We are interested in a system of particles in singular mean-field interaction and wish to prove that, as the number of particles goes to infinity, two given particles within that system become « more and more » independent, a phenomenon known as propagation of chaos. The interaction we will focus on comes from the Biot-Savart kernel, for which the nonlinear limit of the particle system satisfies the vorticity equation, arising from the 2D incompressible Navier-Stokes system. We build upon a recent work of P.-E. Jabin and Z. Wang to obtain a uniform in time convergence. The approach consists in computing the time evolution of the relative entropy of the joint law of the particle system with respect to the nonlinear limit. We prove time-uniform bounds on the limit, as well as a logarithmic Sobolev inequality. From the latter, the Fisher information appearing in the entropy dissipation yields a control on the relative entropy itself, inducing the time uniformity. This is joint work with A. Guillin and P. Monmarché.

We are going present a multi-scale analysis to derive log-Sobolev inequalities for interacting particle systems. This leads to a generalised Bakry-Emery criterion which can be applied to non-convex potentials. The approach relies on a Hamilton-Jacobi equation know as Polchinski equation. If time allows, we will explain how this multi-scale criterion allows to build Lipschitz transport maps. This talk is based on the survey arXiv:2307.07619 in collaboration with R. Bauerschmidt and B. Dagallier.

In this talk I will present some general strategies for proving (possibly constructive) rate of convergence in the longtime asymptotic for solutions to linear evolution equations. I will next explain how to implement these strategy in the case of the kinetic Fokker-Planck equation for several geometries (torus, whole space with confinement force, bounded domain with reflection condition).

In recent works it has been demonstrated that using an appropriate rescaling, linear kinetic equations with heavy tailed equilibria give rise to a scalar fractional diffusion equation. In this talk an extension of this is presented, where the linear kinetic equations under consideration, not only conserves mass, but also momentum and energy. In the limit, fractional diffusion equations are obtained for the energy and the mass, while the equation for the momentum is trivial. The methods of proof presented rely on spectral analysis combined with energy estimates. It is constructive and provides explicit convergence rates. This is work in progress together with É. Bouin and C. Mouhot.

I discuss improved lattice models in three dimensions. Improved means that either one or two parameters of the model are tuned such that the leading or the leading and the next to leading correction to scaling have, at least approximately, a vanishing amplitude. This is achieved by using a finite size scaling analysis of dimensionless quantities. Based on these results, accurate estimates of universal quantities such as critical exponents are obtained. I summarize results that have been obtained for the Ising, the XY, the Heisenberg and the cubic universality classes and compare them with those obtained by other methods, in particular precise estimates obtained recently by using the conformal bootstrap method. Pour être informé des prochains séminaires vous pouvez vous abonner à la liste de diffusion en écrivant un mail à sympa@listes.math.cnrs.fr avec comme sujet: « subscribe seminaire_physique PRENOM NOM »(indiquez vos propres prénom et nom) et laissez le corps du message vide.

We will consider perturbations of 2D CFTs by multiple relevant operators. The massive phases of such perturbations can be labeled by conformal boundary conditions. Cardy’s variational ansatz approximates the vacuum state of the perturbed theory by a smeared conformal boundary state. In this talk we will discuss the limitations and propose generalisations of this ansatz using both analytic and numerical insights based on TCSA. In particular we analyse the stability of Cardy’s ansatz states with respect to boundary relevant perturbations using  bulk-boundary OPE coefficients. We show that certain transitions  between the massive phases arise from a pair of boundary RG flows.  The RG flows start from the conformal boundary on the transition surface and end on those that lie on the two sides of it. As an example we work out the details of the phase diagram for the Ising field theory and for the tricritical Ising model  perturbed by the leading thermal and magnetic fields. Based on arXiv:2306.13719. Pour être informé des prochains séminaires vous pouvez vous abonner à la liste de diffusion en écrivant un mail à sympa@listes.math.cnrs.fr avec comme sujet: « subscribe seminaire_physique PRENOM NOM »(indiquez vos propres prénom et nom) et laissez le corps du message vide.

Probability and analysis informal seminarOne way of proving probabilistic functional inequalities (concentration inequalities, logarithmic Sobolev inequalities…) is to use a change of variables, to transfer them from a simple reference measure (typically, Gaussian) to more general settings. One example of this is the Caffarelli contraction theorem, which states that uniformly log-concave measures can be realized as images of standard Gaussian measures by globally lipschitz maps, using the L2 optimal transport map. One open problem in this direction is to find an analogue of Caffarelli’s theorem in the Riemannian setting.In this talk, I will present a stochastic construction of non-optimal maps, due to Kim and Milman, and Lipschitz estimates in various settings, including certain measures on Riemannian manifolds. Joint work with Dan Mikulincer and Yair Shenfeld. ========Pour être informé des prochains séminaires vous pouvez vous abonner à la liste de diffusion en écrivant un mail à sympa@listes.math.cnrs.fr avec comme sujet: « subscribe seminaire_mathematique PRENOM NOM »(indiquez vos propres prénom et nom) et laissez le corps du message vide.

We discuss general properties of perturbative RG flows in AdS with a focus on the treatment of boundary conditions and infrared divergences. In contrast with flat-space boundary QFT, general covariance in AdS implies the absence of independent boundary flows. We illustrate how boundary correlation functions remain conformally covariant even if the bulk QFT has a scale. We apply our general discussion to the RG flow between consecutive unitary diagonal minimal models which is triggered by the φ(1,3) operator. For these theories we conjecture a flow diagram whose form is significantly simpler than that in flat-space boundary QFT. Pour être informé des prochains séminaires vous pouvez vous abonner à la liste de diffusion en écrivant un mail à sympa@listes.math.cnrs.fr avec comme sujet: « subscribe seminaire_physique PRENOM NOM »(indiquez vos propres prénom et nom) et laissez le corps du message vide.

Let G be a simply-connected complex simple algebraic group and let C be a smooth projective curve of any genus. Then, the moduli space of semistable G-bundles on C admits so called determinant line bundles. E. Verlinde conjectured a remarkable formula to calculate the dimension of the space of generalized theta functions, which is by definition the space of global sections of a determinant line bundle. This space is also identified with the space of conformal blocks arising in Conformal Field Theory, which is by definition the space of coinvariants in integrable highest weight modules of affine Kac-Moody Lie algebras. Various works notably by Tsuchiya-Ueno-Yamada, Kumar-Narasimhan-Ramanathan, Faltings, Beauville-Laszlo, Sorger and Teleman culminated into a proof of the Verlinde formula. The main aim of this talk is to give a basic outline of the proof of this formula derived from the Propogation of Vacua and the Factorization Theorem among others. The proof requires techniques from algebraic geometry, geometric invariant theory, representation theory of affine Kac-Moody Lie algebras, topology, and Lie algebra cohomology. Some basic knowledge of algebraic geometry and representation theory of semisimple Lie algebras will be helpful; but not required. This lecture should be suitable for any one interested in interaction between algebraic geometry, representation theory, topology and mathematical physics. Pour être informé des prochains séminaires vous pouvez vous abonner à la liste de diffusion en écrivant un mail à sympa@listes.math.cnrs.fr avec comme sujet: « subscribe seminaire_mathematique PRENOM NOM »(indiquez vos propres prénom et nom) et laissez le corps du message vide. 

The presence of nearby complex conformal field theories (CCFTs) hidden in the complex plane of the tuning parameter was recently proposed as an elegant explanation for the ubiquity of « weakly first-order » transitions in condensed matter and high-energy systems. Recently, we have numerically confirmed the presence of such a CCFT in a loop model which derives from a high-temperature formulation of the O(n) model. Surprisingly, we found that the CCFT only survives until n=12.34, beyond which the transfer matrix acquires a gap. In this talk, I will discuss ongoing work in trying to explain this loss of complex conformality at large n, using a mapping to a hard hexagon model for n going to infinity. I will also discuss the connection between the original O(n) model and its loop version and the consequences for CCFTs in these models. Pour être informé des prochains séminaires vous pouvez vous abonner à la liste de diffusion en écrivant un mail à sympa@listes.math.cnrs.fr avec comme sujet: « subscribe seminaire_physique PRENOM NOM »(indiquez vos propres prénom et nom) et laissez le corps du message vide.

Probability and analysis informal seminarWe study the limit in low intensity of Poisson–Voronoi tessellations in hyperbolic spaces. In contrast to the Euclidean setting, a limiting non-trivial ideal tessellation appears as the intensity tends to 0. The tessellation obtained is a natural Möbius-invariant decomposition of the hyperbolic space into countably many infinite convex polytopes, each with a unique end. We study its basic properties, in particular the geometric features of its cells.Based on joint works with Matteo d’Achille, Nathanel Enriquez, Russell Lyons and Meltem Unel. ========Pour être informé des prochains séminaires vous pouvez vous abonner à la liste de diffusion en écrivant un mail à sympa@listes.math.cnrs.fr avec comme sujet: « subscribe seminaire_mathematique PRENOM NOM »(indiquez vos propres prénom et nom) et laissez le corps du message vide.

In 2010, de Cataldo-Miglorini used generic flags to compute the perverse filtration on the cohomology of an affine variety with values in a constructible sheaf. In this talk, I shall introduce the Brylinski-Radon transformation, discuss its properties and derive consequences for the perverse filtration. We shall also discuss some arithmetic applications of our results. This is joint work with Ankit Rai.  Pour être informé des prochains séminaires vous pouvez vous abonner à la liste de diffusion en écrivant un mail à sympa@listes.math.cnrs.fr avec comme sujet: « subscribe seminaire_mathematique PRENOM NOM »(indiquez vos propres prénom et nom) et laissez le corps du message vide.