The center for Theoretical Physics (CPHT) at Ecole Polytechnique gathers research scientists working in diverse domains of fundamental and applied Physics. The overall coherence is assured by the corpus of common, transposable, mathematical and numerical methods.
CPHT is a joint research unit of CNRS and Ecole Polytechnique, and has a partnership with the Collège de France. His director is Jean-René Chazottes, Senior Researcher at CNRS.
CPHT is on the campus of Ecole Polytechnique, buildings 5 and 6. The reception offices are located in building 6 , offices 06.1046 and 06.1045.
 

Postal Address :
CPHT 
Ecole Polytechnique 
91128 Palaiseau cedex 
France

Secretary phone number : 01 69 33 42 01 (from abroad: +33 169 334 201)

Write an email to someone at CPHT :  : firstname.lastname@polytechnique.edu

 

 

Marcello Turtulici soutiendra publiquement ses travaux de thèse le 10 décembre 2021  au CPHT, Salle de conférence Louis Michel.

Titre de la thèse : "Ab-initio investigation of non-stoichiometric transition metal oxides"

Composition du Jury

Rapporteurs : Ferdi Aryasetiawan, Jan Martin Tomczak
Presidente : Lucia Reining
Examinateurs : Dipankar Das Sarma, Alaska Subedi
Directrice de these : Silke Biermann

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Phd student

Research group : Mathematical physics

Thesis: "Renormalization of quantum field theories that break translation invariance."
Advisor: Christoph Kopper

Research interests

flow equations, renormalization group, quantum field theory, half-space, lattice, film geometry, Casimir effect

Quantum field theories that break translation invariance appear in many physical context. The translation invariance can be broken by the regularization scheme used such as the lattice regularization [1], by the geometry of the space-time (a Riemanian manifold for example) [2], or by the presence of a boundary. When the loss of this symmetry is induced by the properties of the space-time, the renormalization of the QFT is affected. The less symmetric the theory is, the more counter-terms are needed to make it finite. The aim of this thesis is to study first the perturbative renormalization of the massive scalar field theory with a quartic interaction regularized by a lattice, using the method of the flow equations and prove that the Euclidean symmetries are restored in the continuum limit. We would like also to investigate the perturbative renormalizability of boundary field theories. The massive scalar field theory in a half-space [3] is the simplest model of such theories. We compute first all the possible propagators that correspond to all possible boundary conditions and prove the renormalizability of this theory for the Robin boundary condition.

[1] M. Borji, Ch. Kopper, Perturbative renormalization of the lattice regularized phi 44 with flow equations, Journal of Mathematical Physics. 2020;31(11):112304.
[2] Ch. Kopper, V. F. Müller, Renormalization proof for massive phi44 theory on Riemannian manifolds, Communications in Mathemathical Physics 2007; 275(2): 331-372.
[3] H.W. Diehl, in: Phase Transitions and Critical Phenomena, Vol. 10. Eds. C. Domb and J.L. Lebowitz (Academic Press, London, 1986) p. 75

 

Address CPHT, Ecole Polytechnique, 91128 Palaiseau cedex, France
Phone number 33 (0)1 69 33 42 46
Contact firstname.lastname@polytechnique.edu
Office Building 412, office 412.1026

 

English

 

The 2nd CPHT Young Researchers Seminar will be held on December 9, 2021 at 3:00 p.m. in the Louis Michel Conference Room with three presentations:

Yorgo Pano : Celestial holography in a nutshell

Duifje van Egmond : A novel background field approach to the confinement-deconfinement transition

Benjamin Bacq-Labreuil : Into the physics of real copper oxide materials

The seminar will be followed by a high tea.

English

 

Xiang ZHAO soutiendra publiquement ses travaux de thèse le jeudi 25 novembre 2021 à 10h00 au CPHT, Salle de conférence Louis Michel.

Titre de la thèse : "Aspects of Conformal Field Theories and Quantum Fields in AdS"
Directeur de thèse : Balt Van Rees

Participer à la réunion Zoom pour la soutenance de thèse :
https://us06web.zoom.us/j/87068486326?pwd=a0JMRkZBdEpkYzVDR0h4N2piQ1hNUT09
Meeting ID: 870 6848 6326
Passcode: 245657

Composition du Jury

(1) Christopher BEEM, Associate Professor, Oxford University (Rapporteur)
(2) Nikolay BOBEV, Associate Professor, KU Leuven (Rapporteur)
(3)Costas BACHAS, Directeur de Recherche, ENS (Examinateur)
(4) Christoph KOPPER, Professeur, Ecole Polytechnique (CPHT) (Examinateur)
(5) Eric PERLMUTTER, Assistant Professor, Saclay (IPHT) (Examinateur)
(6) Balt VAN REES, Professeur, Ecole Polytechnique (CPHT) (Directeur de thèse)

Abstract

"This thesis studies the structure and the space of conformal field theories (CFTs), and more generally various properties of conformal correlation functions. It extends into multiple directions, both perturbative and non-perturbative, local and non-local, with and without supersymmetry.
The first aspect concerns the conformal correlation functions in d-dimensional spacetime and their relation to flat-space S-matrices in (d+1)-dimensional spacetime. The connection is built up by considering a quantum field theory (QFT) in a fixed (d+1)-dimensional Anti-de Sitter (AdS) background and sending the radius of the AdS curvature to infinity. That is, the central object to study is the flat-space limit of QFT in AdS. The analysis starts from taking the flat-space limit of the building blocks of Witten diagrams, namely the bulk-boundary and bulk-bulk propagators. This analysis leads to conjectural generic prescriptions to extracting flat-space physics from conformal correlators. Interestingly, the intuitional picture that a Witten diagram simply reduces to the corresponding Feynman diagram does not always hold, and the origin of this discrepancy lies in the bulk-bulk propagators: they could have two different flat-space limits. One of the limits always exists and reduces to Feynman propagator, while the other, when present, can diverge in the flat-space limit. This observation is tested by explicit examples, including fourpoint scalar contact, exchange and triangle Witten diagrams and the conjectures are expected to work whenever the scattering energy is large enough.
The second aspect studies the classification problem of conformal defects. The goal is to partially answer the question: given a bulk CFT and consistency conditions such as crossing symmetry and unitarity, what are the allowed conformal defects with a non-trivial coupling to the bulk? Analytic bootstrap techniques are applied to study a simplified version of this problem where in the bulk only a single free scalar field is considered. Analysis of various three-point functions among bulk and defect fields leads to the conclusion that almost all the n-point correlation functions of defect fields are completely fixed up to a potentially unfixed one-point function. This analysis also leads to an intermediate result in which it is proven that the n-point correlation functions of a conformal theory with a generalised free spectrum must be those of the generalised free field theory."

The third aspect studies the interplay between analyticity in spin in CFTs and supersymmetry. Operator spectrum in a general unitary CFT is expected to be captured by a function analytic for spin J>1, and the operators are organised into various Regge trajectories. The presence of supersymmetry in general extends the region of analyticity in spin. The 6d N=(2,0) superconformal field theories (SCFTs) is considered as a concrete example, in which analyticity in spin is expected to hold down to J>−3. Detailed analysis of the four-point function of the the stress tensor supermultiplet uncovers an unexpected interplay between unprotected and protected multiplets: the stress tensor multiplet can be found on a long (unprotected) Regge trajectory when analytically continued to spin J=−2. In this study a general iterative bootstrap program is also established, which applies to all SCFTs that have a chiral algebra subsector.

 

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The students conference is organized this year on Friday, November 26, Becquerel amphitheatre.

speakers and titles

9h - 10h30

Sabine Harribey (A quick review of melonic CFTs - visio)
Jean-Gabriel Thiriet (Non-modal hydrodynamic stability analysis of ablation flows relative to inertial confinement fusion)
Matthieu Vilatte (Geroch method from holography fluid/gravity)
Ephraim  Bernhardt (Topology and disorder)
Yorgo Pano (Celestial holography)
Frederick del Pozo (Quantum field theory for topological superconductors)
David Rivera Betancour (Aspects of fluids and flat holography)

11h - 12h30

Filippo Sottovia (Can hydrodynamics correctly describe instabilities in superfluids? A holographic approach)
Gabriele Casagrande (The Swampland program and SUGRA inflationary models)
Erik Linner (Electronic correlations in incommensurate materials)
Long Zou (Propagation of ultra-fast laser pulse and filamentation in the air)
Benjamin Bacq-Labreuil (Exploring the physics of strongly correlated copper oxyde systems)
James Boust (Magnetism in correlated f-electron intermetallics)
Mohamed Rekhis (Toroidal alfven eigenmodes destabilisation by energetic particles in tokamaks)

14h - 15h30

Julian Legendre (Topological properties of the kagome lattice and light-matter systems)
Majdouline Borji (Perturbative renormalization of the semi-infinite phi_4^4 theory with flow equations)
Adrien Loty (Constraints on effective theories of quantum gravity)
Renaud Garioud (Perturbation theory for symmetry-broken systems: application to the Néel phase transition)
Marcos Gonzalez (Jet quenching in heavy ion collisions)
Zhaoxuan Zhu (Two-dimensional cold atoms in a quasicrystal lattice)
Jan Schneider (Out-of-equilibrium dynamics in long-range interacting many-body physics)

16h -16h50

Nahuel Barrios (Perturbative study of long-distance non-abelian gauge theories - visio)
Balthazar de Vaulchier (Wavefunction of the universe)
William Focillon (Mechanical properties of the nucleon in the scalar diquark model.)
Pauline Besserve (Unraveling strongly-correlated materials’ properties with noisy quantum computers)

Tea Time

English

!! Changement de lieu : La soutenance aura finalement lieu dans la salle de conférence du Centre de Mathématiques Laurent Schwartz 

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."

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An international collaboration involving researchers from the CPHT has revealed a new technique for generating short pulses of visible light. By injecting an infrared laser pulse into a hollow fiber, researchers from the Institut National de la Recherche Scientifique (Canada) have been able to create very short pulses of visible light at the exit, without needing to compress them. This technique takes advantage of the multimode nature of the fiber to promote the transfer of infrared energy to the visible region of the spectrum.

Arnaud Couairon, CNRS research director at CPHT and Jeffrey Brown (post-doctoral fellow at CPHT from 2016 to 2019) participated in developing the theoretical model of this phenomenon with their collaborators from the University of Louisiana (USA) and Heriot-Watt University (Scotland). Their work has been published in the prestigious journal Nature Photonics.

English

 

Post Doctoral Fellow

Research group: Condensed Matter

Research interests

My main research interest is in the strongly correlated electron systems. They form one of the most active fields in condensed matter physics due to the number of interesting phenomena observed experimentally and predicted theoretically in them. In my work I have studied both simplified models and real materials, by mainly using two methods, the Dynamical Mean-Field Theory (DMFT) and the Slave Spins Mean-Field (SSMF). During my PhD I focused on the class of Hund metals (multi-orbital systems where the Hund's coupling plays a predominant role), exploring their rich phase diagram. Moreover, I have worked on transport calculations for various models and realistic simulations. Currently I am interested in exploring non-local effects on different strongly correlated systems and in particular on the Hund metal physics.

Link to publication list: https://scholar.google.fr/citations?user=jjLzZrEAAAAJ&hl=el

PhD Thesis:

Title: "Charge instabilities, Mott transition and transport in Hund metals" Advisor: Prof. Luca de' Medici
University: ESPCI Paris, PSL
Defense date: 13/07/2021
https://theses.fr/2021UPSLS056

 

Email firstname.lastname@polytechnique.edu
Phone number +33(0) 1 69 33 42 90
Address CPHT, Ecole Polytechnique, 91128 Palaiseau cedex, France
Office 'Aile 0', office 1011

 

English

 

The 1st CPHT Young Researchers Seminar will be held on October 27, 2021 at 3:00 p.m. in the Louis Michel Conference Room with three presentations given by the following PhD students:

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

The seminar will be followed by a high tea.

English

 

Thibaut Coudarchet will defend his Ph.D on Thursday 30th of September at 2pm. The defense will take place in "Amphi Lagarrigue".

Do not hesitate to join, simply do no forget to wear a mask.

There is also a zoom link to attend the defense online that I give you here:
30 sept. 2021 02:00 PM Paris
Zoom link:
https://us02web.zoom.us/j/81787410532

ID: 817 8741 0532

The title of the thesis is "String theory: Supersymmetry breaking, moduli stabilization and cosmological considerations".

Jury Members

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

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