Prochains séminaires

Calendrier des séminaires du groupe des Cordes

Séminaires du Département de Physique

Le serveur des séminaires parisiens

Les séminaires au CPHT :

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 :

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

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


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 Brown
Université de Louisiane, Baton Rouge et
Centre de Physique Théorique, Ecole polytechnique  

Modeling ultrashort laser pulses in gases


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


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 QCD
We 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



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


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.