String Theory
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Coordinator: Marios Petropoulos

Permanent staff
Guillaume Bossard
Emilian Dudas
Blaise Goutéraux
Hervé Partouche
Andrea Puhm

PhD students
Gabriele Casagrande
Victor Franken
Silvia Georgescu
Adrien Loty
Yorgo Pano
David Rivera Betancour
Filippo Sottovia
Matthieu Vilatte

Postdocs
Daniel Brattan
Sangmin Choi
Blagoje Oblak
David Ramirez
Mikel Sanchez Garitaonandia
Ashish Shukla
Marija Tomašević
Emilio Trevisani
Vaios Ziogas
Research activities
News
AdS/CMT seminar on Monday September 26th at 11am at CPHT, Conference room Louis Michel Daniel Arean (Universidad Autonoma de Madrid) "NonHermitian Holography" Abstract: The formulation and study of nonHermitian PTsymmetric 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 nonHermitian QFT, discuss its main features, and hopefully open up a discussion on future nonHermitian 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 largeorder 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 largeorder behaviour. Singulants obey simple equations of motion and govern the spacetime dependence of the largeorder behaviour of onshell constitutive relations.

AdS/CMT seminar Monday May 23rd, 2022 at 11am at CPHT, room Louis Michel Kamran Behnia (ESPCI, France) "On the dynamic distinguishability of nodal quasiparticles in overdoped cuprates" Abstract: La$_{1.67}$Sr$_{0.33}$CuO$_4$ is not a superconductor and its resistivity follows a purely T$^2$ temperature dependence at very low temperatures. La$_{1.71}$Sr$_{0.29}$CuO$_4$, on the other hand, has a superconducting ground state together with a TLinear term in its resistivity. The concomitant emergence of these two features below a critical doping is mystifying. Here, I begin by noticing that the electronelectron collision rate in the Fermi liquid above the doping threshold is unusually large. Therefore, the scattering time of nodal quasiparticles is close to the threshold for dynamic indistinguishibality, which is documented in liquid $^3$He at its zerotemperature melting pressure. Failing this requirement of FermiDirac statistics will exclude nodal electrons from the Fermi sea. Becoming classical, they will scatter other carriers within a phase space growing linearly with temperature. 
String theory seminar on Wednesday 18th 2022 at 14pm at CPHT, Conference room Jean Lascoux (Aile 0) Marc Geille (ANS 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.

AdS/CMT seminar Monday May 16th, 2022 at 11am at CPHT, room Louis Michel Saso Grozdanov (University Edinburg, UK) "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 'poleskipping' 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 Monday May 9th, 2022 at 11am at CPHT, room Louis Michel Nick Poovuttikul (Durham University, UK) " Anomaly “induce” transport in 2+1 dimensional QFT" Abstract: It is wellknown 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 higherform symmetry, highergroup symmetry and ’t Hooft anomaly captured in characteristic class beyond ChernSimons term. 
Séminaires des Cordes 11h  11h45 12h  12h45 
Aspects of gravity, mathematics and physics Cette conférence est organisée par le Centre de Mathématiques Laurent Schwartz et le Centre de Physique Théorique de Polytechnique. Orateurs Nicolas Besset (Paris Saclay) Guillaume Bossard (Polytechnique) Organisateurs Dietrich Häfner (UGA), Cécile Huneau (Polytechnique), Karim Noui (Paris Saclay), Marios Petropoulos (Polytechnique) Inscription obligatoire ici Lien vers l'affiche ici 
AdS/CMT seminar le mardi 14 décembre 2021 à 11h00 au CPHT, Salle de conférence Louis Michel Richard Davison (HeriotWatt University, Scotland) "Chaos and poleskipping in rotating black holes" Abstract: Outoftimeordered 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 'poleskipping' 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 KerrAdS 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 lowenergy 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 pseudospontaneous 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 Drudelike peak. In this scenario we show the validity of a universal relation between the phase relaxation rate, the mass of the pseudoGoldstone and the Goldstone diffusivity. 
Séminaire des cordes le jeudi 9 décembre 2021 à 16h00 sur Zoom Anomalies and Emergent Symmetries on the Lattice and in the Continuum 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. 
Séminaire des cordes le lundi 22 novembre 2021 à 11h00 au CPHT, Salle de conférence Louis Michel ChernSimons supergravity and black holes with unbroken supersymmetries We study particular supersymmetric extension of EinsteinGaussBonnet AdS gravity in five dimensions. The theory admits black hole solutions with nontrivial 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 threedimensional BTZ geometries.
Conformal renormalization in AdS gravity We present evidence that the renormalization of EinsteinAdS 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 EinsteinAdS action is naturally endowed with the correct counterterms. 
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. 
Andrea Puhm sur France Culture le 16 février 2021 Andrea Puhm, chargée de recherche au Centre de Physique Théorique a été invitée à parler du paradoxe de l'information des trous noirs dans l'émission " La méthode scientifique" sur France ulture le 16 février 2021. En savoir plus ici. 
Postdoctoral position(s) ERC "Hydrodynamics, Holography and stronglycoupled Quantum Matter" at the Center for Theoretical Physics, Ecole Polytechnique Contact : Blaise Goutéraux Dates 
Postdoctoral Position(s) ERC Starting Grant 'Information Encoding in Quantum Gravity and the Black Hole Information Paradox' Contact : Andrea Puhm Dates 
Gravity and Strings Conference Organized by Luca Ciambelli
Speakers :
Carlo Angelantonj
Contact : ciambelli.lucca@gmail.com

Andrea Puhm sur France Culture le 10 septembre 2019 Andrea Puhm, chargée de recherche au Centre de Physique Théorique a été invitée à parler de supergravité dans l'émission " La méthode scientifique" sur France ulture le 10 septembre 2019. En savoir plus ici. 
Andrea Puhm, lauréate de l’ERC Starting Grant 2019 Chargée de recherche du CNRS au Centre de physique théorique de l’École polytechnique, Andrea Puhm a été distinguée par une bourse ERC Starting Grant qui va lui permettre de lancer un groupe de recherche sur la thématique «Codage d'information en gravité quantique et le paradoxe d'information des trous noirs». En savoir plus ici 
Séminaire des cordes le lundi 22 novembre 2021 à 11h00 au CPHT, Salle de conférence Louis Michel ChernSimons supergravity and black holes with unbroken supersymmetries We study particular supersymmetric extension of EinsteinGaussBonnet AdS gravity in five dimensions. The theory admits black hole solutions with nontrivial 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 threedimensional BTZ geometries.
Conformal renormalization in AdS gravity We present evidence that the renormalization of EinsteinAdS 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 EinsteinAdS action is naturally endowed with the correct counterterms. 