Centre de Physique Théorique


Novembre 2017

Du 30 octobre au 3 novembre, CIRM, Luminy

Collisionless Boltzmann (Vlasov) Equation and Modeling of Self-Gravitating Systems and Plasmas

Conférence internationale co-organisée par R. Triay (CPT)

The modelling of the matter interactions at long range is a fertile problem for Mathematics, a major issue in Physics and a challenge for Analysis and Numerical Simulations. The aim of this meeting is to conjugate all these aspects, with a special attention to the simulations, and try to infuse a stimulating working atmosphere, such as in a workshop, with few key lectures (part of these will be chosen when finalizing the program).

Vendredi 3 novembre 14:00-15:00, Amphi 5 du CPT

Patterns of New Physics in b→sℓ+ℓ− transitions in the light of recent data

Bernat Capdevilla (IFES, Barcellona)

In the Standard Model (SM), the rare transitions where a bottom quark decays into a strange quark and a pair of light leptons exhibit a potential sensitivity to physics beyond the SM. In addition, the SM embeds Lepton Flavour Universality (LFU), leading to almost identical probabilities for muon and electron modes. The LHCb collaboration discovered a set of deviations from the SM expectations in decays to muons and also in ratios assessing LFU. Other experiments (Belle, ATLAS, CMS) found consistent measurements, albeit with large error bars. To assess the extend of potential New Physics effects, we perform a global fit to all available b→sℓ+ℓ− data (l = e,μ) in a model-independent way. In this seminar, I will introduce to you the techniques used for the computation of the relevant observables in b→sℓ+ℓ− transitions, paying special attention to the treatment of hadronic uncertainties, present the latest results of our global analysis and discuss the opportunities that new observables testing LFU violation can provide.

Vendredi 10 novembre 11:00-12:00, Amphi 5 du CPT

Moving frames on Finsler surfaces

Vasile Sorin SABAU

In this talk we will use the method of moving frames for describing the existence and construction of a Finsler structure of constant flag curvature $K=1$ as well as Finsler structure with vanishing Landsberg curvature. The method is basically based on the Cartan double fibration and was developed initially by R. Bryant. It is remarkable that Riemannian surfaces with special geodesic properties actually induce Finsler metrics with prescribed curvature conditions. The research goes in the opposite direction as well. Some new Riemannian metrics might be induced by such Finsler structures.

Vendredi 10 novembre 14:00-15:00, Amphi 5 du CPT

Extracting scattering observables and resonance properties from lattice QCD

Max Hansen (CERN)

QCD, the quantum theory of the strong force, gives rise to a rich variety of short-lived resonance states. Understanding these in detail is of great interest, both for predicting backgrounds in new-physics searches and for gaining general insight into strong-force dynamics and phenomenology. The numerical technique of lattice QCD (LQCD), which has proven very successful in studying the properties stable hadrons, should also play an important role in reaching a comprehensive, quantitative picture for states that decay via the strong force. In this talk, I will review methods for calculating resonance properties in LQCD with a particular focus on three-particle decay channels. I will explain how the restriction to a finite volume can used as a tool, rather than an unwanted artifact. In addition, I will highlight the future steps required for achieving rigorous LQCD calculations of excited nucleon and exotic meson states.

Du 12 au 18 novembre, Cargèse

XIIIe Ecole de Cosmologie

XIIIe Ecole de Cosmologie

Ecole thématique du CNRS organisée par François Bouchet (IAP) et Roland Triay (CPT)

This school, which is open to international students, has as objectives the reciprocal upgrade and the development of a multidisciplinary community on the research lines promoted by the CNRS. It will favour the transfer of methods/techniques and the development of a multidisciplinary community that is either connected or interested in the massive data processing and statistical analysis. It will train new generations of researchers, notably on the basis of the existing Planck community. They will thus be able to take up the many challenges of all kinds that these ambitious projects involve, on theoretical aspects, instrumental ones and analysis of massive and complex data. The competencies (already obtained) in the processing of data are of interest to other scientific communities which have already expressed their interest, which will lead to the creation of networks for exchanges and collaborations.

Mercredi 15 novembre 13:00-15:00, Amphi 5 - CPT

Étude de problèmes inverses et directs pour différentes équations aux dérivées partielles

Yavar KIAN

Soutenance HDR Yavar Kian

Mercredi 15 novembre 15:30-17:00, Amphi 5 du CPT

Emergence : from spins to charges

Peter Holdsworth (ENS Lyon)

Emergence is one of the major buzz words of our times - but what does it mean ? Many things to many people is the answer. My working definition, which gives plenty of room for manoeuvre is : the appearance of unexpected many body phenomena, given the symmetries of the Hamiltonian and degrees of freedom at the microscopic level. In this colloquium I will discuss two topical examples in which the quasi-particle excitations of a model spin system with discrete symmetry appear as the topological charges of an emergent electro-magnetic field. In the planar clock model in two dimensions one finds the now famous Kosterlitz-Thouless phase transition which is a confinement - deconfinement transition of emergent electric charge. In the frustrated magnetic material, spin ice the quasi-particles appear to be freely moving magnetic charge - magnetic monopoles - and the system emerges as a magnetic Coulomb fluid in the grand canonical ensemble. With the addition of quantum fluctuations the emergent magneto-statics develops further into a complete analogue of quantum electrodynamics. I will aliment this discussion with experimental results from a wide range of systems.

Slides of the talk available at


Jeudi 16 novembre 14:00-16:00, Amphi 5 - CPT

Differential calculus on h-deformed spaces


Soutenance de thèse - Basile HERLEMONT

The ring Diff_h(n) of h-deformed differential operators of type A appears in the theory of reduction algebras. We construct the rings of generalized differential operators on the h-deformed vector space of gl-type. In contrast to the q-deformed vector space, where the ring of differential operators is unique, up to an isomorphism, the general ring of h-deformed differential operators Diff_h,σ(n) is labeled by a rational function σ in n variables, satisfying an over-determined system of finite-difference equations. We obtain the general solution of the system. We show that the center of Diff_h,σ(n) is a polynomial ring in n variables. We construct an isomorphism between certain localizations of Diff_h,σ(n) and the Weyl algebra Wn extended by n indeterminates. We present some conditions for the irreducibility of the finite dimensional Diff_h,σ(n)-modules. Finally, we show that finding analogue constructions for the ring Diff_h(n, N) of several copies of Diff_h(n) is a difficult task.

Vendredi 17 novembre 14:00-15:00, Amphi 5 du CPT

Holographic self-tuning of the cosmological constant

Francesco Nitti (APC, Paris)

I will present a brane-world setup, based on the gauge/gravity
duality, in which the four-dimensional cosmological constant is
neutralized by a dynamical self-adjustment mechanism. The model consists in a five-dimensional Einstein-Dilaton gravity coupled to a
four-dimensional brane on which ordinary matter and gauge fields are
localized. The brane position in the bulk is determined dynamically by the junction conditions, and flat-brane solutions exist for generic values of the brane vacuum energy. A regime with emergent 4-dimensional gravity is possible, due to the presence of an induced gravity term on the brane. The emergent 4d graviton acquires an effective mass, and a five-dimensional regime may exist at large and/or small scales. Analysis of scalar fluctuations allows to formulate conditions for perturbative stability of the flat solutions, which can be met in a broad range of the model parameters.

Mercredi 22 novembre 11:00-12:00, Amphi 5 du CPT

Asymptotics in the Problem on the Run-Up of Long Waves on a Shallow Beach

Vladimir Nazaikinskii (Ishlinsky Institute for Problems in Mechanics of the Russian Academy of Sciences)


We discuss near-boundary asymptotics for the solution of the Cauchy
problem for a degenerate wave equation with localized initial data
describing the run-up of long waves (e.g., tsunami waves) on a
shallow beach in the linear approximation. We show that problems of
this type are related to Dirac’s idea, realized by Fock more than
50 years ago, about the quantization of classical canonical

The talk is based on joint work with S.Yu. Dobrokhotov and A.A.
Tolchennikov. The research was supported by the Russian Science
Foundation (project 16-11-10282).

Mercredi 22 novembre 14:00-15:00, Amphi 5 du CPT

Singular "Punctured" Lagrangian Manifolds and the Asymptotics of Linear Waves near the Leading Edge Front

Serguei Dobrokhotov (Ishlinsky Institute for Problems in Mechanics of the Russian Academy of Sciences)


We consider the so-called Cauchy-Poisson problem in a basin with
uneven bottom for the propagation of surface water waves created by
a localized initial perturbation. We show that the asymptotic
solutions of such problems are associated with singular "punctured"
Lagrangian manifolds. The boundary of such a manifold can be viewed
as a new type of caustic (Lagrangian singularity) and determines
the leading front edge. We present efficient formulas for the waves
in a neighborhood of these objects, which permits easily analyzing
the dependence of the wave amplitude on the depth and dispersion.

The talk is based on joint work with V.E.Nazaikinskii,
S.Ya.Sekerzh-Zen’kovich and A.A. Tolchennikov.

Du 23 au 24 novembre, Campus St Charles

Problèmes inverses et domaines associés

5th workshop on the analysis of PDEs, with a strong emphasis on the study of inverse problems and control theory, to be held at the Fédération des Unités de Mathématiques de l’Agglomération Marseillaise (Frumam) in Marseilles, France, on November 23-24, 2017.

co-organized by E. Soccorsi (CPT)

Vendredi 24 novembre 11:00-12:00, Amphi 5 du CPT

On the regularization of BF theory

Philippe Mathieu (LAPTH, Université de Savoie)

The so-called Ponzano-Regge model is an attempt to define a quantum theory of gravity. Using the formalism of tetrades, the partition function of such a theory can be written in terms of a SU(2) BF action then can be reduced to a sum over the representations of SU(2) which is thus ill-defined. This is regularized replacing the representations of SU(2) by a period of periodic representations of Uq(SU(2)). This regularization is ad hoc since until then no one has been able to deal properly with path integral. The result is then written under the form of Turaev-Viro topological invariant.

We will see that, in the case of abelian BF theory, however, thanks to Deligne-Beilinson cohomology, we can clearly identify the degrees of freedom of the theory and extract the relevant toplogical information. The regularization appearing is then natural and is related to an abelian version of Turaev-Viro invariant in a way analogous to the so-called Deloup-Turaev reciprocity formula that connects abelian Chern-Simons theory on the one hand and an abelian version of Reshetikhin-Turaev invariant on the other hand.

Mercredi 29 novembre 14:00-15:00, Amphi 5 du CPT


Marcello Porta (Institut für Mathematik Universität Zürich)