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Documents : Multi angle  Conférences Vidéo | enregistrements trouvés : 200

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Multi angle  (In)efficiency in mean field games Cardaliaguet, Pierre (Auteur de la Conférence) | CIRM (Editeur )

Mean field games (MFG) are dynamic games with infinitely many infinitesimal agents. In this joint work with Catherine Rainer (U. Brest), we study the efficiency of Nash MFG equilibria: Namely, we compare the social cost of a MFG equilibrium with the minimal cost a global planner can achieve. We find a structure condition on the game under which there exists efficient MFG equilibria and, in case this condition is not fulfilled, quantify how inefficient MFG equilibria are.
Mean field games (MFG) are dynamic games with infinitely many infinitesimal agents. In this joint work with Catherine Rainer (U. Brest), we study the efficiency of Nash MFG equilibria: Namely, we compare the social cost of a MFG equilibrium with the minimal cost a global planner can achieve. We find a structure condition on the game under which there exists efficient MFG equilibria and, in case this condition is not fulfilled, quantify how ...

35Q91

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Multi angle  $L^2$ Hypocoercivity Dolbeault, Jean (Auteur de la Conférence) | CIRM (Editeur )

The purpose of the $L^2$ hypocoercivity method is to obtain rates for solutions of linear kinetic equations without regularizing effects, in asymptotic regimes. Initially intended for systems with confinement in position space and simple local equilibria, the method has been extended to various local equilibria in velocities and non-compact situations in positions. It is also flexible enough to include non-local transport terms associated with Poisson coupling. The lecture will be devoted to a review of some recent results.
The purpose of the $L^2$ hypocoercivity method is to obtain rates for solutions of linear kinetic equations without regularizing effects, in asymptotic regimes. Initially intended for systems with confinement in position space and simple local equilibria, the method has been extended to various local equilibria in velocities and non-compact situations in positions. It is also flexible enough to include non-local transport terms associated with ...

82C40

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Multi angle  $L^p$-theory for Schrödinger systems Rhandi, Abdelaziz (Auteur de la Conférence) | CIRM (Editeur )

In this talk we study for $p\in \left ( 1,\infty \right )$ the $L^{p}$-realization of the vector-valued Schrödinger operator $\mathcal{L}u:= div\left ( Q\triangledown u \right )+Vu$. Using a noncommutative version of the Dore-Venni theorem due to Monniaux and Prüss, and a perturbation theorem by Okazawa, we prove that $L^{p}$, the $L^{p}$-realization of $\mathcal{L}$, defined on the intersection of the natural domains of the differential and multiplication operators which form $\mathcal{L}$, generates a strongly continuous contraction semigroup on $L^{p}\left ( \mathbb{R}^{d} ;\mathbb{C}^{m}\right )$. We also study additional properties of the semigroup such as positivity, ultracontractivity, Gaussian estimates and compactness of the resolvent. We end the talk by giving some generalizations obtained recently and several examples.
In this talk we study for $p\in \left ( 1,\infty \right )$ the $L^{p}$-realization of the vector-valued Schrödinger operator $\mathcal{L}u:= div\left ( Q\triangledown u \right )+Vu$. Using a noncommutative version of the Dore-Venni theorem due to Monniaux and Prüss, and a perturbation theorem by Okazawa, we prove that $L^{p}$, the $L^{p}$-realization of $\mathcal{L}$, defined on the intersection of the natural domains of the differential and ...

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Multi angle  $T$-structures from categorical actions Koppensteiner, Clemens (Auteur de la Conférence) | CIRM (Editeur )

$T$-structures on derived categories of coherent sheaves are an important tool to encode both representation-theoretic and geometric information. Unfortunately there are only a limited amount of tools available for the constructions of such $t$-structures. We show how certain geometric/categorical quantum affine algebra actions naturally induce $t$-structures on the categories underlying the action. In particular we recover the categories of exotic sheaves of Bezrukavnikov and Mirkovic.
This is joint work with Sabin Cautis.
$T$-structures on derived categories of coherent sheaves are an important tool to encode both representation-theoretic and geometric information. Unfortunately there are only a limited amount of tools available for the constructions of such $t$-structures. We show how certain geometric/categorical quantum affine algebra actions naturally induce $t$-structures on the categories underlying the action. In particular we recover the categories of ...

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Multi angle  A brief introduction to concentration inequalities Chazottes, Jean-René (Auteur de la Conférence) | CIRM (Editeur )

$Let (X,T)$ be a dynamical system preserving a probability measure $\mu$. A concentration inequality quantifies how small is the probability for $F(x,Tx,\ldots,T^{n-1}x)$ to deviate from $\int F(x,Tx,\ldots,T^{n-1}x) \mathrm{d}\mu(x)$ by an given amount $u$, where $F:X^n\to\mathbb{R}$ is supposed to be separately Lipschitz. The bound on that probability involves a constant $C$ depending only on the dynamical system (thus independent of $n$), and $\sum_{i=0}^{n-1} \mathrm{Lip}_i(F)^2$. In the best situation, the bound is $\exp(-C u^2/\sum_{i=0}^{n-1} \mathrm{Lip}_i(F)^2)$.
After explaining how to get such a bound for independent random variables, I will show how to prove it for a Gibbs measure on a shift of finite type with a Lipschitz potential, and present examples of functions $F$ to which one can apply the inequality. Finally, I will survey some results obtained for nonuniformly hyperbolic systems modeled by Young towers.
$Let (X,T)$ be a dynamical system preserving a probability measure $\mu$. A concentration inequality quantifies how small is the probability for $F(x,Tx,\ldots,T^{n-1}x)$ to deviate from $\int F(x,Tx,\ldots,T^{n-1}x) \mathrm{d}\mu(x)$ by an given amount $u$, where $F:X^n\to\mathbb{R}$ is supposed to be separately Lipschitz. The bound on that probability involves a constant $C$ depending only on the dynamical system (thus independent of $n$), ...

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Multi angle  A critical Poincaré-Sobolev inequality van den Bosch, Hanne (Auteur de la Conférence) | CIRM (Editeur )

We study a specific Poincaré-Sobolev inequality in bounded domains, that has recently been used to prove a semi-classical bound on the kinetic energy of fermionic many-body states. The corresponding inequality in the entire space is precisely scale invariant and this gives rise to an interesting phenomenon. Optimizers exist for some (most ?) domains and do not exist for some other domains, at least for the isosceles triangle in two dimensions. In this talk, I will discuss bounds on the constant in the inequality and the proofs of existence and non-existence.
This is joint work with Rafael Benguria and Cristobal Vallejos (PUC, Chile)
We study a specific Poincaré-Sobolev inequality in bounded domains, that has recently been used to prove a semi-classical bound on the kinetic energy of fermionic many-body states. The corresponding inequality in the entire space is precisely scale invariant and this gives rise to an interesting phenomenon. Optimizers exist for some (most ?) domains and do not exist for some other domains, at least for the isosceles triangle in two dimensions. ...

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Multi angle  A geometric $R$-matrix for the Hilbert scheme of points on a general surface Arbesfeld, Noah (Auteur de la Conférence) | CIRM (Editeur )

We explain how to use a Virasoro algebra to construct a solution to the Yang-Baxter equation acting in the tensor square of the cohomology of the Hilbert scheme of points on a generalsurface $S$. In the special case where the surface $S$ is $C^2$, the construction appears in work of Maulik and Okounkov on the quantum cohomology of symplectic resolutions and recovers their $R$-matrix constructed using stable envelopes.

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Multi angle  A sheaf theoretic approach towards calculating simple characters of algebraic groups Fiebig, Peter (Auteur de la Conférence) | CIRM (Editeur )

Since Geordie Williamson showed that the exceptional primes for an algebraic group grow at least exponentially with the rank, the problem of calculating simple characters seems to be less approachable than ever before. In the talk I will give a short overview on recent results on simple characters, and I want to introduce a category that is rather elementary to define and still encodes the whole character problem.
This category is the result of joint work with Martina Lanini.
Since Geordie Williamson showed that the exceptional primes for an algebraic group grow at least exponentially with the rank, the problem of calculating simple characters seems to be less approachable than ever before. In the talk I will give a short overview on recent results on simple characters, and I want to introduce a category that is rather elementary to define and still encodes the whole character problem.
This category is the result of ...

17B15

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Multi angle  A statistical physics approach to the sine beta process Maïda, Mylène (Auteur de la Conférence) | CIRM (Editeur )

The universality properties of the Sine process (corresponding to inverse temperature beta equal to 2) are now well known. More generally, a family of point processes have been introduced by Valko and Virag and shown to be the bulk limit of Gaussian beta ensembles, for any positive beta. They are defined through a one-parameter family of SDEs coupled by a two-dimensional Brownian motion (or more recently as the spectrum of a random operator). Through these descriptions, some properties have been derived by Holcomb, Paquette, Valko, Virag and others but there is still much to understand.
In a work with David Dereudre, Adrien Hardy (Université de Lille) and Thomas Leblé (Courant Institute, New York), we use tools from classical statistical mechanics based on DLR equations to give a completely different description of the Sine beta process and derive some properties, such as rigidity and tolerance.
The universality properties of the Sine process (corresponding to inverse temperature beta equal to 2) are now well known. More generally, a family of point processes have been introduced by Valko and Virag and shown to be the bulk limit of Gaussian beta ensembles, for any positive beta. They are defined through a one-parameter family of SDEs coupled by a two-dimensional Brownian motion (or more recently as the spectrum of a random operator). ...

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Multi angle  A tale of Pfaffian persistence tails told by a Bonnet-Painlevé VI transcendent Dornic, Ivan (Auteur de la Conférence) | CIRM (Editeur )

We identify the persistence probability for the zero-temperature non-equilibrium Glauber dynamics of the half-space Ising chain as a particular Painlevé VI transcendent, with monodromy exponents (1/2,1/2,0,0). Among other things, this characterization a la Tracy-Widom permits to relate our specific Bonnet-Painlevé VI to the one found by Jimbo & Miwa and characterizing the diagonal correlation functions for the planar static Ising model. In particular, in terms of the standard critical exponents eta=1/4 and beta=1/8 for the latter, this implies that the probability that the limiting Gaussian real Kac's polynomial has no real root decays with an exponent 4(eta+beta)=3/4.
We identify the persistence probability for the zero-temperature non-equilibrium Glauber dynamics of the half-space Ising chain as a particular Painlevé VI transcendent, with monodromy exponents (1/2,1/2,0,0). Among other things, this characterization a la Tracy-Widom permits to relate our specific Bonnet-Painlevé VI to the one found by Jimbo & Miwa and characterizing the diagonal correlation functions for the planar static Ising model. In ...

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Multi angle  Adding small viscosity to hyperbolic (stochastic) conservation laws Boritchev, Alexandre (Auteur de la Conférence) | CIRM (Editeur )

The mechanism responsible for blow-up is well-understood for many hyperbolic conservation laws. Indeed, for a whole class of problems including the Burgers equation and many aggregation-diffusion equations such as the 1D parabolic-elliptic Keller-Segel system, the time and nature of the blow-up can be estimated by ODE arguments. It is, however, a much more delicate question to understand the small-scale behaviour of the viscous layers appearing in (classic or fractional) parabolic regularisations of these conservation laws.
Here we give sharp estimates for Sobolev norms and for a class of small-scale quantities such as increments and energy spectrum (which are relevant for the theory of turbulence), for solutions of these conservation laws. Moreover, many of our results can be generalised for perturbations of the viscous conservation laws by random additive noise, and some of them admit a simpler formulation in this case. To our best knowledge, these are the only sharp results of this type for small-scale behaviour of solutions of nonlinear PDEs.
The work on the aggregation-diffusion equations is an ongoing collaboration with Piotr Biler and Grzegorz Karch (Wroclaw) and Philippe Laurençot (Toulouse).
The mechanism responsible for blow-up is well-understood for many hyperbolic conservation laws. Indeed, for a whole class of problems including the Burgers equation and many aggregation-diffusion equations such as the 1D parabolic-elliptic Keller-Segel system, the time and nature of the blow-up can be estimated by ODE arguments. It is, however, a much more delicate question to understand the small-scale behaviour of the viscous layers ...

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Multi angle  Additive combinatorics methods in fractal geometry - lecture 1 Shmerkin, Pablo (Auteur de la Conférence) | CIRM (Editeur )

In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for explicit values of the parameter.
In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for ...

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Multi angle  Additive combinatorics methods in fractal geometry - lecture 1 Varju, Peter (Auteur de la Conférence) | CIRM (Editeur )

In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for explicit values of the parameter.
In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for ...

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Multi angle  Additive combinatorics methods in fractal geometry - lecture 2 Shmerkin, Pablo (Auteur de la Conférence) | CIRM (Editeur )

In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for explicit values of the parameter.
In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for ...

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Multi angle  Additive combinatorics methods in fractal geometry - lecture 2 Varju, Peter (Auteur de la Conférence) | CIRM (Editeur )

In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for explicit values of the parameter.
In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for ...

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Multi angle  Additive combinatorics methods in fractal geometry - lecture 3 Shmerkin, Pablo (Auteur de la Conférence) | CIRM (Editeur )

In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for explicit values of the parameter.
In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for ...

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Multi angle  Additive combinatorics methods in fractal geometry - lecture 3 Varju, Peter (Auteur de la Conférence) | CIRM (Editeur )

In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for explicit values of the parameter.
In the last few years ideas from additive combinatorics were applied to problems in fractal geometry and led to progress on some classical problems, particularly on the smoothness of Bernoulli convolutions and other self-similar measures. We will introduce some of these tools from additive combinatorics and present some of the main applications, including the smoothness of Bernoulli convolutions outside of a small set of exceptions, and for ...

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Multi angle  Affine Springer fibers and G1T modules Vasserot, Eric (Auteur de la Conférence) | CIRM (Editeur )

I will explain a relation between the center of the category of G1T modules and the cohomology of affine Springer fibers, and I'll discuss several related conjectures.
This is a joint work with P. Shan.

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Multi angle  ALC manifolds with exceptional holonomy Foscolo, Lorenzo (Auteur de la Conférence) | CIRM (Editeur )

We will describe the construction of complete non-compact Ricci-flat manifolds of dimension 7 and 8 with holonomy $G_{2}$ and Spin(7) respectively. The examples we consider all have non-maximal volume growth and an asymptotic geometry, so-called ALC geometry, that generalises to higher dimension the asymptotic geometry of 4-dimensional ALF hyperkähler metrics. The interest in these metrics is motivated by the study of codimension 1 collapse of compact manifolds with exceptional holonomy. The constructions we will describe are based on the study of adiabatic limits of ALC metrics on principal Seifert circle fibrations over asymptotically conical orbifolds, cohomogeneity one techniques and the desingularisation of ALC spaces with isolated conical singularities. The talk is partially based on joint work with Mark Haskins and Johannes Nordstrm.
We will describe the construction of complete non-compact Ricci-flat manifolds of dimension 7 and 8 with holonomy $G_{2}$ and Spin(7) respectively. The examples we consider all have non-maximal volume growth and an asymptotic geometry, so-called ALC geometry, that generalises to higher dimension the asymptotic geometry of 4-dimensional ALF hyperkähler metrics. The interest in these metrics is motivated by the study of codimension 1 collapse of ...

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Multi angle  Algebraic and arithmetic aspects of twistor spaces Huybrechts, Daniel (Auteur de la Conférence) | CIRM (Editeur )

I will recall the well-known notion of twistor spaces for K3 surfaces (and Hyperkähler manifolds) and discuss some natural questions relating to the algebraic and arithmetic geometry of their fibres.

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