# Prochains séminaires

 Condensed Matter seminar Thursday, September 29 at 11:00 at CPHT, Conference room Louis Michel Steven Thomson (Freie Universität Berlin) Recent Developments in Many-Body Localisation Many-body localisation (MBL) is a fascinating phenomenon where the presence of random disorder can prevent an isolated many-body quantum system from reaching thermal equilibrium. While there is a successful phenomenological model which explains many of the features observed in numerical calculations and experiments [1], the ultimate stability of many-body localisation in the thermodynamic limit has recently come into question [2]. In this talk, I will summarise some of my recent work aimed at understanding situations in which many-body localisation breaks down [3-5], and outline some of the big outstanding challenges which are yet to be addressed. [1] M. Serbyn et al., Phys. Rev. Lett. 111, 127201 (2013); D. Huse et al., Phys. Rev. B 90 174202 (2013) [2] J. Šuntajs et al., Phys Rev E 102, 062144 (2020) [3] S. J. Thomson, arXiv:2208.03234 [4] S. J. Thomson, arXiv:2208.11731 [5] C. Bertoni, J. Eisert, A. Kshetrimayum, A. Nietner & S. J. Thomson, arXiv:2208.14432
 AdS/CMT seminar on Monday September 26th at 11am at CPHT, Conference room Louis Michel Daniel Arean (Universidad Autonoma de Madrid) "Non-Hermitian Holography" Abstract:  The formulation and study of non-Hermitian PT-symmetric quantum theories has been the focus of both theoretical and experimental activity in recent years. In this talk I will present a minimal gravity dual of a non-Hermitian QFT, discuss its main features, and hopefully open up a discussion on future non-Hermitian directions.

 AdS/CMT seminar on Tuesday September 20th at 11am at CPHT, Conference room Louis Michel Benjamin Withers (University of Southamptoon) "Relativistic hydrodynamics: a singulant perspective" Abstract: As an effective theory of conserved currents near equilibrium, relativistic hydrodynamics is of wide applicability. I will give an overview of recent developments understanding the large-order behaviour of the hydrodynamic gradient expansion and present evidence that it is a divergent series in general. I will then introduce singulants as a way to gain analytic control over this large-order behaviour. Singulants obey simple equations of motion and govern the spacetime dependence of the large-order behaviour of on-shell constitutive relations.

 String theory seminar on Wednesday 18th 2022 at 14pm at CPHT, Conference room Jean Lascoux (Aile 0) Marc Geiller (ENS Lyon) "Relaxing the Bondi gauge in 3d and 4d gravity" Abstract: The Bondi gauge is a convenient choice of coordinates and line element to analyze the asymptotic structure of general relativity and aspects of gravitational radiation. Over the recent years several relaxations of the boundary conditions have been proposed, with the aim of understanding how general the asymptotic structure should be considered, and how large the asymptotic symmetry algebra can become. After presenting some motivations related to the understanding of charges, integrability, and flux in the covariant phase space formalism, I will review some recently proposed relaxations of the Bondi gauge in 3d and 4d gravity.

 String theory seminar on monday May 16th 2022 at 11am at CPHT, Conference room Louis Michel (Builging 6) Saso Grozdanov (University of Edinburgh) "Univalence bounds on transport and effective field theories" Abstract: Bounds on transport represent a way of understanding allowable regimes of quantum and classical dynamics. Numerous such bounds have been proposed, either for classes of theories or (by using general heuristic arguments) universally for all theories. Few are exact and inviolable. In this talk, I will present new methods for deriving exact, rigorous, and sharp bounds on all coefficients of hydrodynamic dispersion relations, including diffusivity and the speed of sound. These general techniques combine analytic properties of hydrodynamics and the theory of univalent (complex holomorphic and injective) functions. Concrete examples will include bounds that relate transport to quantum chaos through 'pole-skipping' as well as bounds without relation to chaos, such as the conformal bound on the speed of sound. I will also outline a set of general observations regarding the univalence properties of diffusion and sound in holographic models. Finally, I will discuss how these ideas could be generally applicable to constraining any effective field theory, not only hydrodynamics.

 AdS/CMT seminar on monday May 9th 2022 at 11am at CPHT, Conference room Louis Michel (Builging 6) Nick Poovuttiku (Durham University) "Anomaly “induce” transport in 2+1 dimensional QFT" Abstract: It is well-known that anomaly in 3+1 d(or other even dimensional spacetime) has profound effect on the transport properties in the hydrodynamic limit of a QFT (such as the chiral magnetic effect etc). I will discuss anomaly related phenomena that can also occur in odd spacetime dimensions (in particular 2+1 d). These includes anomaly induce transport involving higher-form symmetry, higher-group symmetry and ’t Hooft anomaly captured in characteristic class beyond Chern-Simons term.

 Cosmology seminar Monday January 3rd 2022 at 11am at CPHT, on Zoom (link) Matteo Fasiello (IFT Madrid) "Probing the Early Universe with Primordial Messengers" Abstract: Some of our best ideas on early universe physics are about to be put to the test by an unprecedented array of cosmological probes. The data these will collect span a vast range of scales, from the CMB to large scale structure, from pulsar timing arrays all the way to laser interferometers. This combined wealth of new information holds the potential to transform not just our understanding of cosmology, but also particle physics. Probing the earliest accessible epoch, the accelerated expansion known as inflation, is crucial: inflation can provide a cosmological portal to otherwise inaccessible energy scales. This is the “cosmological collider” idea. The spectacular success of the inflationary paradigm in explaining the origin of cosmic structure demands that we tackle a number of compelling questions still in need of an answer: what is the energy scale of inflation? What fields were active during inflation? In this talk I will review recent progress on the inflationary field content. I will survey different approaches to address the most pressing challenges and provide examples including axion-inflation models and, if time permits, the so-called effective theory approach. I will then focus on the key observables, starting with primordial gravitational waves, and discuss their prospects for detection.

 AdS/CMT seminar le mardi 14 décembre 2021 à 11h00 au CPHT, Salle de conférence Louis Michel Richard Davison (Heriot-Watt University, Scotland) "Chaos and pole-skipping in rotating black holes" Abstract: Out-of-time-ordered correlators of local operators (OTOCs) provide a way of characterising scrambling and chaos in quantum field theory states. For states with a classical, static black hole description, these correlators decay in a universal manner that is quantitatively related to a 'pole-skipping' property of the Green's function of the energy density operator. This is consistent with a hydrodynamic effective theory for chaos in these states. In this talk I will discuss how these results generalise to the rotating, thermal state dual to the Kerr-AdS black hole. In the limit of slow rotation I will present an explicit form of the OTOC and show how its form can be used to obtain exact constraints on the dispersion relations of the collective modes that carry energy.

 AdS/CMT seminar le vendredi 10 décembre 2021 à 11h00 au CPHT, Salle de conférence Louis Michel Sebastian Grieninger (IFT Madrid) "(Pseudo)-Spontaneous U(1) Symmetry Breaking in Hydrodynamics and Holography" Abstract: We investigate the low-energy dynamics of systems with (pseudo)-spontaneously broken U(1) symmetry. First, we consider the purely spontaneous case which corresponds to a superfluid where we compute the support of the hydrodynamic modes on the different field theory operators across the phase diagram. In the pseudo-spontaneous case, we construct a hydrodynamic framework and consider two generalizations of the standard holographic superfluid model to incorporate explicit breaking. In all cases, we find agreement between hydrodynamics and holography. Furthermore, we verify that phase relaxation arises only due to the breaking of the inherent Goldstone shift symmetry. The interplay of a weak explicit breaking of the U(1) and phase relaxation renders the DC electric conductivity finite but does not result in a Drude-like peak. In this scenario we show the validity of a universal relation between the phase relaxation rate, the mass of the pseudo-Goldstone and the Goldstone diffusivity.

 Virtual String seminar le jeudi 9 décembre 2021 à 16h00 au CPHT, Salle de conférence Louis Michel Shu-Heng Shao Anomalies and Emergent Symmetries on the Lattice and in the Continuum Abstract: We consider various standard and exotic lattice models, and deform them using an approach generalizing the Villain formulation. The new lattice models exhibit many properties that were thought to be exclusive to the continuum field theories. These include exact winding/magnetic symmetries, anomalies, and new dualities. We apply this approach to the standard XY model, ZN clock model, gauge theories, and exotic models related to fractons. https://us06web.zoom.us/j/82331562209?pwd=UENqcGZpRVZ0VXlkQzZESGNLTXBVUT09

 Séminaire des cordes le lundi 22 novembre 2021 à 11h00 au CPHT, Salle de conférence Louis Michel Chern-Simons supergravity and black holes with unbroken supersymmetriesOlivera Mišković (PUCV, Valparaiso, Chile) We study particular supersymmetric extension of Einstein-Gauss-Bonnet AdS gravity in five dimensions. The theory admits black hole solutions with non-trivial topological properties, which are also BPS states that leave some of the supersymmetries unbroken. We analyse physical properties of these solutions, such as their conserved charges and topological numbers. We find many similarities of these solutions with standard supergravity black holes, and also with three-dimensional BTZ geometries.   Conformal renormalization in AdS gravityRodrigo Olea (UNAB, Santiago, Chile) We present evidence that the renormalization of Einstein-AdS gravity can be derived from conformal structures in the bulk. In point of fact, by applying a holographic mechanism which reduces Conformal Gravity to its Einstein sector in 4 and 6 dimensions, the Einstein-AdS action is naturally endowed with the correct counterterms.

 Anh-Dung Le soutiendra publiquement ses travaux de thèse le vendredi 19 novembre 2021 à 14h30 au CPHT, Salle de conférence Louis Michel. Titre de la thèse : "Statistical properties of partonic configurations and diffractive dissociation in high-energy electron-nucleus scattering" Directeur de thèse : Stéphane Munier Composition du Jury (1) Stéphane Munier, CNRS (France), Directeur de thèse (2) Yuri Kovchegov, The Ohio State University (USA), Rapporteur (3) Tuomas Lappi, Jyvaskyla University (Finland), Rapporteur (4) Nestor Armesto, Universidade de Santiago de Compostela (Spain), Examinateur (5) Cédric Lorcé, Ecole polytechnique (France), Examinateur (6) Grégory Schehr, CNRS (France), Examinateur Abstract "In the high-energy scattering of a quark-antiquark color dipole off a hadron, the quantum states of the former are represented by a stochastic set of dipoles generated by a binary branching process, in the so-called color dipole model of quantum chromodynamics (QCD). It was found that there is a profound connection between this QCD description and the branching-diffusion processes studied in statistical physics from which different properties of the scattering in the high-energy regime are revealed. Our work in this thesis is aimed to exploit the cross-fertilization between QCD and statistical physics to study the detailed partonic content of the Fock states of a color dipole subject to high-energy evolution in the scattering off a large nucleus. We also produce predictions for diffractive dissociation in electron-ion collisions, based on the QCD dipole picture. In the first place, the scattering events of a color dipole, when parameters are set in such a way that the total cross section is small, are triggered by configurations containing large-transversesize dipoles. The latter are due to rare partonic fluctuations, which look different as seen from different reference frames, from the rest frame of the nucleus to frames in which the rapidity is shared between the projectile dipole and the target nucleus. It turns out that the freedom to select a frame allows to deduce an asymptotic analytic expression for the rapidity distribution of the first branching of the slowest parent dipole of the set of those which scatter, which provides an estimator for the correlations of the latter. In another aspect, the study implies the importance of the characterization of particle distribution near the extremal particles, referred to as the \tip", in the states generated by the QCD dipole branching, and more generally, by any one-dimensional branching random walk model. To this aim, we develop a Monte Carlo algorithm to generate the tip of a binary branching random walk on a real line evolving to a predefined time, which allows to study both rare and typical configurations. The above statistical description proves advantageous for calculating diffractive cross section demanding a minimal rapidity gap Y0 and the distribution of rapidity gaps Y_{gap} in the diffractive dissociation of a small dipole off a large nucleus, in a well-defined parametric region. They are the asymptotic solutions to the Kovchegov-Levin equation, which was established more than 20 years ago to describe the diffractive dipole dissociation at high energy. Additionally, we present predictions for the distribution of rapidity gaps in realistic kinematics of future electron-ion machines, based on the numerical solutions to the original Kovchegov-Levin equation and of its next-to-leading extension taking into account the running of the strong coupling. The outcomes for the former reflect in a qualitative way our asymptotic analytical result already at rapidities accessible at future electron-ion colliders."

 Séminaire de Physique des Particules CPHT-Ecole Polytechnique le jeudi 18 novembre 2021 à 11h00 exceptionnellement au CMLS Salle de conférence Laurent Schwartz Tuomas LAPPI "Loops in light cone perturbation theory" Abstract: Light cone perturbation theory is the method of choice for perturbative calculations in the high energy limit of QCD, where a simple probe, e.g. a quark or virtual photon, interacts with a nonperturbative color field. This talk concentrates on recent progress in calculating the total deep inelastic scattering cross section in the color dipole picture at next to leading order in perturbation theory. For massless quarks this cross section has been computed and used to describe HERA data. For massive quarks the calculation is close to being complete, with results for a longitudinally polarized photon already published. The calculation for massive quarks poses both technical and conceptual challenges related to mass renormalization in light cone perturbation theory.

 Séminaires des jeunes chercheurs du CPHT Le 1er séminaire des jeunes chercheurs du CPHT aura lieu le 27 octobre 2021 à 15h00 à la Salle de conférence Louis Michel avec trois présentations par les doctorants : Majdouline Borji : Perturbative renormalization of the semi-infinite massive scalar field theory using the flow equations Pauline Besserve : Unraveling correlated materials’ properties with noisy quantum computers William Focillon : Potential Linear and Angular Momentum in the Scalar Diquark Model Le séminaire sera suivi d'une goûter.

 Séminaire des cordes le vendredi 8 octobre 2021 à 15h00 au CPHT, Salle de conférence Louis Michel Anastasios Petkou "On scale, conformal and Weyl invariance in QFT" Abstract: Scale, conformal and Weyl invariance play a central role in Quantum Field Theories, and they are omnipresent in AdS/CFT correspondence. Through various examples I will review various issues and possible misconceptions regarding the interrelationships between these three important notions and connect them to some recent investigations.

 Soutenance de thèse au CPHT  Thibaut coudarchet soutiendra publiquement ses travaux de thèse le 30 septembre 2021 à 14h00 à l'Ecole polytechnique, Amphi Lagarrigue. Titre de la thèse : Théorie des cordes : brisure de supersymétrie, stabilisation des modules et aspects cosmologiques Directeur de thèse : Hervé Partouche Mots-clés : Théorie des cordes,Brisure de supersymétrie,Modules,Cosmologie Participer à la réunion Zoom pour la soutenance de thèse : 30 sept. 2021 02:00 PM Paris Zoom link:https://us02web.zoom.us/j/81787410532 ID: 817 8741 0532 Composition du Jury M. Hervé PARTOUCHE, École polytechnique,Directeur de thèse Mme Mariana GRAÑA,IPhT, CEA/Saclay, Rapporteure M. Dan ISRAËL,LPTHE, Sorbonne Université, Rapporteur M. Ignatios ANTONIADIS, LPTHE, Sorbonne Université, Examinateur M. Augusto SAGNOTTI, École Normale Supérieure de Pise, Examinateur M. Jan TROOST,LPENS, École Normale Supérieure, Examinateur M. Toumbas NICOLAOS, Département de physique, Université de Chypre, Examinateur

 Soutenance de thèse au CPHT  Philipp Klein soutiendra publiquement ses travaux de thèse le 8 septembre 2021 à 14h00 au CPHT, Salle de conférence Louis Michel. Title: Topological proximity effect in bilayer systems and stochastic approach to interacting topological phasesKeywords: Topological phases, bilayer model, Mott physics, strongly-correlated phases PhD Supervisor: Karyn Le Hur, CPHT Directrice de Recherche et Professeure PCC Ecole Polytechnique Participer à la réunion Zoom pour la soutenance de these : https://us02web.zoom.us/j/88483206477 ID de réunion : 884 8320 6477 Jury Members (participation via Zoom):   - Sylvain Capponi, Professeur, Toulouse, President du Jury - Nathan Goldman, Professeur, Universite Libre de Bruxelles (reviewer) - Mark-Oliver Goerbig, Directeur de recherches CNRS et professeur PCC Ecole Polytechnique, LPS Orsay (reviewer) - Thierry Jolicoeur, Directeur de Recherches CNRS, CEA Saclay - Luca Perfetti, Professeur, LSI Ecole Polytechnique - Timan Ziman, Directeur de Recherches CNRS, Institut Laue Langevin - Silke Biermann, Professeure Ecole Polytechnique, Invited

 Soutenance de thèse au CPHT  Louis Villa soutiendra publiquement ses travaux de thèse intitulés "Out-of-equilibrium dynamics and quench spectroscopy of ultracold many-body quantum systems" le 9 juillet 2021 à 14h00 au CPHT, Salle de conférence Louis Michel. Thèse de doctorat de l’Institut Polytechnique de Paris préparée à l’Ecole Polytechnique, au Centre de Physique Théorique (groupe Matière condensée). Composition du Jury : - David Clément, Maître de Conférences, Institut d’Optique Graduate School (Laboratoire Charles Fabry), Rapporteur - Nicolas Pavloff, Professeur, Université Paris-Saclay (Laboratoire de Physique Théorique et Modèles Statistiques), Rapporteur - Gabriele De Chiara, Reader, Queen’s University of Belfast (Centre for Theoretical Atomic, Molecular and Optical Physics), Examinateur - Luca Tagliacozzo, Ramon y Cajal Fellow, Universitat de Barcelona (Departamento de Fisica Cuantica i Astrofisica), Examinateur - Patrizia Vignolo, Professeure, Université de Nice-Sophia Antipolis (Institut Non-Linéaire de Nice), Examinatrice - Laurent Sanchez-Palencia, Directeur de recherche, Ecole Polytechnique (Centre de Physique Théorique), Directeur de thèse Résumé de la thèse / Abstract

 Journée scientifique de l’Institut Polytechnique de Paris : A la croisée des sciences Une première édition digitale aura lieu le  MARDI 16 JUIN DE 14H A 16H30 Découvrez le programme et inscrivez-vous ici Organisée par des chercheurs pour les chercheurs et les doctorants, l’objectif de cette journée conviviale est de réunir les dix communautés de l’Institut afin d’offrir un panorama de le recherche réalisée au sein de ses laboratoires. Au programme : des présentations dynamiques de 5 minutes sur des thématiques variées montrant la richesse des recherches de nos laboratoires, des discours scientifiques croisés faisant le lien entre des sujets de plusieurs disciplines, des échanges autours de posters scientifiques, etc. Plus de détails seront bientôt communiqués. Comité d’organisation : Isabelle Bloch (Telecom Paris), Jean-René Chazottes (École polytechnique), Arnak Dalalyan (Ensae), Maryline Laurent (Telecom SudParis), Jean-François Semblat (Ensta Paris), avec l’aide de Chloé Aubisse et Solange Ricard (direction de la communication de l'École polytechnique). Une édition en présentiel aura lieu à une date qui reste à définir en fonction de l'évolution des conditions sanitaires.

 Soutenance de thèse au CPHT en visioconférence Charles Marteau (groupe Théorie des cordes) Boundary structures and holographic fluids in gravity Abstract This thesis is devoted to the study of several aspects of dynamical spacetimes with boundaries. An emphasis is put on asymptotic boundaries such as the conformal boundary of AdS or the null infinity in flat space. In AdS the geometry of the conformal boundary is pseudo-Riemannian since the boundary is time-like. In flat space, we will show how the geometry of the null infinity can be described in terms of Carroll structure. The latter emerges as the ultra-relativistic limit, or c → 0 limit, of a pseudo-Riemannian geometry. In particular, the flat limit in the bulk maps to this ultra-relativistic limit on the boundary. We will also see how the symmetries of asymptotically flat gravity translate into global symme- tries of this exotic boundary geometry. This analysis is of central importance in fluid/gravity correspondence since the fluid is expected to live on the boundary. In this context we find integrability conditions on the boundary fluid that allow for a resummation of the so-called Derivative Expansion in AdS. The flat limit gives rise to the notion of Carrollian fluid on the boundary whose hydrodynamical expansion maps to a flat version of the Derivative expansion in the bulk, thus providing a no- tion of fluid/gravity correspondence in flat space. A second type of boundary that we study is the one formed by the horizon of a black hole. There, another type of fluid/gravity correspondence exists: the membrane paradigm. We revisit this con- cept and propose a novel interpretation of the Damour–Navier–Stokes equation in terms of ultra-relativistic conservation laws. Jury Dionysios ANNINOS, Kings College, Londres Glenn BARNICH, Université Libre de Bruxelles Daniel GRUMILLER, TU Wien, Vienne Niels OBERS, Niels Bohr Institute, Copenhague et Nordita, Stockholm Marios PETROPOULOS, École Polytechnique, IP Paris (directeur de thèse) Andrea PUHM, École Polytechnique, IP Paris Organisation La soutenance aura lieu par conférence zoom le vendredi 19 juin 2020 à 10h30. L’accueil sera assuré dès 10h. Les retardataires ne seront pas admis en salle avant l’entracte. Les coordonnées de la connexion peuvent être obtenues sur demande auprès de Malika Lang, Charles Marteau ou Marios Petropoulos.

 Lectures on Duality for interacting particle systems: the algebraic approach, via examples, by Frank Redig (CPHT, Chaire d’Alembert, 1 January-31 June 2020) Frank Redig will give six lectures, grouped into three sessions, at the following dates : 19 May, 26 May, 2 June, from 10:30 to 12:30, in the conference room Louis Michel. The lectures will be centred around the theory and applications of duality in the context of interacting particle systems and non-equilibrium statistical physics models. Duality is a powerful tool in Markov process theory, allowing to connect two processes (the process under study and its dual) via a so-called duality function. Often the dual process is simpler, e.g., in systems coupled with reservoirs in the dual the reservoirs are replaced by absorbing boundaries, or in infinite interacting systems, the dual is a system of finitely many particles, or in the context of diffusion processes, the dual is a simple discrete jump process. We show how to understand dualities from the point of view of an underlying Lie algebra of symmetries (operators commuting with the generator). This approach gives several new dualities, and new duality functions, such as orthogonal duality functions. It also allows to constructively define processes with dualities, and to find correct’’ asymmetric versions of symmetric models with dualities (via so-called q-deformation). We will explain this theory starting from simple examples (such as independent random walkers, exclusion process, inclusion process), and provide several applications in the description of non-equilibrium steady states as well as in hydrodynamic limits and fluctuation fields. Lecture 1: Introduction, motivation, some background from Markov process theory Lecture 2: Duality: definition, duality and symmetries, duality and intertwining, duality and change of representation. Examples. Lecture 3: Dualities for independent random walkers: self-duality, duality with deterministic system, averaging models. Applications to hydrodynamic limits and fluctuation fields and to ergodic theory. Lectures 4-5: The symmetric inclusion process (SIP) and its dual processes: Lie algebraic construction via co-product of the Casimir. Discrete and continuous representations, diffusion processes dual to SIP. Thermalization, models of KMP type, inhomogeneous systems. Lecture 6: Non-equilibrium steady states: duality with reservoirs. Consistency, orthogonal polynomial duality. Universal properties of correlation functions of non-equilibrium steady states.

 Séminaire  de Physique Statistique CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel Lundi 16 mars 14h Annnulé Speaker: Grégory Schehr, LPTMS Title: Large deviations of the top eigenvalue of random matrices and applications in statistical physics Abstract: The statistical properties of the largest eigenvalue of a random matrix are of interest in diverse fields such as in the stability of large ecosystems, in disordered systems and related stochastic growth processes, in statistical data analysis and even in string theory. In this talk I will discuss the developments in the theory of extremely rare fluctuations (large deviations) of the largest eigenvalue using a Coulomb gas approach. I will discuss in particular the third-order phase transition which separates the left tail from the right tail, a transition akin to the so-called Gross-Witten-Wadia phase transition found in 2-d lattice quantum chromodynamics.

 Séminaire  de Physique Mathématique CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel Mercredi 11 mars 14:00-15:00 : Bart van Ginkel Title: Hydrodynamic limit of the Symmetric Exclusion Process on compact Riemannian manifolds. Abstract: In this talk I will first explain the concept of the hydrodynamic limit of an interacting particle system. The idea is that one wants to show that when both space and time are rescaled (appropriately), the limiting densities of particles satisfy some PDE. This will be illustrated with the Symmetric Exclusion Process. Then we move this basic particle system to a hard context: Riemannian manifolds. I will highlight which challenges arise in the curved setting and how we deal with them. Joint work with Frank Redig. 15:00-16:00 : Rik Versendaal Title: Large deviations for geodesic random walks. Abstract: The theory of large deviations is concerned with the limiting behaviour on the exponential scale of a sequence of random variables. A fundamental result is Cramér’s theorem, which states that the empirical mean of a sequence of i.i.d. random variables satisfies a so called large deviations principle. Mogulskii’s theorem is concerned with the corresponding path space large deviations. To study the analogue of these theorems for a Riemannian manifold, we introduce a generalization of random walks to a manifold, called geodesic random walks. We present the analogues of Cramér’s and Mogulskii’s theorem for geodesic random walks and write down the rate function for these large deviations principles.

 Séminaire  de Physique Mathématique CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel Mercredi 4 mars 2020, 11h Ariane Carrance (Laboratoire de Mathématiques d'Orsay, Université Paris Sud) Title: La carte brownienne, un modèle de gravité quantique 2D de plus en plus universel Abstract: La question fondamentale de l'unification de la mécanique quantique et de la relativité générale en une théorie cohérente de la gravité quantique peut se traduire en divers problèmes concrets plus ou moins ambitieux. Ainsi, une approche possible est de chercher à définir un espace métrique aléatoire (et non quantique), continu, qui puisse être interprété comme un espace-temps aléatoire. Une manière plus spécifique d'obtenir un tel espace-temps est de le construire comme limite d'échelle d'espaces métriques discrets. En dimension 2, c'est ainsi que la carte brownienne s'obtient comme limite d'échelle de nombreuses familles de cartes planaires. Après avoir introduit les notions nécessaires pour comprendre ces limites, je présenterai un résultat qui étend la classe d'universalité des modèles discrets qui convergent vers la carte brownienne, et la relie plus explicitement à des modèles reposant sur le calcul de Regge, tels que les Triangulations Dynamiques, ainsi qu'au cas 2D des modèles de tenseurs colorés.

 Séminaire de Théorie des cordes CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel Mardi 3 mars 2020, 11h Giuseppe Policastro (ENS) Title: Quantum complexity and holography Abstract: I will discuss the motivations for introducing the notion of quantum complexity in physics, coming from the issues related to the information loss paradox in black holes. I will introduce the definition of complexity, the different proposals for its holographic computation, its inherent ambiguity, then present the computation for the case of a boundary/defect CFT.

 Séminaire de Physique Mathématique JEUDI 13 FEVRIER 14h00 SALLE LOUIS MICHEL BALT VAN REES QANTUM FIELD THEORY in ANTI-DE SITTER and the S-MATRIX Abstract: We discuss results obtained by considering gapped QFTs in a fixed Anti-de Sitter background. Much like in the AdS/CFT correspondence, we can naturally define 'boundary' observables that exhibit conformal invariance in one dimension less. These observables can be analyzed using conformal bootstrap techniques which results in new non-perturbative bounds on the strength of the coupling constants in a general QFT. When we send the AdS curvature to zero the boundary observables should morph into the S-matrix of the flat-space QFT. We will discuss the different ways in which this connection can be made explicit, and how it might end up teaching us new lessons about the non-perturbative structure of scattering amplitudes. JEUDI 13 FEVRIER 15h15 SALLE LOUIS MICHEL JÜRG FRÖHLICH THE FOURTH PILLAR which QUANTUM MECHANICS RESTS UPON Abstract: Traditionally, the three concepts of states, observables and unitary evolution form the pillars Quantum Mechanics is built upon. It is well known that they do not suffice to solve, for example, the so-called measurement problem. In this talk I will describe a fourth fundamental concept, proposed only recently, namely the "Principle of Diminishing Potentialities". I will then show how it enables one to come up with a precise notion of "events" in Quantum Mechanics and with a new understanding of the time evolution of states of isolated systems. As results, the "measurement problem" and the unitarity- or information paradox disappear, and a "Quantum Mechanics without Observers" emerges.

 Colloquium du CPHT CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel 6 février 2020 14h Zaki Leghtas "Quantum computing with Schrödinger cat states" Superconducting qubits are one of the most promising platforms to implement quantum technologies. Quantum processors of tens of qubits are now available, and exciting applications with these intermediate size systems are in perspective. However, many algorithms, including all those with a proved quantum speed-up, require extremely low error rates. This will most likely require quantum error correction (QEC). Unfortunately, current QEC architectures require daunting overheads in physical qubits and control electronics. The goal of this research is to reduce this overhead, and our approach is based on two key ideas. First, we redundantly encode quantum information in Schrödinger cat states embedded in superconducting resonators. Second, we engineer non-linear dissipation to protect and manipulate this information.

 IQUPS new series of courses IQUPS organises a new series of courses: on November26 and December 10, 12 and 17 (2019), two courses will take place in the same mornings from 9:15 to 12:30: Quantum fluids of light by Jacqueline Bloch (C2N, Palaiseau) and Quentin Glorieux (LKB, Paris) Open Quantum Systems: Foundations and Applications by Laurent Sanchez-Palencia (Centre de Physique Théorique, Institut Polytechnique de Paris, Palaiseau) The courses, in English, will take place at the grand amphi in C2N (new site near IOGS and Polytechnique). For PhD students: the courses are labelled "complément de formation initiale" by the doctoral schools EDPIF et EDOM. To attend the courses, please register on-line or send a mail to iqups@universite-paris-saclay.fr. Abstracts: Open Quantum Systems: Foundations and Applications (by Laurent Sanchez-Palencia) The dramatic progress in the design of materials and synthetic simulators now allows to realize controlled quantum systems rather well isolated from their environment. Yet, the coupling to the environment (bath) cannot be ignored and open systems are ubiquitous in Nature. It gives rise to a rich competition between coherence and dissipation, and novel dynamical effects. While coupling a system to a bath typically yields decoherence, recent works have shown that dissipation can be engineered to control many-body systems and engineer quantum entanglement. The aim of this course is to give an introduction to open quantum systems. We shall introduce the formalism and discuss applications to quantum technologies. Lecture 1: Open systems and stochastic processes Lecture 2: Master equation formalism: Krauss operators and Lindblad form Lecture 3: Stochastic Schrödinger equation and quantum trajectories Lecture 4: Engineered dissipation as a resource for entanglement Quantum fluids of light (by Jacqueline Bloch and Quentin Glorieux) When confining photons in semiconductor lattices, it is possible to strongly modify their physical properties. Photons can behave as finite or even infinite mass particles, photons can propagate along edge states without back scattering, photons can become superfluid and behave as massive interacting particles. These are just a few examples of properties that we can imprint into fluids of light in semiconductor lattices. Such manipulation of light present not only potential for applications in photonics, but great promise for fundamental studies. One can invent artificial media with very exotic physical properties at the single particle level and progress toward the generation of multi photons correlated states. One can also simulate complicated Hamiltonians with light to explore problems not accessible with ultra cold atoms. The three first lectures will be delivered by Jacqueline Bloch and dedicated to the physics of quantum fluids of light(also called polaritons) in semiconductor microcavities . Quentin Glorieux, LKB, Paris will give the last lecture and describe a different platform for the study of quantum fluids based on photons propagating through a hot vapor of Rubidium atoms in the paraxial approximation Lecture 1 (J. Bloch): Introduction to cavity polaritons, linear properties and lattice engineering Lecture 2 (J. BLoch): Polariton superfluidity and Bose Einstein condensation Lecture 3 (J. Bloch): Emulation of different Hamiltonians using polariton lattices; perspectives for quantum correlations Lecture 4 (Q. Glorieux) : Quantum fluids of light in hot atomic vapor : propagating geometries

 Colloquium du CPHT CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel mardi 19 novembre à 11h Mette Gaarde, Professeure à l'Université d'État de la Louisiane "Making movies of ultrafast dynamics: tracking and controlling femtosecond absorption and emission processes" Immense progress in the development of femtosecond and attosecond light sources means that scientists are now routinely directing movies of ultrafast electron and molecular dynamics as it is unfolding on its natural time scale. For example, intense femtosecond X-ray pulses from free-electron lasers can directly take pictures of molecular structural changes, and attosecond extreme ultraviolet (XUV) pulses have been used to time the photoelectric effect. I will start this talk with a brief overview of different types of dynamics that are of interest to the ultrafast community and how to probe them. Then I will discuss an example of opto-optical modulation: how to manipulate the femtosecond time-dependence of absorption and emission processes in gases, with an optical laser pulse, in order to control the temporal and spatial properties of an XUV pulse.

 Séminaire des cordes CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel mardi 8 octobre 2019 à 11h00 Elias Kiritsis (APC) "Emergent gravity and hidden sector" I will discuss ideas on how gravity can be an emergent interaction in QFT, what guarantees the emergent diffeomorphism invariance, what are its general features and properties and what could be the possible implications for realistic gravitational physics.

 Gravity and Strings Conference 26 septembre 2019, Ecole Polytechnique, CPHT, Salle Louis Michel 10AM - 6PM Organized by Luca Ciambelli   Speakers :   Carlo Angelantonj Stéphane Detournay Rodrigo Olea Anastasios Petkou Marios Petropoulos Céline Zwikel   Contact : luca.ciambelli@gmail.com

 Séminaire des cordes CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel mardi 5 février 2019 à 11h00 Gary Horowitz (de UCSB) "Singularities and Cosmic Censorship"

 Séminaire de Physique des ParticulesCPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Jeudi 10 janvier 2019 à 11hCPHT, Ecole Polytechnique, Salle de Conférence Louis Michel (Bât. 6) Paul Hoyet (University oh Helsinki) Bound states and perturbation theory abstract

 COURS THEMATIQUES Les 4 et 11 décembre 2018, une série de leçons sera organisée sur le thème Many-body quantum chaos: from black holes to hydrodynamics Sašo Grozdanov – MIT   Abstract: Chaos is a well-understood phenomenon within classical physics. According to its simplest definition, it stems from the dynamics of particles, which follow trajectories with extreme sensitivity to initial conditions. Two commonly associated phenomena are the exponential Lyapunov divergence of initially nearby trajectories and the butterfly effect. In many-body quantum physics, the situation is completely different. There, the very definition of what quantum chaos is remains unclear. Even more elusive are its characterisation and classification. In this four-hour lecture course, I will discuss exciting recent revival of interest in addressing these questions, which was largely ignited by studies of the physics of black holes. First and second lectures: Tuesday December 4 11:00 & 14:00 – salle Louis Michel – CPHT A short review on classical chaos: Lyapunov exponents and the butterfly effect. A measure of quantum chaos: the out-of-time-ordered correlation function (OTOC). When is the OTOC a good measure of chaos? An example of a quantum (maximally) chaotic system: the Sachdev-Ye-Kitaev model. A primer on black-hole physics and gauge-string duality (holography). Calculation of OTOCs in holography and the Maldacena-Shenker-Stanford bound.   Third and fourth lectures: Tuesday December 11 11:00 & 14:00 – salle Louis Michel – CPHT Hydrodynamics and collective dynamics of energy and momentum. Holographic aspects of hydrodynamics. A new universal property of Einstein gravity and connection between (complex) analytic properties of hydrodynamics and quantum chaos: “pole-skipping”.

 Séminaire de Physique des ParticulesCPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Vendredi 23 novembre 2018 à 11hCPHT, Ecole Polytechnique, Salle de Conférence Louis Michel (Bât. 6) Savvas Zafeiropoulos (Université de Heidelberg) Parton pseudo-distribution functions from Lattice QCD The light-cone denition of Parton Distribution Functions (PDFs) does not allow for a direct ab initio determination employing methods of Lattice QCD simulations that naturally take place in Euclidean spacetime. In this presentation we focus on pseudo-PDFs where the starting point is the equal time hadronic matrix element with the quark and anti-quark elds separated by a nite distance. We focus on Ioe-time distributions, which are functions of the Ioe-time , and can be understood as the Fourier transforms of parton distribution functions with respect to the momentum fraction variable x. We present lattice results for the case of the nucleon and we also perform a comparison with the pertinent phenomenological determinations.

 Journée des thèses 2018 La Journée des Thèses aura lieu au CPHT le jeudi 15 novembre 2018 à partir de 10h00 dans la salle de conférence Louis Michel. Format : 10 minutes/exposé + 5 minutes pour les questions              10h-12h30 : · [10h00-10h30] : Rencontre entre les doctorant.e.s et la DDPD (Direction Déléguée Programme Doctoral) · [10h30-10h45] Luca CIAMBELLI : AdS/CFT : The fluid road to holography · [10h45-11h] Ariane SORET : Superconductivity and out-of-equilibrium systems · [11h-11h15] Jan MAELGER : QCD from perturbation theory · [11h15-11h30] Pablo GUERRERO RODRIGUEZ : The non-linear regime of quantum chromodynamics in the context of relativistic heavy-ion collisions · [11h30-11h45] Guillaume BROCHARD : Kinetic effects of energetic particles on magneto-hydrodynamics instabilities in tokamak plasmas · [11h45-12h] Jakob STEINBAUER : Slave-rotor techniques in many-body electrons systems · [12h-12h15] Quentin BONNEFOY : Topics in BSM physics · [12h15-12h30] Julien DESPRES : Far-from-equilibrium dynamics in quantum lattice models 12h30-14h : pause 14h-15h30 : · [14h-14h15] Hepeng Low dimensional ultracold atom gases ·         [14h15-14h30] Grégoire VARILLON : Non-modal hydrodynamic stability analysis for ablation flows relative to inertial confinement fusion · [14h30-14h45] Fan YANG : Topological phases and interaction effects · [14h45-15h] Marcello TURTULICI : "Ab-initio" materials simulations for correlated electron systems with vacancies · [15h-15h15] Mufei LUO : Auto-resonance in three-wave interactions with bandwidth · [15h15-15h30] Charles MARTEAU : Flat holography 15h30-15h45 : pause · [15h45-16h] Thibaut COUDARCHET : Cosmological Higgs mechanism and dark matter creation in a string theory framework · [16h-16h15] Philipp KLEIN : Topological effects in layer systems · [16h30-16h45] Louis VILLA : Strongly interacting quantum systems in 1d 16h45 : goûter

 COURS THEMATIQUES Au cours de l’automne 2018, une série de leçons sera organisée sur le thème Stochastic quantisation of QFTs & applications to quantum gravity and early cosmology Laurent Baulieu – LPTHE UPMC Fourth and fifth lectures Stochastic quantisation and gauge fields  Vendredi  9 novembre 11:00 & 14:00 – salle Louis Michel – CPHT Plan: • The role of instantons in stochastic quantisation. • Fermions in stochastic quantisation and the kernels for their Fokker–Planck evolution. • Gauge theories in stochastic quantisation and their equivariant cohomology. • Supersymmetric theories in stochastic quantisation and the fate of their auxiliary fields. • What do we learn from the stochastic quantisation of gauge fields? Plus d'informations

 Séminaire des cordes CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel Doron Gepner (Weizmann Institute) Three blocks solvable lattice models and Birman—Murakami—Wenzl algebra   Birman--Murakami--Wenzl (BMW) algebra was introduced in connection with knot theory. We treat here interaction round the face solvable (IRF) lattice models. We assume that the face transfer matrix obeys a cubic polynomial equation, which is called the three block case. We prove that the three block theories all obey the BMW algebra. This result is important to the solution of IRF lattice models and the development of new models, as well as to knot theory.

 COURS THEMATIQUES Au cours de l’automne 2018, une série de leçons sera organisée sur le thème Stochastic quantisation of QFTs & applications to quantum gravity and early cosmology Laurent Baulieu – LPTHE UPMC Second and third lectures Basics on stochastic quantisation  Vendredi 12 octobre - 11:00 & 14:00 – salle Louis Michel – CPHT Plan: • Langevin equation for quantum field theory Euclidean correlators (Parisi–Wu approach) & link with Fokker–Planck formulation. • Convergence properties of correlation functions at infinite stochastic time & emergence of Minkowski time. • More recent formulation of stochastic quantisation with a path integral representation using the stochastic time as a bulk time. • Examples. Plus d'informations

 COURS THEMATIQUES Au cours de l’automne 2018, une série de leçons sera organisée sur le thème Stochastic quantisation of QFTs & applications to quantum gravity and early cosmology Laurent Baulieu – LPTHE UPMC First lecture Thursday October 4 Motivations in early cosmology and quantum gravity Jeudi 4 octobre 2018 à 11h00 CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel Abstract: Euclidean quantum gravity might be defined by a stochastic quantisation that is governed by a higher-order Langevin equation rather than by a first-order stochastic equation, giving a transitory phase where Minkowski time cannot be defined, so the parameter that orders the evolution of quantum gravity phenomena is the stochastic time. This may enlarge the definition of causality in the period of primordial cosmology. For stochastically quantised gravity, one predicts a transition from an oscillating quantum phase to a classical one, where the Minkowski time has emerged. In the beginning, the universe is diluted, filled with scattered classical primordial black holes. The smallest ones decay then quickly in matter with a standard quantum-field-theory evolution, whereas the heaviest ones are stable and remain therefore in the Universe till our era. In order to give substance to this idea we examine the meaning of a second-order Langevin equation in zero dimensions for defining precisely what is second-order stochastic quantisation in a solvable case. Plus d'informations

 Séminaire des cordes Jeudi 20 septembre 2018 à 11h00 CPHT, Ecole Polytechnique, Salle de Conférence Jean Lascoux, Aile Zéro Rodrigo Olea (U. Andres Bello, Chile) Holographic Entanglement Entropy and Topological Terms   We consider the renormalization of holographic entanglement entropy (HEE) for Conformal Field Theories in odd dimensions, dual to Einstein gravity with negative cosmological constant in one dimension higher. We make explicit the equivalence between renormalized entropy and the renormalized area of the entangling surface. In particular, for constant-curvature surfaces, HEE is fully determined in terms of a single topological number (Euler characteristic).

 Séminaire des cordes Mardi 11 septembre 2018 à 14h30 CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel Gaston Giribet (INFN. Roma) T Tbar deformations, AdS/CFT and correlation functions   I will consider irrelevant deformations of AdS3/CFT2 correspondence that interpolate between a CFT2 in the IR and a theory with Hagedorn spectrum in the UV. For such theories, I will explicitly compute correlation functions and read off the anomalous dimension of the operators. The latter are given by logarithmic divergences that the irrelevant deformation induces. This will provide us with a direct method to derive the spectrum of the theory. I will compare this type of irrelevant deformation with the recently studied T\bar{T}-deformation of a CFT2, which can be thought of as a single-trace analog of the former.

 Soutenance de thèse et Mini-workshop on Topology in condensed matter Vendredi 7 septembre 2018, 9h30 LPTMS, Bâtiment 100, 15 Rue Georges Clemenceau, 91405 Orsay Kirill Plekhanov (Equipe Matière condensée) "Topological Floquet States, artificial gauge fields in strongly correlated quantum fluid" Abstract : In this thesis we study the topological aspects of condensed matter physics, that received a revolutionary development in the last decades. Topological states of matter are protected against perturbations and disorder, making them very promising in the context of quantum information. The interplay between topology and interactions in such systems is however far from being well understood, while the experimental realization is challenging. Thus, in this work we investigate such strongly correlated states of matter and explore new protocols to probe experimentally their properties. In order to do this, we use various both analytical and numerical techniques. First, we analyze the properties of an interacting bosonic version of the celebrated Haldane model – the model for the quantum anomalous Hall effect. We propose its quantum circuit implementation based on the application of periodic time-dependent perturbations – Floquet engineering. Continuing these ideas, we study the interacting bosonic version of the Kane-Mele model – the first model of a topological insulator. This model has a very rich phase diagram with an emergence of an effective frustrated magnetic model and a variety of symmetry broken spin states in the strongly interacting regime. Ultra-cold atoms or quantum circuits implementation of both Haldane and Kane-Mele bosonic models would allow for experimental probes of the exotic states we observed. Second, in order to deepen the perspectives of quantum circuit simulations of topological phases we analyze the strong coupling limit of the Su-Schrieffer-Heeger model and we test new experimental probes of its topology associated with the Zak phase. We also work on the out-of-equilibrium protocols to study bulk spectral properties of quantum systems and quantum phase transitions using a purification scheme which could be implemented both numerically and experimentally. La soutenance sera suivi d'un mini workshop : Mini-workshop on Topology in condensed matter -- 13:30 - 17:00 13:30-14:00: Walter Hofstetter 14:00-14:30: Titus Neupert 14:30-15:00 : Nathan Goldman 15:00-15:30: pause 15:30-16:00 : Guido Pupillo 16:00-16:30: Nicolas Regnault 16:30-17:00: Mark Oliver Goerbig

 Séminaire de Physique des ParticulesCPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Jeudi 6 septembre 2018 à 11hCPHT, Ecole Polytechnique, Salle de Conférence Louis Michel (Bât. 6) David Dudal (KU Leuven) BRST quantization in conjunction with the Gribov gauge xing ambiguity We review the Faddeev-Popov quantization procedure when applied to non-Abelian SU(N) gauge theories. We introduce the BRST symmetry of the gauge fixed action and briey discuss its relevance for establishing renormalizability, constructing a physical Fock space and recovering gauge invariant expectation values at the quantum level. All the above assumes a strict perturbative treatment. Unfortunately, once this domain is left, a new problem appears: multiple solutions to the gauge fixing condition spoil the mathematical raison d'^etre of the Faddeev-Popov procedure. This Gribov ambiguity, and more specically treating it, has a profound inuence on correlation functions beyond the perturbative (ultraviolet) regime. We discuss a possible way how it can be taken into account, modulo some simplications, in terms of a modifed effective action. We end by describing recent efforts to reconcile this new quantization procedure with BRST symmetry, given the latter's importance.

 Séminaire de Physique des ParticulesCPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Jeudi 28 juin 2018 à 11hCPHT, Ecole Polytechnique, Salle de Conférence Louis Michel (Bât. 6) Matthias Burkardt (New Mexico State University) Nucleon tomography Generalized parton distributions embody information on both the longitudinal momentum of the quarks as well as their transverse position and thus allow determining a 3-dimensional image of the nucleon. For transversely polarized quarks and or nucleons, the resulting transverse deformation of these images provides new insight on nucleon spin structure and spin-orbit correlations. Twist-3 GPDs provide additional information on the dependence of transverse forces on the impact parameter.

 Bi-séminaire CORDES Jeudi 7 juin 2018 CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel (Bât. 6) 10:30 Amir Kashani-Poor (LPTENS, Paris) Topological strings and 6d SCFTs The topological string is a simplified version of physical string theory. It is of interest because it computes the BPS spectrum of relevant string theory compactifications, but also because it shares structural properties of physical string theory. Dualities and symmetries which often must be argued for arduously in the physical string can often be verified by computation in the topological setting. The central observable of the theory is the topological string partition function Z_top. This quantity has an eerie habit of making surprise appearances in many areas of mathematical physics. Numerous techniques exist for its computation in various expansions in parameters of the theory, yet to date, no satisfactory closed form for this quantity is known. In this talk, after reviewing notions of topological string theory with an emphasis on the interplay between worldsheet and target space physics (one of the structural similarities between the physical and the topological string alluded to above), I will report on progress in computing Z_top in settings where it is related to enigmatic 6d theories.   11:45 Rob Leigh (University of Illinois, Urbanna)  String Zero Modes, T-duality, Vertex States and Entanglement In this talk, I will touch on a variety of topics related to the notion of edge modes. I’ll discuss their relevance in simple string theory settings, leading to an interpretation in terms of non-commutative geometry. This will lead into a discussion of topology change in Lorentzian quantum gravity, and relations to quantum entanglement.

 Séminaire de Physique des ParticulesCPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Mardi 20 février 2018 à 11h00 CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel (Bât. 6) Kasper Larsen (Southampton U.) Algebraic geometry applied to multi-loop scattering amplitudes/span>   The computation of two-loop amplitudes forms a current bottleneck to computing precisionlevel cross sections for LHC phenomenology. In this talk I will discuss several new methods for analytic evaluation of two-loop amplitudes, drawing inspiration from algebraic geometry and modern unitarity. More specifically, the methods involve efficient determination of a basis of integrals in terms of which the amplitude is decomposed; derivation of the integral identities needed to perform the decomposition; and evaluation of the basis integrals via differential equations. The first step of determining a basis of integrals has been implemented in the publicly available code Azurite which I will discuss. I will also discuss future implementations of the methods and their application to computing the two-loop five-gluon QCD amplitud

 Journée des thèses du CPhT Mardi 6 février 2018 à partir de 10h30 CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel

 Séminaire de Physique des ParticulesCPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Vendredi 15 décembre 2017 à 14h00 CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel Cédric Mezrag (INFN. Roma) Exploring the nucleon structure   Understanding the emergence of the nucleon structures in terms of QCD degrees of freedom, i.e. quarks and gluons, is one of the major challenges of hadron physics. Two main types of non-perturbative techniques have been developed to tackle this challenge, discretised ones using large computer simulations (LQCD), and continuum ones relying on Dyson-Schwinger equations (DSEs). The latter suggest for instance that dynamical diquarks are generated inside the nucleon, creating eective degrees of freedom. Since both LQCD and DSEs techniques can be used in order to compute local matrix elements related to the structures of the Nucleon through for instance Distributions Amplitudes (DAs), we will explore in this talk the possibility of understanding the nucleon structure in terms of dynamical degrees of freedom.

 Soutenance de thèse au CPHT : Alain Marx (Equipe Plasmas magnétisés) "Deux étapes majeures pour le développement du code XTOR : parallélisation poussée et géométrie à frontière libre" Jeudi 23 novembre, 14h, Amphi Curie Résumé de la thèse : Le code XTOR-2F simule la dynamique 3D des instabilités MHD bi-fluides de plasmas de tokamaks. La première partie de la thèse a été consacrée à la parallélisation du code XTOR-2F. Le code a été parallélisé significativement malgré la représentation pseudo-spectrale pour les deux directions angulaires, la raideur des équations résolues et l’utilisation d’une décomposition LU exacte afin d’inverser le préconditionneur physique. Le temps d’exécution de la version parallèle est un ordre de grandeur plus petit que la version séquentielle sur un maillage basse résolution. L’accélération croît ensuite avec la taille du maillage. La parallélisation permet également de réaliser des simulations avec des maillages plus grands, autrefois non réalisables par la limitation du stockage en RAM. La seconde partie de la thèse a été consacrée au développement d’une version du code permettant de réaliser des simulations en géométrie à frontière libre, s’approchant de la géométrie des tokamaks expérimentaux de grande taille. Les conditions initiales sont fournies par le code d’équilibre CHEASE à l’intérieur du plasma. A l’extérieur du plasma, la solution a été étendue en ajustant le potentiel magnétique avec un ensemble de bobines magnétiques poloïdales externes. Les conditions de bord utilisent des fonctions de Green afin de calculer une matrice de transfert permettant de relier les composantes tangentes et normales du champ magnétique externe à la coque avec la solution interne. Ceci permet de modéliser une coque résistive fine. Cette nouvelle version élargit le domaine d’investigation de XTOR-2F, autrefois restreint aux instabilités internes, aux instabilités externes. Le comportement linéaire du code est validé sur deux familles d’instabilités, les modes axisymétriques n = 0 et les kinks externes n = 1 / m = 2. Afin de valider le comportement non linéaire, des simulations en MHD résistive de modes tearing à bêta nul évoluant vers un état stationnaire ont été réalisées

 Soutenance de thèse au CPHT : Alexander Efremov (Equipe Physique Mathématique) "Renormalization of SU(2) Yang-Mills theory with flow equations" Mercredi 27 septembre, 15h, Salle de Conférences du CPhT, Bâtiment 6 Résumé de la thèse : Le problème de la renormalisation perturbative de la théorie de la SU (2) Yang-Mills est étudié dans l'espace euclidien à quatre dimensions dans la jauge de Lorenz. L'analyse est basée sur les équations du flot de groupe de renormalisation. Il s'agit d'une approche unifiée qui permet d'étudier une large gamme de théories sans recourir aux diagrammes de Feynman. Les équations du flot nous permettent de construire toutes les fonctions irréductibles de la théorie, en utilisant uniquement les conditions de renormalisation. Une partie importante du travail consiste à établir des bornes supérieures dans l'espace des impulsions pour toutes les fonctions irréductibles à tous les ordres en boucle. Ces bornes ont une interprétation graphique très naturelle sous forme d'arbres. Afin de définir correctement les fonctions irréductibles, il faut introduire des cut-offs ultraviolet et infrarouge. Mais cette régularisation brise l'invariance BRST. Il est donc essentiel de prouver à tous les ordres en boucle que la construction des fonctions irréductibles puisse se faire de manière que l'invariance BRST soit rétablie dans la limite où le cut-off UV va vers l'infini. En outre, un effort important est fourni pour établir un schéma de renormalisation qui permet d'imposer des conditions de renormalisation physiques explicites.

 Séminaire de Physique des ParticulesCPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Jeudi 28 Septembre 2017 CPHT, Ecole Polytechnique, Salle de Conférence du bât. 6 Rainer Stiele (Lyon, IPN et Frnakfurt U.) Phase structure and thermodynamics of strongly-interacting matter   Currently, large effort is undertaken, experimentally in heavy ion collisions and theoretically doing simulations on supercomputers, to explore the state of matter under the extreme conditions of the largest temperatures and densities in the universe. Effective models, such as Polyakov-loop-extended chiral models, which capture the main properties of the strong interaction, i.e. the creation of con- stituent quark masses and connement, play the role of an important guidance that allow access at all temperature and density domains. Results of such a model, the Polyakov-loop-extended Quark-Meson truncation of QCD, for the phase diagram of strongly-interacting matter are presented and it will be discussed how constraints from the high-energy domain (lattice calculations) as well as low energy domain (astrophysics measurements on compact stars) can contribute to pin it down more precisely. The importance of including the quark backreaction on the gauge eld dynamics is demonstrated and its impact on the structure of the phase diagram and on the surface tension for nucleation in a rst order transition region discussed. Finally, the necessity to improve the description of the gauge part of the strong interaction with phenomenological Polyakov-loop potentials will be motivated and current ways to improve will be outlined.

 Soutenance de thèse au CPHT : Pascal Delange (Equipe Matière condensée) "Physique à N corps des électrons dans les composes de métaux de transition et de terre rares : structure électronique, propriétés magnétiques et défauts cristallins ponctuels à partir des premiers principes" Vendredi 29 septembre, 11h, Amphi Becquerel, Ecole Polytechnique Résumé de la thèse : Les propriétés structurelles, magnétiques et de conduction des matériaux sont déterminées par le comportement des électrons qui lient leurs atomes. Certaines des plus importantes avancées technologiques du 20e siècle ont eu lieu dans le domaine des semi-conducteurs, dans lesquels les électrons se comportent comme un gaz peu dense interagissant faiblement. En revanche, les oxydes sont des matériaux prometteurs pour les applications technologiques  à venir. Dans les oxydes de métaux de transition ou de terres rares, ainsi que dans certains métaux purs et alliages, la répulsion entre électrons peut donner lieu à des propriétés exotiques et à des transitions de phase. Dans cette thèse, nous avons développé et utilisé des méthodes partant des “premiers principes” de la physique pour évaluer le comportement d’électrons en interaction et les propriétés physiques qui en découlent. Nous avons appliqué ces outils à plusieurs matériaux, en particulier le fer, le dioxyde de vanadium et les aimants permanents.

 Soutenance de thèse au CPHT : Pierre Chopin  (Equipe Plasmas magnétisés) "Modélisation à grande échelle pour les phénomènes éruptifs" Vendredi 29 septembre, 14h, Amphi Bécquerel, Ecole Polytechnique Résumé de la thèse : Cette thèse a pour objet la modélisation du champ magnétique de la couronne solaire à l’aide du code de reconstruction non-linéaire XTRAPOLS, avec une attention particulière pour les phénomènes éruptifs. Le caractère novateur des études menées porte sur l’aspect sphérique global de la méthode. Trois études principales de cas sont présentées dans cette thèse. La première concerne les évènements éruptifs de février 2011, géoeffectif, faisant figurer une région active étendue. Nous mettons en évidence plusieurs structures de tubes de flux torsadés, et caractérisons leur lien avec les structures à grande échelle. La deuxième concerne les évènements du 3 et 4 août 2011. Plusieurs régions actives sont présentes sur le disque solaire, et deux d’entre elles présentent une activité éruptive importante. Là encore, nous mettons en évidence des tubes de flux torsadés dans chacune de ces deux régions active, et mettons en lumière les liens topologiques qui existent entre elles. La Troisième concerne une étude faite dans le cadre d’un groupe NLFFF, pour l’étude de la modélisation non- linéaire globale de la couronne. La date correspondant à la reconstruction est celle de l’éclipse totale de soleil du 20 mars 2015. Nous discutons ici de l’impact de différents types de données et de modèles utilisés, et soulignons l’importance de la cohérence temporelle et de l’inclusion du courant dans les régions actives. Les travaux présentés dans cette thèse ont donc permis de caractériser l’en- vironnement global des régions actives éruptives et d’étudier les liens entre les éléments à différentes échelles. Nous présentons en guise d’ouverture différente méthode pour étendre la modélisation au-delà de la surface source.

 Colloquium CPHT - Ecole polytechnique Mardi 12 septembre à 14h CPhT, Ecole Polytechnique, Salle de Conférence du bât. 6 Eric Akkermans, Universite Technion, Israel(bureau au CPHT, aile zero 10.14) https://phys.technion.ac.il/en/people/faculty?view=person&id=45 Observing a Scale Anomaly in Graphene : a Universal Quantum PhaseTransition Abstract : Scale invariance is a common property of our everyday environment. Its breaking gives rise to less common but beautiful structures like fractals. At the quantum level, breaking of continuous scale invariance is a remarkable exemple of quantum phase transition also known as scale anomaly. The general features of this transition will be presented at an elementary quantum mechanics level. Then, we will show recent experimental evidence of this transition in graphene.

 Soutenance de thèse : Vendredi 8 septembre à 14h Amphi Becquerel, Ecole Polytechnique Loïc Herviou "Phases topologiques et Fermions de Majoran" Dans cette thèse, nous étudions d'un point de vue théorique différents aspects de la matière topologique. Ces systèmes présentent des propriétés résistantes aux éventuelles perturbations grâce à une topologie non-triviale de leur structure de bandes. Des excitations exotiques, par exemple des fermions de Majorana, peuvent apparaitre à leurs bords. L'étude des marqueurs d'intrication a été fondamentale dans la compréhension de ces systèmes, et des phases libres en général. Il est cependant difficile de les mesurer. Les fluctuations de charge bipartites, permettant une mesure faible de l'intrication, ont été proposées comme alternative. Nous généralisons les précédents travaux sur les Liquides de Luttinger à des familles génériques de supraconducteurs et isolants topologiques en une et deux dimensions. Les fluctuations suivent une loi de volume, liée à l'Information Quantique de Fisher et non-analytique aux transitions de phase. Leurs points critiques sont caractérisés par des coefficients universels, qui révèlent leur topologie. Dans un second temps, nous considérons des systèmes en interactions. Certaines des signatures des transitions topologiques survivent dans les supraconducteurs topologiques. Nous étudions ensuite le diagramme de phase de deux fils supraconducteurs couplés par une interaction Coulombienne, présentant des phases exotiques grâce à la compétition avec la supraconductivité non-conventionnelle. Des courants orbitaux brisant spontanément la symétrie de renversement du temps peuvent apparaître, ainsi qu'une phase de fermions libres, extension de deux chaînes de Majorana critiques. Enfin, nous nous intéressons aux effets des fermions de Majorana sur le transport électronique. Nous étudions un îlot supraconducteur où plusieurs de ces fermions existent, pouvant être l'un des composants élémentaires d'un éventuel ordinateur quantique. Ces impuretés changent les statistiques des porteurs de charges, menant à une fractionalisation robuste de la conductance. Nous étendons les études précédentes au cas où le nombre d'électrons dans la boîte peut fluctuer, et montrons l'équivalence de ce problème avec le modèle Kondo à plusieurs canaux. Nous réinterprétons alors ce modèle en terme du déplacement d'une particule dans un réseau fictif dissipatif. Ce travail a été réalisé en cotutelle au Centre de Physique Théorique et au Laboratoire Pierre Aigrain (ENS) sous la direction de Karyn Le Hur et Christophe Mora.

 Séminaire de Physique des Particules CPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Jeudi 6 juillet 2017 CPHT, Ecole Polytechnique, Salle de Conférence du bât. 6 Bo-Wen Xiao (CCNU, Wuhan and Hua-Zhong Normal U.) Inclusive dijet productions in pp and AA collisions In this talk, I will rst discuss the systematic calculation of dijet angular correlation and dijet asymmetries in pp collisions. Then, using the above pp results as a baseline, we can further put in the quark-gluon plasma medium effect and extract the corresponding medium transport coefficient at RHIC and the LHC. The dijet processes can serve as direct probes of QGP medium at NLO accuracy and play important roles at RHIC and the LHC. In the end, I will also discuss the further development of jet physics in heavy ion physics.

 Séance de présentation des stages de master Mercredi 21 juin 2017 Ecole Polytechnique, CPHT, Aile zéro, Salle de Conférence Le laboratoire organise une séance de présentation des stages de master le mercredi 21 juin, à 14h, dans la salle de conférence de l’aile 0. Chaque étudiant disposera de dix minutes pour présenter son sujet de stage de manière non technique et compréhensible par des non spécialistes. Cette séance sera suivie d’une collation vers 16h30. Programme : - R. CAMPOS DE CARVALHO (C. Lorcé)Lorentz invariance and n-independence - B. DAGALLIER (J.-R. Chazottes)Quasicrystals: properties and theoretical application - J. DOUÇOT (M. Petropoulos)The Hawking effect and the black hole information problem - C. FLEMING et T. COUDARCHET (H. Partouche)Quantum stability of flat spacetime: a superstring point of view - G. GIACALONE (C. Marquet)Phenomenology of strong interaction at high energy - M. HUMBERT (M. Petropoulos)Holographic reconstruction in higher dimensions - T. LESAFFRE (S. Billard)Influence du régime de reproduction sur l'évolution de l'investissement reproducteur chez les Angiospermes - A. LI (C. Lorcé)Angular momentum in the scalar diquark model - S. POEGEL (G. Bossard)Hidden Symmetries in Supergravity - C. SHI (G. Bossard)Gauge and gravitational anomalies in Standard Model - F. YANG (Karyn Le Hur)Topological Phases and Majorana Fermions - H. YAO (Laurent SANCHEZ-PALENCIA)The Tan contact for 1D Bose gases

 Séminaire de Physique des Particules CPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Jeudi 22 juin2017 IPN, Orsay, Bât. 100, Salle A201 Shayan Ghosh (Indian Institute of Science, Bangalore) Analytic solutions to massive two-loop sunset diagrams, and applications to Chiral Perturbation Theory In this talk, we begin by showing how it is possible to obtain full analytic results for the two-loop three distinct mass scale sunset diagrams that appear in the expressions for the masses and decay constants of the pion, kaon and eta particles in two-loop SU(3) chiral perturbation theory. We then talk about two applications of these results: a) how it allows one to obtain small quark mass ratios to arbitrarily high powers, and b) how it allows one to make ts to lattice data to extract greater information about low energy constants. We then change track and discuss in more detail the Mellin- Barnes method used in our calculations, and demonstrate how this method can be extended using analytic continuation to obtain results for Feynman diagrams whose mass value parameters are such that it is impossible to use a direct calculation. We show how such methods of analytic continuation can also be helpful in contexts where a direct calculation does yield results, and thus set the stage for more widespread application of this technique.

 Séminaire de Physique des Particules CPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Vendredi 28 avril 2017 (Attention : Jour inhabituel!) Ecole Polytechnique, CPhT, bât. 6, Salle de Conférence Zsolt Szép (Eötvös University, Budapest) Thermodynamics of the vector meson extended quark-meson model We investigate the effects of (axial)vector mesons on the chiral phase transition of the model containing 2+1 constituent quarks and Polyakov-loop degrees of freedom. A x2 minimization procedure is used to parameterize the model based on tree-level decay widths and vacuum scalar and pseudoscalar curvature masses which includes the vacuum and thermal contribution of the constituent quarks. The pressure and the derived thermodynamical observables determined from it at nite temperature T and chemical potential using a simple approximation for the grand potential are compared to lattice results. The best parametrization of the model allows for the existence of the critical end point (CEP) of the T phase diagram.

 Colloquium du CPHT, Ecole Polytechnique Mercredi 15 mars 2017 à 15h00 Salle de séminaire du CPhT, bâtiment 6 Sylvain Carrozza (Perimeter Institute, Waterloo Canada) Quantum fields with tensorial locality Abstract: In recent years, generalizations of matrix models known as Tensor Models and Group Field Theories have been developed into a consistent formalism. The common feature of these field theories is an abstract notion of locality, known as tensorial locality, which encodes the combinatorial structure of the elementary field interactions. It has initially been introduced in the context of quantum gravity, where indeed the absence of a non-dynamical background space-time renders the standard notion of locality inoperative. I will provide an overview of this approach, focusing on general features of the phase diagrams of tensorial theories, and of their possible applications to quantum gravity and statistical physics. I will also discuss a new range of applications at the crossroad between condensed matter and the AdS/CFT correspondence: following a recent insight from Witten, tensorial techniques are being taken advantage of to investigate the properties of so-called Sachdev-Ye-Kitaev models of randomly interacting fermions.

 Colloquium du CPHT, Ecole Polytechnique Vendredi 10 mars 2017 à 14h Salle de séminaire du CPHT, bâtiment 6 Leonardo Mazza(Ecole Normale Supérieure, Paris) Towards the quantum-Hall-effect with ultra-cold atoms and synthetic dimensions Abstract: Synthetic ladders pierced by a magnetic field realized with one-dimensional alkaline-earth(-like) gases represent a promising environment for the investigation of many-body quantum physics with ultracold atoms. A fundamental question is whether these setups can give access to pristine two-dimensional phenomena, such as the fractional quantum Hall effect, and how. I discuss the existence of a hierarchy of fractional insulating and conducting states by means of both analytical techniques (bosonization) and numerical methods (density-matrix renormalization group algorithm). I show that such states can be exploited for constructing a topological Thouless pump where the charge transported after one cycle is quantized to fractional values and demonstrate this behavior with a full many-body time-dependent calculation. I conclude by presenting numerical signatures of bosonic and fermionic Laughlin-like states that can be observed in these setups. 1 - S. Barbarino, L. Taddia, D. Rossini, L. Mazza, R. Fazio, Nat. Commun. 6, 8134 (2015) 2 - S. Barbarino, L. Taddia, D. Rossini, L. Mazza, R. Fazio, New J. Phys. 18, 035010 (2016) 3 - L. Taddia, E. Cornfeld, D. Rossini, L. Mazza, E. Sela, R. Fazio, arXiv:1607.07842 (2016) 4 - M. Calvanese Strinati, E. Cornfeld, D. Rossini, S. Barbarino, M. Dalmonte, R. Fazio, E. Sela, L. Mazza, arXiv:1612.06682 (2016)

 Colloquium du CPHT, Ecole Polytechnique Vendredi 3 mars 2017 à 11h Salle de séminaire du CPHT, bâtiment 6 Charles Grenier (Ecole Normale Supérieure de Lyon) Mesoscopic transport with ultracold atoms Abstract: The last years have seen the emergence of a new trend in cold atoms experiments towards the simulation of quantum transport. In this talk, I will show how one can use cold gases to simulate mesoscopic devices, and how adding a cold atom flavour to a transport setup can help pushing further our understanding of low dimensional structures. In particular here, I will focus on the evolution of particle and spin conductances as functions of the interaction strength. S. Krinner et al., Proceedings of the National Academy of Sciences 113 (29), 8144-8149

 Séminaire de Physique des Particules CPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Mardi 28 février 2017 à 11h00(Attention : Jour inhabituel!) Ecole Polytechnique, CPHT, bât. 6, Salle de Conférence Daniel Kroff (IFT-Unesp, Sao Paulo) The Linde problem on R2 x S1 x S1 Thermal eld theory provides the natural framework to describe the thermodynamic properties and to study phase transitions of systems describe by quantum eld theories, in particular, the quark-gluon plasma. However, its perturbative realization faces important technical difficulties whenever massless bosons are considered, due to divergences in the IR sector. After briefly reviewing these IR divergences in thermal eld theory, and especially the Linde problem, we analyze the IR behavior of Yang-Mills theory in a Torus -- R2 x S1 x S1 -- and show that, in this geometry, any perturbative calculation is expected to break-down already at O(g2).

 Colloquium du CPHT, Ecole Polytechnique Jeudi 23 février 2017 à 11h Salle de séminaire du CPHT, bâtiment 6 Jamal Jalilian-Marian"Visiting Professor"  au Centre de Physique Théorique, programme "Jean d'Alembert" de l'Université Paris-Saclay An introduction to high energy scattering in QCD Abstract: After a brief introduction to Quantum ChromoDynamics (QCD), the fundamental theory of strong interactions, we consider scattering of hadrons (protons and neutrons) and nuclei at very high energies. It is shown that scattering cross sections at high energy are dominated by components of the hadron/nucleus wave function that contain a large number of soft partons (gluons and sea quarks carrying a small fraction x of the hadron energy). An effective action, known as Color Glass Condensate, is proposed that describes the dynamics of this many body system of gluons at small x. Applications to particle production at the Large Hadron Collider (LHC), Relativistic Heavy Ion Collider (RHIC) and the proposed Electron Ion Collider (EIC) will be discussed in detail and connections to other branches of physics, cosmic rays, high energy neutrinos, Quark Gluon Plasma and statistical physics will be elucidated.

 Colloquium du CPHT, Ecole Polytechnique Jeudi 2 février 2017 à 11h Salle de séminaire du CPHT, bâtiment 6 Jeffrey BrownUniversité de Louisiane, Baton Rouge et Centre de Physique Théorique, Ecole polytechnique Modeling ultrashort laser pulses in gases Abstract: The interaction of short, intense (10^14 W/cm^2) laser pulses with atomic and molecular gases produces a wide range of interesting nonlinear optical phenomena.  Accurately modeling how microscopic quantum processes give rise to macroscopic optical properties in a computationally feasible manner is challenging. For determining which "ingredients" are necessary in a model to capture the most dominant quantum processes, we investigated the utility of exactly solvable, quantum-based laser-matter interaction models. From this new understanding, we have developed a novel laser-matter interaction model based on Stark resonant states, which provides an accurate and computationally efficient method of representing the nonlinear response of a gaseous medium.

 Colloquium du CPHT, Ecole Polytechnique Jeudi 12 janvier 2017 à 11h Salle de séminaire du CPHT, bâtiment 6 Timothée Nicolas SPC-EPFL, Lausanne, Suisse MHD instabilities : from tokamaks to stellarators Abstract: We will explore different aspects of magnetohydrodynamic (MHD) instabilities in tokamaks and stellarators. Both devices require a helical magnetic field to efficiently confine a hot fusion plasma in a torus. External coils generate a main field of the order of 2-4 T. Tokamaks generate the second component of the field using a large electric current in the plasma itself. Stellarators however generate all the field using only external coils. This gives rise to different kinds of instabilities in both devices, mainly current driven in tokamaks, mainly pressure driven (Rayleigh-Taylor like) in stellarators. We will review some theoretical issues related to the MHD stability in both tokamaks and stellarators. We will see why they are crucial in practice, in view of future experiments such as ITER. We will also try to give a taste of the numerical challenge faced by whoever tries to simulate the complex nonlinear behavior of such plasmas.

 Séminaire de Physique des Particules CPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay jeudi 15 décembre 2016 à 11h00 Ecole Polytechnique, CPHT, bât. 6, Salle de Conférence Jamal Jalilian-Marian (CUNY) Light-front quantization methods: from QED to QCDWe utilize spinor helicity techniques to calculate the production of three polarized partons in DIS at small x using the Color Glass Condensate formalism. We show that the azimuthal angular correlations between the produced partons is a sensitive probe of the dynamics of the proton/nucleus wavefunction at small x and gluon saturation. Extensions of the results to MPI as well as ultra-peripheral heavy-ion collisions will be discussed. We will nish by speculating on possible applications of the methods/results to energy loss phenomena in head-on (central) high-energy heavy-ion collisions.

 Sophie Chauvin Soutiendra publiquement ses travaux de thèse intitulés "Etude des cobaltates fortement dopés par méthodes premiers principes et théorie du champ moyen dynamique étendue" Soutenance prévue le mercredi 14 décembre 2016 à 14h00 Lieu :   Amphi Monge, Ecole Polytechnique, Route de Saclay, 91128 Palaiseau Résumé

 Soutenance de thèse / Physique des Plasmas jeudi 24 novembre 2016 à 14h00 Amphi Cauchy, Ecole Polytechnique, Route de Saclay, 91128 Palaiseau Jae Heon AHN Impact des instabilités MHD bi-fluide sur le transport d’impuretés dans les plasmas de tokamaks Les performances des plasmas de fusion confinés magnétiquement peuvent être dégradées par l'accumulation d'impuretés. Plus particulièrement, les impuretés lourdes accumulées au centre du plasma diluent les réactifs, et peuvent aussi conduire à un collapse radiatif du plasma par de fortes pertes par rayonnement. La compréhension du transport des impuretés lourdes produites lors de l'interaction plasma-paroi est donc devenue cruciale. Le coeur du plasma est sujet à une instabilité magnétohydrodynamique (MHD) appelée ‘kink interne’, conduisant à des oscillations de relaxation nommées ‘dents de scie’. Les dents de scie entraînent une relaxation périodique de densité et de température dans le coeur du plasma, et affectent significativement le transport radial. Notamment, les particules et la chaleur sont redistribuées pendant un crash dont la durée est très courte par rapport au temps de confinement. En l'absence des instabilités MHD, le transport des impuretés est porté par les collisions (transport néoclassique) et la turbulence. Il est établi que le transport néoclassique est important pour les impuretés lourdes dans la région centrale du plasma de tokamak. Cependant, des mesures expérimentales du tokamak ASDEX-Upgrade montrent que la dynamique des impuretés en présence des dents de scie est différente des prédictions faites par les codes de transport. Dans cette thèse, l'outil numérique utilisé pour simuler les dents de scie est le code XTOR-2F, qui est un code non-linéaire tridimensionnel résolvant les équations de la MHD. Les équations fluides modélisant le transport des impuretés dans un régime de collisionalité élevée (Pfirsch-Schlüter) ont été implémentées et couplées avec l'ensemble des équations de la MHD bi-fluide. Les simulations montrent que les profils de densité d'impuretés sont affectés par les dents de scie, en accord avec les observations expérimentales. Ceci résulte d'une compétition entre processus néoclassiques et relaxations dues aux dents de scie.

 Séminaire de Physique des Particules CPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay jeudi 24 novembre 2016 à 11h00 Ecole Polytechnique, CPHT, Salle des Conférences Luca Mantovani (Université de Pavie) Light-front quantization methods: from QED to QCD Abstract : I present an overview of the basic concepts concerning the formalism of light-front quantization for field theories, usually applied in the framework of hadron physics. I describe some applications in the field of Quantum Electrodynamics, focusing in particular on the Transverse- Momentum Dependent distribution functions (TMDs) for the case of a dressed electron, and discuss some subtleties related to the features of the gauge-field propagator in light-cone gauge. I also give a hint about an application in the field of Quantum Chromodynamics, concerning the nucleon’s energy-momentum tensor.

 Séminaire général du Centre de Physique Théorique Vendredi 14 octobre à 14h00 Salle de Conférence bat. 6, Centre de Physique Théorique, Ecole Polytechnique Laurent Sanchez-Palencia Laboratoire Charles Fabry (CNRS, Institut d'Optique, Univ Paris-Saclay) Quantum Simulation with Ultracold Atoms: A Theoretical Perspective Within the very last decade, the fantastic development of quantum technologies at the frontier of condensed matter, atomic physics, and photonics has open a new window on the quantum world. While conceived by Richard Feynman more than thirty years ago to treat problems that can hardly be solved by classical computers, quantum simulators are now becoming a reality. In this respect, ultracold atoms offer a fantatic platform for they are extremely well controlled and versatile systems. Proof of concept of quantum simulation has already been reported in a number of milestone works. They now pave the way to simulation of strongly-correlated quantum systems relevant to many areas, including condensed-matter and high-energy physics.In this presentation, we will give a general introduction to ultracold atoms and quantum simulators. Various landmark advances will be presented with the aim of providing a general overview of present-day possibilities and immediate perspectives. We will then discuss recent results on disordered quantum systems, quantum phase transitions, and out-of-equilibrium dynamics in correlated systems, which form the core of our activites. Short and mid-term perspectives of our work will also be briefly discussed.

 Séminaire X-CPHT - IPN-Théorie Jeudi 22 Septembre 2016 à 11h Salle de Conférence bat. 6, Centre de Physique Théorique, Ecole Polytechnique Amir Rezaeian (Santa Maria Univ., Valparaiso & CCTVal) Diffractive dijet production in the CGC Diffractive dijet production in the CGC I will talk about exclusive dijet production in coherent diffractive processes in deep inelastic scattering and real (and virtual) photon-hadron collisions in the Color Glass Condensate for malism. I show that the diffractive dijet cross section is sensitive to the color-dipole orientation in the transverse plane, and is a good probe of possible correlations between the dipole transverse separation vector and the dipole impact parameter. I also show that the t-distribution of diffractive dijet photo-production off a proton target exhibits a diptype structure in the saturation leads to stronger azimuthal correlations between the jets.

 Séminaire : phases topologiques et Fermions de Weyl en matière condensée Mercredi 14 Septembre 2016 à 11h00 Salle de séminaire du CPHT, batiment 6 Ion Garate, professeur à Sherbrooke (Canada, Quebec) Magnetic-field-induced effective phonon charges in Weyl semimetals Abstract: A recent major development in the field of topological materials has been the realization that topological phases occur in three dimensional semimetals that host Weyl nodes. The experimental discovery of Weyl nodes in TaAs has sparked an intense interest in this class of materials, generally called Weyl semimetals (WSM).  A key topological phenomenon in WSM is the chiral anomaly, by which a collinear electric and magnetic field induce a transfer of electrons between Weyl nodes of opposite chirality. The chiral anomaly manisfests itself through an unsual electromagnetic response, consisting of a large negative magnetoresistance, anomalous Hall and chiral magnetic effects and nonlocal electrical transport. So far, experimental efforts to detect the chiral anomaly in WSM have been focused on electrical transport. However, there is a strong interest in developing new experimental probes that could offer complementary understanding of this phenomenon. In this talk, I will discuss how the chiral anomaly impacts phonons in WSM. In WSM belonging to certain symmetry classes, a static and uniform magnetic field induces an effective phonon charge that contains a peculiar resonance. I will list some physical consequences of this effect, such as magnetic-field-induced infrared activity, magnetic-field-induced anomalies in the phonon dispersion, and resonant Raman scattering.

 Séminaire de Physique des ParticulesCPHT-Ecole Polytechnique et Groupe Théorie IPN Orsay Jeudi 28 Septembre 2017 CPHT, Ecole Polytechnique, Salle de Conférence du bât. 6 Rainer Stiele (Lyon, IPN et Frnakfurt U.) Phase structure and thermodynamics of strongly-interacting matter   Currently, large effort is undertaken, experimentally in heavy ion collisions and theoretically doing simulations on supercomputers, to explore the state of matter under the extreme conditions of the largest temperatures and densities in the universe. Effective models, such as Polyakov-loop-extended chiral models, which capture the main properties of the strong interaction, i.e. the creation of con- stituent quark masses and connement, play the role of an important guidance that allow access at all temperature and density domains. Results of such a model, the Polyakov-loop-extended Quark-Meson truncation of QCD, for the phase diagram of strongly-interacting matter are presented and it will be discussed how constraints from the high-energy domain (lattice calculations) as well as low energy domain (astrophysics measurements on compact stars) can contribute to pin it down more precisely. The importance of including the quark backreaction on the gauge eld dynamics is demonstrated and its impact on the structure of the phase diagram and on the surface tension for nucleation in a rst order transition region discussed. Finally, the necessity to improve the description of the gauge part of the strong interaction with phenomenological Polyakov-loop potentials will be motivated and current ways to improve will be outlined.

 Séminaire  Physique Mathématique CPHT, Ecole Polytechnique, Salle de Conférence Louis Michel Mercredi 11 mars 14:00-15:00 : Bart van Ginkel Title: Hydrodynamic limit of the Symmetric Exclusion Process on compact Riemannian manifolds. Abstract: In this talk I will first explain the concept of the hydrodynamic limit of an interacting particle system. The idea is that one wants to show that when both space and time are rescaled (appropriately), the limiting densities of particles satisfy some PDE. This will be illustrated with the Symmetric Exclusion Process. Then we move this basic particle system to a hard context: Riemannian manifolds. I will highlight which challenges arise in the curved setting and how we deal with them. Joint work with Frank Redig. 15:00-16:00 : Rik Versendaal Title: Large deviations for geodesic random walks. Abstract: The theory of large deviations is concerned with the limiting behaviour on the exponential scale of a sequence of random variables. A fundamental result is Cramér’s theorem, which states that the empirical mean of a sequence of i.i.d. random variables satisfies a so called large deviations principle. Mogulskii’s theorem is concerned with the corresponding path space large deviations. To study the analogue of these theorems for a Riemannian manifold, we introduce a generalization of random walks to a manifold, called geodesic random walks. We present the analogues of Cramér’s and Mogulskii’s theorem for geodesic random walks and write down the rate function for these large deviations principles.

 Séminaire des cordes le vendredi 8 octobre 2021 à 15h00 au CPHT, Salle de conférence Louis Michel Anastasios Petkou "On scale, conformal and Weyl invariance in QFT" Abstract: Scale, conformal and Weyl invariance play a central role in Quantum Field Theories, and they are omnipresent in AdS/CFT correspondence. Through various examples I will review various issues and possible misconceptions regarding the interrelationships between these three important notions and connect them to some recent investigations.