inherits the Poisson structure from $S(\mathfrak g)$. We denote by $Z_{\tau}$ its Poisson center. Michel Duflo asked: the two algebras $C_{\tau}$ and $Z_{\tau}$, are they isomorphic? Here we provide a positive answer to this question.
https://fj-lmi.cnrs.fr/seminars/
2024年11月13日(水)
13:30-14:30 数理科学研究科棟(駒場) 056号室
Stefano OLLA 氏 (Université de Paris Dauphine - PSL Research University)
Diffusive behaviour in extended completely integrable dynamics (英語)
https://fj-lmi.cnrs.fr/seminars/
Stefano OLLA 氏 (Université de Paris Dauphine - PSL Research University)
Diffusive behaviour in extended completely integrable dynamics (英語)
[ 講演概要 ]
On a diffusive space-time scaling, density fluctuations behave very differently in extended completely integrable systems with respect to chaotic systems. I will expose some recent results concerning the one dimensional hard rods infinite dynamics and the box-ball cellular automata (an ultradiscretization of the KdV equation). Joint works with Pablo Ferrari, Makiko Sasada, Hayate Suda.
[ 講演参考URL ]On a diffusive space-time scaling, density fluctuations behave very differently in extended completely integrable systems with respect to chaotic systems. I will expose some recent results concerning the one dimensional hard rods infinite dynamics and the box-ball cellular automata (an ultradiscretization of the KdV equation). Joint works with Pablo Ferrari, Makiko Sasada, Hayate Suda.
https://fj-lmi.cnrs.fr/seminars/
2024年11月01日(金)
14:00-15:00 数理科学研究科棟(駒場) 126号室
Thomas GILETTI 氏 (Université Clermont-Auvergne)
Propagating behaviour of solutions of multistable reaction-diffusion equations (英語)
https://fj-lmi.cnrs.fr/seminars/
Thomas GILETTI 氏 (Université Clermont-Auvergne)
Propagating behaviour of solutions of multistable reaction-diffusion equations (英語)
[ 講演概要 ]
This talk will be devoted to propagation phenomena for a general scalar reaction-diffusion PDE, when it may admit an arbitrarily large number of stationary states. It is well known that, in some simple cases, special travelling front solutions (depending on a single variable moving with a constant speed) arise in the large time behaviour of solutions. Due to this feature, reaction-diffusion equations have become ubiquituous in the modelling of spatial invasions in ecology, population dynamics and biology. However, in general, large time propagation can no longer be described by a single front, but by a family of several successive fronts (or `propagating terrace') involving intermediate transient equilibria. I will review several methods, including a connection with Sturm-Liouville theory, to handle such dynamics.
[ 講演参考URL ]This talk will be devoted to propagation phenomena for a general scalar reaction-diffusion PDE, when it may admit an arbitrarily large number of stationary states. It is well known that, in some simple cases, special travelling front solutions (depending on a single variable moving with a constant speed) arise in the large time behaviour of solutions. Due to this feature, reaction-diffusion equations have become ubiquituous in the modelling of spatial invasions in ecology, population dynamics and biology. However, in general, large time propagation can no longer be described by a single front, but by a family of several successive fronts (or `propagating terrace') involving intermediate transient equilibria. I will review several methods, including a connection with Sturm-Liouville theory, to handle such dynamics.
https://fj-lmi.cnrs.fr/seminars/
2024年10月02日(水)
13:30-14:30 数理科学研究科棟(駒場) 122号室
Daniel CARO 氏 (Université de Caen Normandie)
Introduction to arithmetic D-modules (英語)
https://fj-lmi.cnrs.fr/seminars/
Daniel CARO 氏 (Université de Caen Normandie)
Introduction to arithmetic D-modules (英語)
[ 講演概要 ]
In this talk, I will give a brief overview of the theory of D-arithmetic modules, initiated by P. Berthelot in the 90's. By replacing the analytic or complex algebraic varieties by algebraic varieties defined over a field of characteristic p>0, this corresponds to an arithmetic analogue of the usual theory of D-modules. This makes it possible to obtain categories of p-adic objects associated with varieties of characteristic p; these p-adic coefficients satisfying a six functors formalism as expected. Via the de Rham cohomology associated with the constant arithmetic D-module, we obtain a p-adic interpretation and the rationality of the Weil zeta function, an arithmetic avatar of the Riemann zeta function, as well as a p-adic analogue of the Riemann hypothesis.
[ 講演参考URL ]In this talk, I will give a brief overview of the theory of D-arithmetic modules, initiated by P. Berthelot in the 90's. By replacing the analytic or complex algebraic varieties by algebraic varieties defined over a field of characteristic p>0, this corresponds to an arithmetic analogue of the usual theory of D-modules. This makes it possible to obtain categories of p-adic objects associated with varieties of characteristic p; these p-adic coefficients satisfying a six functors formalism as expected. Via the de Rham cohomology associated with the constant arithmetic D-module, we obtain a p-adic interpretation and the rationality of the Weil zeta function, an arithmetic avatar of the Riemann zeta function, as well as a p-adic analogue of the Riemann hypothesis.
https://fj-lmi.cnrs.fr/seminars/
2024年09月11日(水)
13:30-14:30 数理科学研究科棟(駒場) 122号室
Çağrı SERT 氏 (Univeristy of Warwick)
Counting limit theorems for representations of Gromov-hyperbolic groups (英語)
https://fj-lmi.cnrs.fr/seminars/
Çağrı SERT 氏 (Univeristy of Warwick)
Counting limit theorems for representations of Gromov-hyperbolic groups (英語)
[ 講演概要 ]
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.
[ 講演参考URL ]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.
https://fj-lmi.cnrs.fr/seminars/
2024年06月10日(月)
13:30-14:30 数理科学研究科棟(駒場) 002号室
Sourav GHOSH 氏 (Ashoka University, India)
Affine Anosov representations
https://fj-lmi.cnrs.fr/seminars/
Sourav GHOSH 氏 (Ashoka University, India)
Affine Anosov representations
[ 講演概要 ]
In this survey talk I will give a brief overview of affine Anosov representations. These are appropriate analogues of Anosov representations inside affine Lie groups and are closely related with proper affine actions of hyperbolic groups.
[ 講演参考URL ]In this survey talk I will give a brief overview of affine Anosov representations. These are appropriate analogues of Anosov representations inside affine Lie groups and are closely related with proper affine actions of hyperbolic groups.
https://fj-lmi.cnrs.fr/seminars/
2024年04月24日(水)
15:00-16:00 数理科学研究科棟(駒場) 056号室
Laurent Di Menza 氏 (Université de Reims Champagne-Ardenne, CNRS)
Some aspects of Schrödinger models (英語)
https://fj-lmi.cnrs.fr/seminars/
Laurent Di Menza 氏 (Université de Reims Champagne-Ardenne, CNRS)
Some aspects of Schrödinger models (英語)
[ 講演概要 ]
In this talk, we focus on basic facts about the Schrödinger equation that arises in various physical contexts, from quantum mechanics to gravita-tional systems. This kind of equation has been intensively studied in the literature and many properties are known, either from a qualitative and quantitative point of view. The goal of this presentation is to give basic properties of solutions in different regimes. A particular effort will be paid for the numerical computation of solitons that consist in solutions that propagate with shape invariance.
[ 講演参考URL ]In this talk, we focus on basic facts about the Schrödinger equation that arises in various physical contexts, from quantum mechanics to gravita-tional systems. This kind of equation has been intensively studied in the literature and many properties are known, either from a qualitative and quantitative point of view. The goal of this presentation is to give basic properties of solutions in different regimes. A particular effort will be paid for the numerical computation of solitons that consist in solutions that propagate with shape invariance.
https://fj-lmi.cnrs.fr/seminars/
2024年04月10日(水)
16:00-17:00 数理科学研究科棟(駒場) 056号室
Séverin PHILIP 氏 (京都大学 数理解析研究所, RIMS, Kyoto University)
Galois outer representation and the problem of Oda
(英語)
https://fj-lmi.cnrs.fr/seminars/
Séverin PHILIP 氏 (京都大学 数理解析研究所, RIMS, Kyoto University)
Galois outer representation and the problem of Oda
(英語)
[ 講演概要 ]
Oda’s problem stems from considering the pro-l outer Galois actions on the moduli spaces of hyperbolic curves. These actions come from a generalization by Oda of the standard étale homotopy exact sequence for algebraic varieties over the rationals. We will introduce these geometric Galois actions and present some of the mathematics that they have stimulated over the past 30 years along with the classical problem of Oda. In the second and last part of this talk, we will see how a cyclic special loci version of this problem can be formulated and resolved in the case of simple cyclic groups using the maximal degeneration method of Ihara and Nakamura adapted to this setting.
[ 講演参考URL ]Oda’s problem stems from considering the pro-l outer Galois actions on the moduli spaces of hyperbolic curves. These actions come from a generalization by Oda of the standard étale homotopy exact sequence for algebraic varieties over the rationals. We will introduce these geometric Galois actions and present some of the mathematics that they have stimulated over the past 30 years along with the classical problem of Oda. In the second and last part of this talk, we will see how a cyclic special loci version of this problem can be formulated and resolved in the case of simple cyclic groups using the maximal degeneration method of Ihara and Nakamura adapted to this setting.
https://fj-lmi.cnrs.fr/seminars/
2024年03月11日(月)
13:30-14:30 数理科学研究科棟(駒場) 117号室
Florian SALIN 氏 (Université de Lyon - Tohoku University)
Fractional Nonlinear Diffusion Equation: Numerical Analysis and Large-time Behavior. (英語)
https://fj-lmi.cnrs.fr/seminars/
Florian SALIN 氏 (Université de Lyon - Tohoku University)
Fractional Nonlinear Diffusion Equation: Numerical Analysis and Large-time Behavior. (英語)
[ 講演概要 ]
This talk will discuss a fractional nonlinear diffusion equation on bounded domains. This equation arises by combining fractional (in space) diffusion, with a nonlinearity of porous medium or fast diffusion type. It is known that, in the porous medium case, the energy of the solutions to this equation decays algebraically, and in the fast diffusion case, solutions extinct in finite time. Based on these estimates, we will study the fine large-time asymptotic behavior of the solutions. In particular, we will show that the solutions approach separate variable solutions as the time converges to infinity in the porous medium case, or as it converges to the extinction time in the fast diffusion case. However, the extinction time is not known analytically, and to compute it, we will introduce a numerical scheme that satisfies the same decay estimates as the continuous equation.
[ 講演参考URL ]This talk will discuss a fractional nonlinear diffusion equation on bounded domains. This equation arises by combining fractional (in space) diffusion, with a nonlinearity of porous medium or fast diffusion type. It is known that, in the porous medium case, the energy of the solutions to this equation decays algebraically, and in the fast diffusion case, solutions extinct in finite time. Based on these estimates, we will study the fine large-time asymptotic behavior of the solutions. In particular, we will show that the solutions approach separate variable solutions as the time converges to infinity in the porous medium case, or as it converges to the extinction time in the fast diffusion case. However, the extinction time is not known analytically, and to compute it, we will introduce a numerical scheme that satisfies the same decay estimates as the continuous equation.
https://fj-lmi.cnrs.fr/seminars/
2024年01月30日(火)
16:30-17:30 数理科学研究科棟(駒場) 号室
Danielle HILHORST 氏 (CNRS, Université de Paris-Saclay, France)
Convergence of solutions of a one-phase Stefan problem with Neumann boundary data to a self-similar profile. (英語)
https://fj-lmi.cnrs.fr/seminars/
Danielle HILHORST 氏 (CNRS, Université de Paris-Saclay, France)
Convergence of solutions of a one-phase Stefan problem with Neumann boundary data to a self-similar profile. (英語)
[ 講演概要 ]
We study a one-dimensional one-phase Stefan problem with a Neumann boundary condition on the fixed part of the boundary.
We construct a unique self-similar solution and show that for a large class of initial data, the solution of the time evolution problem
converges to this self-similar solution as time tends to infinity. Similar results were already obtained by Bouguezzi, Hilhorst,
Miyamoto, and Scheid in the case of Dirichlet data on the fixed boundary. However, they had to show that the space derivative
of the solution uniformly converges to its limit. Here, our proof requires less regularity, which should make our arguments easier
to adapt to different settings.
This is a joint work with Sabrina Roscani and Piotr Rybka.
[ 講演参考URL ]We study a one-dimensional one-phase Stefan problem with a Neumann boundary condition on the fixed part of the boundary.
We construct a unique self-similar solution and show that for a large class of initial data, the solution of the time evolution problem
converges to this self-similar solution as time tends to infinity. Similar results were already obtained by Bouguezzi, Hilhorst,
Miyamoto, and Scheid in the case of Dirichlet data on the fixed boundary. However, they had to show that the space derivative
of the solution uniformly converges to its limit. Here, our proof requires less regularity, which should make our arguments easier
to adapt to different settings.
This is a joint work with Sabrina Roscani and Piotr Rybka.
https://fj-lmi.cnrs.fr/seminars/
2024年01月23日(火)
13:30-14:40 数理科学研究科棟(駒場) 118号室
Antoine DIEZ 氏 (京都大学, Kyoto University, ASHBi)
Particle systems with geometrical constraints and applications (英語)
https://fj-lmi.cnrs.fr/seminars/
Antoine DIEZ 氏 (京都大学, Kyoto University, ASHBi)
Particle systems with geometrical constraints and applications (英語)
[ 講演概要 ]
Since the pioneering work of Boltzmann, statistical physics has moti-vated the mathematical study or large systems of interacting particles, especially at the interface between stochastic analysis and PDE. More recently, there has been a surge of interest to consider applications to life sciences, where particles can be seen as convenient modeling entities to represent e.g. cell aggregates, bacterial swarms or animal societies. An important question in this context is the link between the microscopic agent-based description and the macroscopic continuum PDE description. Unlike physical systems which generally obey conservation laws, biological systems are rather subjects to constraints which are more geometrical in nature: volume constraints, shape or internal structure for instance. This poses a number of challenges on the modeling, analytical and numerical aspects. In this talk, I will first review earlier works on the study of particle systems with geometrical constraints. Then I will introduce a new framework, based on optimal transport theory, to model particles with arbitrary shapes and deformability properties. I will discuss potential applications in biology and compare this novel approach to other more classical methods.
[ 講演参考URL ]Since the pioneering work of Boltzmann, statistical physics has moti-vated the mathematical study or large systems of interacting particles, especially at the interface between stochastic analysis and PDE. More recently, there has been a surge of interest to consider applications to life sciences, where particles can be seen as convenient modeling entities to represent e.g. cell aggregates, bacterial swarms or animal societies. An important question in this context is the link between the microscopic agent-based description and the macroscopic continuum PDE description. Unlike physical systems which generally obey conservation laws, biological systems are rather subjects to constraints which are more geometrical in nature: volume constraints, shape or internal structure for instance. This poses a number of challenges on the modeling, analytical and numerical aspects. In this talk, I will first review earlier works on the study of particle systems with geometrical constraints. Then I will introduce a new framework, based on optimal transport theory, to model particles with arbitrary shapes and deformability properties. I will discuss potential applications in biology and compare this novel approach to other more classical methods.
https://fj-lmi.cnrs.fr/seminars/
2023年12月04日(月)
14:00- 数理科学研究科棟(駒場) 056号室
Philippe G. LEFLOCH 氏 (Sorbonne University & CNRS)
An introduction to Einstein constraints and the seed-to-solution method
https://fj-lmi.cnrs.fr/seminars/
Philippe G. LEFLOCH 氏 (Sorbonne University & CNRS)
An introduction to Einstein constraints and the seed-to-solution method
[ 講演概要 ]
I will present an introduction to the constraint equations associated with Einstein’s field equations of general relativity, and to recent developments based on the seed-to-solution method developed in collaboration with The-Cang Nguyen (Montpellier) and Bruno Le Floch (LPTHE, Sorbonne).
[ 講演参考URL ]I will present an introduction to the constraint equations associated with Einstein’s field equations of general relativity, and to recent developments based on the seed-to-solution method developed in collaboration with The-Cang Nguyen (Montpellier) and Bruno Le Floch (LPTHE, Sorbonne).
https://fj-lmi.cnrs.fr/seminars/
2023年11月28日(火)
16:00- 数理科学研究科棟(駒場) 117号室
Maud DELATTRE 氏 (Université Paris-Saclay, INRAE)
Some contributions on variable selection in nonlinear mixed-effects models
https://fj-lmi.cnrs.fr/seminars/
Maud DELATTRE 氏 (Université Paris-Saclay, INRAE)
Some contributions on variable selection in nonlinear mixed-effects models
[ 講演概要 ]
In the first part of this presentation, we will introduce the general formalism of nonlinear mixed effects models (NLMEM) that are specifically designed models to describe dynamic phenomena from repeated data on several subjects. In the second part, we will focus on specific variable selection technics for NLMEM through two contributions. In the first one, we will discuss the proper definition and use of the Bayesian information criterion (BIC) for variable selection in a low dimensional setting. High dimensional variable selection is the subject of the second contribution.
References
[1] Delattre, M., Lavielle, M. and Poursat, M.A. (2014) A note on BIC in mixed effects models, Electronic Journal of Statistics 8(1) p. 456-475.
[2] Delattre, M. and Poursat, M.A. (2020) An iterative algorithm for joint covariate and random effect selection in mixed effects models., The International Journal of Biostatistics 16(2), 20190082.
[3] Naveau, M., Kon Kam King, G., Rincent, R., Sansonnet, L. and Delattre, M. Bayesian high dimensional covariate selection in non-linear mixed-effects models using the SAEM algorithm. hal-03685060.
[ 講演参考URL ]In the first part of this presentation, we will introduce the general formalism of nonlinear mixed effects models (NLMEM) that are specifically designed models to describe dynamic phenomena from repeated data on several subjects. In the second part, we will focus on specific variable selection technics for NLMEM through two contributions. In the first one, we will discuss the proper definition and use of the Bayesian information criterion (BIC) for variable selection in a low dimensional setting. High dimensional variable selection is the subject of the second contribution.
References
[1] Delattre, M., Lavielle, M. and Poursat, M.A. (2014) A note on BIC in mixed effects models, Electronic Journal of Statistics 8(1) p. 456-475.
[2] Delattre, M. and Poursat, M.A. (2020) An iterative algorithm for joint covariate and random effect selection in mixed effects models., The International Journal of Biostatistics 16(2), 20190082.
[3] Naveau, M., Kon Kam King, G., Rincent, R., Sansonnet, L. and Delattre, M. Bayesian high dimensional covariate selection in non-linear mixed-effects models using the SAEM algorithm. hal-03685060.
https://fj-lmi.cnrs.fr/seminars/
2023年11月24日(金)
14:00-14:40 数理科学研究科棟(駒場) 117号室
Gwénaël MASSUYEAU 氏 (Université de Bourgogne & CNRS)
Surgery equivalence relations on 3-manifolds (English)
https://fj-lmi.cnrs.fr/seminars/
Gwénaël MASSUYEAU 氏 (Université de Bourgogne & CNRS)
Surgery equivalence relations on 3-manifolds (English)
[ 講演概要 ]
By some classical results in low-dimensional topology, any two 3-manifolds (with the “same” boundaries) are related one to the other by surgery operations. In this survey talk, we shall review this basic fact and, next, by restricting the type of surgeries, we shall consider several families of non-trivial equivalence relations on the set of (homeomorphism classes of) 3-manifolds. Those “surgery equivalence relations” are defined in terms of filtrations of the mapping class groups of surfaces, and their characterization / classification involves the notion of “finite-type invariant” which arises in quantum topology.
[ 講演参考URL ]By some classical results in low-dimensional topology, any two 3-manifolds (with the “same” boundaries) are related one to the other by surgery operations. In this survey talk, we shall review this basic fact and, next, by restricting the type of surgeries, we shall consider several families of non-trivial equivalence relations on the set of (homeomorphism classes of) 3-manifolds. Those “surgery equivalence relations” are defined in terms of filtrations of the mapping class groups of surfaces, and their characterization / classification involves the notion of “finite-type invariant” which arises in quantum topology.
https://fj-lmi.cnrs.fr/seminars/
