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Les anciens séminaires du CPHT

Séminaire Plasma du Centre de Physique Théorique de l’Ecole Polytechnique
Vendredi 25 janvier 2013, 10h30
Salle de conférence du CPHT
Prof. Karl Krushelnick Center for Ultrafast Optical Science (CUOS) and Dept. of Nuclear Engineering, University of Michigan - actuellement LOA / ENSTA
"High intensity laser plasma interaction experiments at the Center for Ultrafast Optical Science"
Recent results from experiments conducted at the Center for Ultrafast Optical Science (CUOS) at the University of Michigan will be described. These include a) wakefield acceleration and the generation of very collimated high energy positron beams, b) ion and proton acceleration in the radiation pressure acceleration regime, as well as c) measurements of the scaling of high order harmonic generation at ultra-high intensities for efficient attosecond pulse generation

Vendredi 1er Juin 2012 à 11H00
Salle de conférence du CPHT
Jeremy R. Gulley (Dept. of Biology and Physics , Kennesaw State University)
"Ultrashort pulse propagation and multi-chromatic ionization in dielectrics"

Abstract : The ubiquitous use of femtosecond lasers during the last 15 years has necessitated a detailed understanding of pulse propagation coupled with ultrafast laser-material interactions. Current ultrashort pulse propagation models describe the evolution of fields with broad spectra while models of ionization and laser-plasma interactions typically assume monochromatic laser fields. In this seminar I address the contradiction of combining multi-chromatic propagation models with monochromatic laser-material descriptions. Recently published experimental and simulation results are presented that show how this contradiction leads to order-of-magnitude errors in calculating the ionization yield. Further simulation results suggest that multi-chromatic effects will alter the shape and severity of laser-induced modifications to dielectric solids. I will end by discussing the possible impacts of multi-chromatic effects for ultrashort pulse filamentation and material processing.

— -

Vendredi 13 Avril 2012 à 11H00
Salle de conférence du Centre de Mathématique CMLS (meme Batiment que le CPHT)
*Experiences d’interaction sur la LIL en 2011*
Pascal Loiseau et Christophe Rousseaux
(CEA-DIF)

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Seminar at the interface between condensed matter and quantum optics, Salle de Conference of CPHT :

Jeudi 22 Décembre à 14h00, Salle de Conférence du CPHT

Dr Simone De Liberato (Universite Paris Diderot, Paris VII)
Quantum Vacuum Phenomena and Functional Quantum Biology

After a brief introduction on my previous works, I will present you my current research in two different fields : quantum vacuum phenomena and functional quantum biology. In the first I will show some recent results on mesoscopic vacuum forces, analogous of the usual Casimir force, that can be found in ultrastrongly coupled light-matter systems. In the second I will highlight the importance of quantum mechanics in living organisms, in particular showing how photosynthetic bacteria exploit quantum coherence to increase their efficiency. I will conclude discussing how the lessons learned from living organisms could pave the way to a new generation of optoelectronic and photovoltaic devices.

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Série Séminaires Plasma du Centre de Physique Théorique
Date Lundi 19 Septembre 2011 à 11H00
Lieu Salle de conférence du CPHT, Ecole Polytechnique
Orateur P. Prem Kiran (Advanced Centre of Research in High Energy Materials (ACRHEM) University of Hyderabad, Hyderabad 500046, India)
Titre Laser-matter interaction at ns and fs time scales
Résumé Our attempt to understand the basic phenomenon of energy deposition and dissipation resulting from the ns laser induced breakdown of materials will be discussed, focusing on the characterization of (a) laser induced shockwave and cavitation bubble dynamics with ns temporal resolution and (b) spectral emissions from laser induced breakdown spectroscopy (LIBS) to identify the hazardous materials. Our efforts in understanding the recently observed phenomenon of fs pulse filamentation under tight focusing conditions and its effect on the evolution of supercontinuum from air and water will be presented.
Série Séminaires Plasma du Centre de Physique Théorique
Date Lundi 19 Septembre 2011 à 14H00
Lieu Salle de conférence du CPHT, Ecole Polytechnique
Orateur Dr. Devki Nandan Gupta (Department of Physics and Astrophysics Norh Campus, University of Delhi, Delhi-110007, India)
Titre Nonlinear interaction of a laser with a Density Modulated Plasma
Résumé In this talk, I will present most of my work carried out on electron acceleration. Some extended work on beat-wave acceleration and Laser WakeField Acceleration will be presented.
ATTENTION Séminaire ANNULE
Série Séminaires Plasma du Centre de Physique Théorique
Date Vendredi 23 septembre 2011 à 11H00
Lieu Salle de conférence du CPHT, Ecole Polytechnique
Orateur Dr. Bedros B. Afeyan (Polymath Research, Pleasanton, California)
Titre Optimal control of laser plasma instabilities using Spike Trains of Uneven Duration and Delay (STUD pulses) for ICF and IFE
Série Seminaire commun IPN-X(Particules)
Date Lundi 18 Octobre 2010 à 14h00
Attention jour et heure inhabituels
Lieu Salle de conférence du CPHT, Ecole Polytechnique
Orateur Cédric LORCÉ (Johannes Gutenberg—Universitat, Mainz)
Titre Large Parton distributions
Résumé I propose a tour in the realm of parton distributions from the phenomenological point of view. Part of the presentation will be devoted to the connection between the different parton distributions and to their physical interpretation. Some manifestations of orbital angular momentum will be discussed as well as the problem of determining its contribution to the total angular momentum of the proton. I will also present a general expression for the three-quark amplitude in constituent quark models on the light cone. This allows one to estimate within a single formalism all the parton distributions and to look for possible links between different subsets of parton distributions.
Série Seminaire commun IPN-X(Particules et Cordes)
Date Mardi 19 Octobre 2010 à 11h00
Attention jour inhabituel
Lieu Salle de conférence du CPHT, Ecole Polytechnique
Orateur Mariano Quiros (IFAE - Barcelona)
Titre A Radion-induced supercooled EWPT
Résumé In the Randall-Sundrum model there are two phases at high temperature : the AdS-Schwarzschild (deconfining) phase and the RS (confining) phase. In the presence of a stabilizing field there is a radion phase transition between the deconfining and the confining phases. If the Higgs is localized towards the IR brane the latter triggers a supercooled electroweak phase transition. We will study its properties.
Série Seminaire commun IPN-X(Particules)
Date Jeudi 28 Octobre 2010 à 11h00
Lieu Salle de conférence du CPHT, Ecole Polytechnique
Orateur Vincent Pangon (GSI—Darmstadt)
Titre Structure of the broken phase of the sine-Gordon model using functional renormalization
Résumé We study the sine-Gordon model using functional Renormalization Group (fRG) at Local Potential Approximation (LPA) using different RG schemes. In d = 2, using Wegner-Houghton RG we demonstrate that the location of the phase boundary is entirely driven by the relative position to the Coleman fixed point even for strongly coupled bare theory. We show the existence of a set of IR fixed points in the broken phase that are reached independently of the bare coupling. The bad convergence of the Fourier series in the broken phase is discussed and we demonstrate that these fixed-points can be found only using a global resolution of the effective potential. We then introduce the methodology for the use of Average action method where the regulator breaks periodicity and show that it provides the same conclusions for various regulators. The behavior of the model is then discussed in d = 2 and the absence of the previous fixed points is interpreted.
Série Séminaire Plasma LULI/CPHT
Date Vendredi 24 Septembre 2010 à 10H00
Lieu Salle de conférence du LULI, Ecole Polytechnique
Orateur Bedros Afeyan, Polymath Research Inc., Pleasanton, CA, 94566)
Titre “Challenges in Nonlinear Optics of Plasmas in the NIC, ICF, IFE and HEDLP**”
Résumé “A number of concrete challenges exist when high intensity lasers illuminate plasmas in ICF and IFE conditions. Some that afflict the NIC at present will be highlighted. For direct and indirect drive, shock and fast ignition, the challenges are different but equally daunting. A new technique invented at PRI promises to be adaptable to these different circumstances. The new idea is called STUD pulses, for Spike Trains of Uneven Duration and Delay. It can reduce instability levels by orders of magnitude and take advantage of three different mechanisms to curtail their growth and self-organization. One is the appeal to damping of the driven waves in between the spikes. A second is illuminating the laser hot spots only partially by modulating the laser pulses on time scales short compared to the time it takes for the scattered light wave to traverse the pump laser hot spot’s full length, and the third is to scramble the hot spot distributions in space in successive spikes and thus not allow sustained growth of the driven waves in the plasma by the same repeated hot spot structure, as would be the case, for instance for RPP (Random Phase Plate) or SSD (Smoothing by Spectral Dispersion) illumination scenarios. The full 4D scrambling of the illumination intensity maxima in space-time allows the breakthrough not present with weak and slow temporal modulation schemes. Also, and most significantly, interlacing the laser patterns of overlapping or crossing beams (with off segments in them which allow the interlacing) affords real control over their interactions which are dangerous and remain uncontrolled to date.

Theory and comprehensive simulation results will be shown to substantiate these ideas. In particular, STUD pulses will be compared to RPP cases in the weak and strong damping regimes for both f/8 and f/20 optics. Additionally, STUD pulse performance will be compared to Pseudo-STUD pulses. In the latter, the laser is modulated on the few fastest-instability growth-time, time scale, but the hot spot patterns are not scrambled in time (as would be the case for STUD pulses). They are kept fixed, instead. Various spike durations and gains of the instability in a single hot spot at the average intensity, G_SBS, will be shown. The totality of these cases allows us to gauge the relative importance or merits of the three physical mechanisms at play in reducing the growth and eliminating long range order in nonlinear optical processes in plasmas with STUD pulses.

The theory relies on the geometry of Gaussian Random Fields and various statistical estimates including techniques in extreme value theory. The essential ingredient in this work is to design pulse trains whose hot spot recurrence probability is low enough that most driven waves will be damped before hot spot recurrence occurs in large numbers. For fields close to being Gaussian, this is easily achieved. In this sense, STUD pulses are optimal for long nanosecond illuminations, just as long as the long pulses are broken up to small sections which last for a few psecs each with roughly equal off times in between. Laser pulse shaping technology which already exists to change the front end of lasers to construct STUD pules will also be discussed. It will be argued that this new methodology should be tested as soon as possible on LULI for eventual implementation on LMJ and the NIF in Blue (third harmonic of glass) or Green (second harmonic of glass) laser illumination conditions for a better chance at ignition than is afforded by current techniques.

** Work supported by a DOE NNSA-OFES Joint HEDLP program Grant and a DOE OFES SBIR Phase I Grant. ”

Série Séminaire de physique des plasmas
Date Lundi 28 Juin 2010 à 11H
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Wojciech Rozmus (Department of Physics, University of Alberta)
Titre “Channeling of relativistic laser pulses and particle acceleration”
Série Séminaire de physique mathématique
Date Jeudi 6 mai 2010 à 15h30
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Daniele Oriti (Albert Einstein Institute))
Titre The microscopic dynamics of quantum space as a group field theory
Résumé We give an introduction to the group field theory approach to quantum gravity. This is a generalization of matrix models for 2d gravity to higher dimensions, and a framework that brings together elements from other approaches like loop quantum gravity, non-commutative geometry and simplicial quantum gravity. We also report on some recent results obtained in this context, concerning both the mathematical definition and properties of group field theory models and possible avenues for extracting physical predictions from them.
Série Séminaire de physique des plasmas
Date Mercredi 31 Mars 2010 à 14H15
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Ed Williams (Lawrence Livermore National Laboratory (LLNL))
Titre Laser plasma Interactions in the NIF Ignition Energetics Campaign
Série Séminaire de physique mathématique
Date Vendredi 19 mars 2010 à 15h30
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Walter D. van Suijlekom (Radboud University Nijmegen and IHES)
Titre Renormalization Hopf algebras for gauge theories and BRST symmetries
Résumé The structure of the Connes—Kreimer renormalization Hopf algebra is studied for Yang-Mills gauge theories, with particular emphasis on the BRST-formalism. A coaction of the renormalization Hopf algebra is defined on the coupling constants and the fields. In this context, BRST-invariance of the action implies the existence of certain Hopf ideals in the renormalization Hopf algebra, encoding the (physical) Slavnov-Taylor identities for the coupling constants.
Série Séminaire de physique mathématique
Date Vendredi 12 février 2010 à 15h30
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Paul-Andre Mellies (Jussieu)
Titre String diagrams, a topological account of proofs and programs
Résumé In this introductory talk, I will explain some of the functorial ideas which recently appeared in the field of logic and programming language semantics. More specifically, I will explain how to see game semantics as a variant of functorial knot theory, where the ribbon category of knots is replaced by a monoidal category of formulas and proofs between them. By the wizardry of string diagrams in 3-categories, this category may be seen alternatively as a category of games and interactive strategies between them. Interestingly, this game construction defines the free symmetric monoidal category equipped with a logical duality. From this follows the idea of classifying the various notions of duality in monoidal categories, the usual duality of ribbon categories being one of them. For the fun of it, I will also describe how to compute the free monoid in that category of games, using a left Kan extension, and relate this construction to the ability to define recursive calls in programming languages. Finally, I will draw a beautiful connection between logic and algebra, first noticed by Ross Street, and explain in what sense this category of games may be seen as a lax notion of Frobenius algebra. Amusingly, this observation leads to a lax version of two-dimensional cobordism, where particles are replaced by game boards.
Série Séminaire commun : Séminaire groupes quantiques et géométrie de Poisson et Séminaire de Physique Mathématiques (CPHT) Organisé par P. Cartier, D. Hernandez, Y. Kosmann-Schwarzbach et A. Tanasa
Date Mardi 16 février 2010
Lieu Salle de conférence du Centre de Mathématiques Laurent Schwartz, Bat. 6, Ecole Polytechnique
14h00 Alexander POLISHCHUCK (University of Oregon et IHES) "A-infinity structures and Yang-Baxter equations"
15h30 Robin ZEGERS (Orsay) "Règle de Dorey et q-caractères"
Série Séminaire Plasma du Centre de Physique Théorique
Date Vendredi 22 Janvier 2010 à 11H00
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Cédric Thaury
Titre "Effets multi-dimensionnels dans un plasma en expansion : influence des collisions Coulombiennes et de l’instabilité de Weibel"
Série Séminaire de physique mathématique
Date Vendredi 22 Janvier 2010 à 15h30
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Fabien Vignes-Tourneret (Lyon)
Titre Représentation paramétrique d’une théorie des champs non commutative
Résumé Depuis environ dix ans, la théorie des champs sur espaces non commutatifs jouit d’un regain d’intérêt. Le premier modèle renormalisable de champ scalaire sur espace de Moyal a été obtenu en 2004 par H. Grosse et R. Wulkenhaar. Il a permis de mettre en avant la nécessité d’adapter la propagation à l’espace non commutatif sous-jacent. Après quelques rappels concernant la renormalisation des modèles sur espaces non commutatifs, nous présenterons la représentation paramétrique du modèle de Grosse et Wulkenhaar ainsi que ses liens avec la combinatoire.
Série Séminaire Plasma du Centre de Physique Théorique
Date Mardi 15 Décembre 2009 à 11H00
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Prof. Masakatsu Murakami (ILE Osaka, Japon)
Titre "Applications of ion acceleration physics - from advanced laser fusion to quasimonoenergetic ion generation by Coulomb explosions"
Série Séminaire de physique mathématique
Date Vendredi 4 Décembre 2009 à 15h30
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Alan Sokal (New York University and University College London)
Titre Some wonderful conjectures (but almost no theorems) at the boundary between analysis, combinatorics and probability
Série Séminaire de physique des plasmas
Date Vendredi 20 Novembre 2009 à 11H00
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Antonio Lotti (Universita dell Insubria, Como, Italy et Centre de Physique Théorique de l’Ecole Polytechnique)
Titre Energy density flux of space-time coupled wavepackets : Application to the characterization of ultrashort laser pulse filaments
Série Séminaire de physique des plasmas
Date Mardi 24 Novembre 2009 à 11H
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Nikolay Andreev (Joint Institute for High Temperatures of RAS, Russian Academy of Sciences, Moscow)
Titre Laser wakefield acceleration of supershort electron bunches in guiding structures
Abstract High gradient acceleration of electrons by plasma waves generated in plasma channels by short intense laser pulses is analyzed. The influence of the loading effect and initial emittance on the quality of accelerated electron bunches is studied for the proposed scheme of the bunch injection in front of the laser pulse, which opens an opportunity for monoenergetic acceleration of ultra-short electron bunches of sub-micron sizes to high energies.
N E Andreev* , S V Kuznetsov* , B Cros** , V E Fortov*, G Maynard** and P Mora***
* Joint Institute for High Temperatures of RAS, Russian Academy of Sciences, Moscow 125412, Russia
** Laboratoire Physique Gaz et Plasmas CNRS - Université Paris-Sud 11, F-91405 Orsay Cedex, France
***Centre de Physique Theorique, CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex, France
Série Séminaire de physique mathématique
Date 13 novembre, 15h30
Lieu Salle de conférence du CPHT, Bat. 6, Ecole Polytechnique
Orateur Matteo Smerlak (CPT Marseille & LPT Orsay)
Titre On the scaling behavior of 3d group field theory
Résumé Spinfoam models quantize a discretization of gravity with only finitely many degrees of freedom. From the perspective of quantum field theory, this drastic truncation of dynamics is analogous to the restriction of the path integral to a single Feynman diagram, and can only be justified by the renormalization group. Group field theory, a standard (albeit non-local) field theory whose Feynman amplitudes are spinfoam amplitudes, is a candidate framework to investigate such a renormalization group. In this talk, I will present results obtained in collaboration with J. Magnen, K. Noui and V. Rivasseau, concerning the scaling behavior of 3d GFT (0906.5477[hep-th]). In particular, I will give upper bounds on the degree of divergence of individual Feynman graphs, and show how they can be upgraded to the constructive level, where the whole perturbative series is resummed in a convergent way.
Série Séminaire de physique des plasmas
Date Mercredi 14 octobre 2009 à 14h15
Lieu Salle de conférence du CPHT
Orateur Dr Bedros Afeyan (Polymath Research Inc., Pleasanton, CA, 94566)
Titre STUD Pulses : a New Way to Control LPI in ICF and IFE**
Abstract The Control of LPI has been a pursuit of great interest over the last 4 decades. Since the inception of the field of ICF in the late sixties, coupling laser energy into a hohlraum or direct drive target has been plagued by undesirable resonant multi-wave coherent interactions which tend not to thermalize the energy, to scatter it out of the target, to preheat the fuel and otherwise make the energy deposition uncontrollable. We propose to remedy that by the design and implementation of a Spike Train of Uneven Duration and Delay (STUD) pulses instead of continuous multiple nanosecond pulses which reinforce coherent self organization of a plasma. We will compare and contrast this new technique with well established but manifestly limited methods of the past such as ISI, SSD and related concepts. We will emphasize the advantages of STUD pulses when it comes to the mutual interaction of multiple overlapped beams which is of crucial importance for both direct drive and hohlraum light entrance hole (LEH) physics. Examples of suppression and enhancement of LPI processes will be given where they may aid in the realization of shock ignition, for example. Two plasmon decay, Stimulated Raman and Brillouin scattering will all be treated.
** Work supported by a grant from the DOE NNSA/OFES Joint HEDLP Program, LANL and NRL.
Série Séminaire de physique des plasmas
Date Vendredi 9 octobre 2009 14h00
Lieu Salle de conférence du CPHT
Orateur Dr. Burak Yedierler (Middle East Technical University, Ankara, Turkey)
Titre Short pulse laser beam propagation in non-linear optical media : A variational Approach
Série Séminaire de Physique Mathématique
Date Vendredi 9 octobre 2009 15h30
Lieu Salle de conférence du CPHT
Orateur Francis Brown (Jussieu)
Titre Périodes des intégrales de Feynman
Abstract Je donnerai une présentation des intégrales de Feynman du point de vue paramétrique et ensuite je donnerai une explication combinatoire et géométrique pour l’apparence des multizetas dans les calculs des physiciens.
Série Séminaire commun IPN-X (particules et cordes)
Date Mardi 1er Septembre 2009 à 11h
Lieu Ecole Polytechnique, salle de conférence du CPHT)
Orateur Tzu-Chiang Yuan (Institute of Physics, Academia Sinica, Taipei)
Titre Double Action Dark Matter
Résumé Motivated by a two-bump (or 1-peak plus 1-hump) structure in the ATIC data, we perform a statistical analysis fitting the PAMELA and ATIC data to a dark matter model, in which the dark matter particle can undergo both annihilation and decay. Using a chi-square analysis we show that both data can be simultaneously fitted better with such a double-action dark matter particle. More recent data from the Fermi-LAT experiment will also be discussed.
Série Séminaire de Physique des Plasmas
Date Jeudi 9 Juillet 2009 à 11 h
Lieu Dans l’amphi Fresnel (salle 70, bat. "Levy" 402, en face du bat. 06 du CPHT)
Orateur M. Sherlock (Blackett Laboratory, Imperial College London)
Titre Universal scaling of the electron distribution function in relativistic laser-plasma interactions
Résumé We provide a formula for the distribution function of energetic electrons which stream in the forward direction when a relativistically-intense laser pulse irradiates a short-scale-length dense plasma at normal incidence. If the energy absorption fraction is known, the entire function can be characterized in terms of the laser intensity . A number of important characteristics can then be obtained, including the fast electron energy, current density and angle of ejection. We suggest an objective means for calculating the fast-electron energy which is approximately given by 2/3 of the vacuum oscillatory energy. This reduction in energy is shown to be consistent with the energy required to draw a return current.
Série Séminaire de physique des plasmas
Date Vendredi 3 Juillet 2009 à 11H00
Lieu salle conférence CPHT
Orateur Wojciech Rozmus (Department of Physics, University of Alberta, Edmonton, Alberta, Canada)
Titre Ultrashort laser pulse absorption in dense targets
Abstract A theory of ultrashort laser pulse absorption in dense targets is important for modeling of basic physics and applications of short laser pulse plasma interactions. Recent absorption measurements and large number of indirect observations point to complex scenarios of short laser pulse absorption where the laser prepulse, ionization physics, density profile modifications, collisional processes and collisionless mechanisms occur all within short pulse duration and contribute to the absorbed fraction of the incident laser energy. Also plasma conditions in the absorption region are determined by the energy transport into the dense plasma, which includes collisional and weakly collisional thermal transport.I will describe in this paper a model of ultrashort laser pulse absorption, which includes linear absorption and thermal transport into dense plasma. Plasma dielectric function in our model describes collisional and collisionless absorption mechanisms including the effect of electron-electron collisions. Thermal transport is modeled using nonlocal expressions that are valid in the weakly collisional regime. The inhibited and nonlocal thermal transport can contribute to the increase of the electron temperature in the skin layer. Theoretical predictions will be compared with the results of Vlasov-Fokker-Planck simulations for laser intensities below 1017 W/cm2. Also numerical simulations will illustrate transition into relativistic regime of laser intensities.
Série Séminaire de Physique Mathématique
Date vendredi 10 avril 15h30
Lieu salle conférence CPHT
Orateur Stefan Hollands (Cardiff)
Titre Perturbation theory in terms of vertex operator algebras
Abstract I outline an approach to quantum field theory wherein the operator product expansion (OPE) is elevated to the status of a fundamental property. It is argued that the expansion coefficients ought to satisfy certain "associativity constraints". These constraints can be presented using the language of vertex algebras. Perturbations of a field theory are then related to deformations of this vertex algebra. I derive rules for concretely calculating the perturbations in standard QFT’s such as \lambda \phi^4.
Série Séminaire de physique des plasmas
Date Mardi 31 mars, 15h00
Lieu salle conférence CPHT
Orateur Serguei Kalmykov (Institute for Fusion Studies, The University of Texas at Austin)
Titre Interaction of short intense laser pulses with rarefied plasmas : Relativistic nonlinear optics and electron acceleration
Série "Rencontre de Physique des Particules 2009"
Date 23 au 25 mars 2009
Lieu CPHT
Site http://www.cpht.polytechnique.fr/rpp09
Série Séminaire de Physique Mathématique du CPHT
Date vendredi 20 mars, 15h30
Lieu salle conférence CPHT
Orateur Manfred Salmhofer (Heidelberg)
Titre Onset of diffusion in the Anderson model
Résumé One formulation of the extended-states conjecture for quantum particles moving in the presence of weak disorder is that the motion is diffusive in the long-time limit. I review a proof that in three or more dimensions, diffusion sets in on time-scales t of order lambda^-2-delta, where delta>0, and lambda is the strength of the disorder. More precisely, the Wigner function associated to the quantum mechanical wave function converges weakly to a solution of the heat equation in a scaling limit, where lambda goes to 0 with t lambda^-2-delta kept fixed, and where space is rescaled appropriately. This is joint work with L. Erdoes and H.-T. Yau.
Série Séminaire de Physique Mathématique du CPHT
Date vendredi 13 mars, 15h30
Lieu salle conférence CPHT
Orateur Razvan Gurau (Perimeter Institute, Canada)
Titre Hunting bubbles in Group Field theory
Résumé Group field theory is a generalization of matrix models. In 3 dimmensions its graphs are dual to 3D simplicial complexes. As such they are charcterized by several topological numbers : number of vertices N, lines L, faces F and bubbles B. In this talk we give the algorhitm to identify the bubbles of a graph and the associated genus g_B of a bubble. We give a direct proof ot the 3D Euler relation N-L+F-B=-\sum_bubblesg_B.
Série Séminaire de Physique de Physique des Plasmas
Date vendredi 23 janvier, 14h00
Lieu salle conférence CPHT
Orateur C. Nguyen, CEA/DSM/IRFM, CEA-Cadarache, France)
Titre Interaction entre activité Magnéto-Hydrodynamique et particules rapides dans un tokamak, le cas du Beta Alfvén Eigenmode.
Résumé La fusion thermonucléaire par confinement magnétique nécessite d’obtenir un bon confinement des particules alpha produites par les réactions de fusion. Ces particules, de type supra-thermiques, sont malheureusement susceptibles d’exciter des instabilités collectives dites Magnéto-HydroDynamiques(MHD) au sein du plasma thermonucléaire, et ces instabilités sont capables en retour d’expulser les particules supra-thermiques. Il est donc indispensable pour assurer la réussite de la fusion par confinement magnétique de comprendre les mécanismes à l’origine de cette excitation et plus généralement l’interaction entre activité MHD et particules supra-thermiques, afin de la contrôler. Dans cette présentation, nous expliquerons le formalisme dit « MHD-cinétique » dans lequel cette analyse peut être effectuée, ainsi que les difficultés qu’elle contient. Nous nous intéresserons plus particulièrement à un type de mode, le Beta Alfvén Eigenmode (BAE), dont il a été observé expérimentalement qu’il pouvait être à l’origine d’importantes pertes de particules rapides dans un tokamak. Tout d’abord, nous présenterons une dérivation théorique des propriétés linéaires de ce mode (sa structure et sa fréquence linéaire, son seuil d’excitation linéaire) en distinguant clairement les phénomènes MHD et les phénomènes cinétiques entrant dans cette description, puis nous montrerons les résultats d’une comparaison de ces propriétés théoriques avec des expériences menées sur le tokamak Tore-Supra. Nous verrons cependant qu’une compréhension complète du BAE exige un passage à une description non-linéaire, et présenterons dans ce cadre une analyse préliminaire de la saturation du BAE.
Série Séminaire de pPhysique Mathématique du CPHT
Date vendredi, 30 janvier, 15h30
Lieu salle conférence CPHT
Orateur Z. Wang (Ecole Polytechnique et Vienne)
Titre Quantum field theory and graph polynomials
Résumé We investigate the relationship between the universal topological polynomials for graphs in mathematics and the parametric representation of Feynman amplitudes in quantum field theory. We show how the Symanzik polynomials of quantum field theory are particular multivariate versions of the Tutte polynomial, and how the new polynomials of noncommutative quantum field theory are particular versions of the Bollob\’as-Riordan polynomials.
Série Séminaire de physique mathématique du CPHT
Date vendredi, 5 decembre, 15h30
Lieu Bibliothèque du LPTP
Orateur Alain Sokal (New York University)
Titre The Multivariate Tutte Polynomial for Graphs and Matroids
Résumé The multivariate Tutte polynomial (known to physicists as the Potts-model partition function) can be defined on an arbitrary finite graph G, or more generally on an arbitrary matroid M, and encodes much important combinatorial information about the graph (indeed, in the matroid case it encodes the full structure of the matroid). It contains as a special case the familiar two-variable Tutte polynomial --- and therefore also its one-variable specializations such as the chromatic polynomial, the flow polynomial and the reliability polynomial --- but is considerably more flexible. I begin by giving an introduction to all these problems, stressing the advantages of working with the multivariate version. I then discuss some questions concerning the complex zeros of the multivariate Tutte polynomial, along with their physical interpretations in statistical mechanics (in connection with the Yang—Lee approach to phase transitions) and electrical circuit theory. I also discuss some questions concerning correlation inequalities. Along the way I mention numerous open problems.
Série Séminaire commun de physique mathématique CPHT-LPT (Orsay)
Attentionjour et lieu inabituels
Date Mercredi 12 novembre, 11h30
Lieu salle 114, LPT Orsay
Orateur Daniel Blaschke (ITP Vienne)
Titre Towards a renormalizable translation-invariant model for non-commutative gauge fields
Résumé I will start my talk with a brief review of the UV/IR mixing problem of non-commutative field theories and how to solve it for a scalar field by adding a non-local counter term $\phi(-p) a^2/p^2 \phi(p)$ to the action. Some one-loop results for this model are then going to be presented in order to motivate a candidate for a renormalizable non-commutative gauge model. A discussion of this latter model including some recent one-loop results will then constitute the second part of my talk.
Série Séminaire commun de physique mathématique CPHT-LPT (Orsay)
Date vendredi 14 novembre, 15h30
Lieu salle de conferences de CMLS, Ecole Polytechnique
Orateur K. Noui (LMPT Tours)
Titre Spin-Foam models of quantum gravity
Résumé Spin-Foam models have been developped to understand the problem of the dynamics in loop quantum gravity. They propose a combinatorial formulation of the path integral of gravity based on the theory of topological invariants of manifolds. Physically, spin-foam models offer a picture of "the dynamics of a quantum geometry". In this seminar, I will review the basis of spin-foam models. I will explain in what sense they are a generalizations of 2 dimensional matrix models. Then I will explain how they are related to quantum gravity in 3D and 4D.
 Date 13 et 14 novembre 2008 Série Atelier (Workshop) sur l’Interaction laser-plasma dans les regimes d’impulsion pico- et nanoseconde Résumé Instabilités paramétriques  Propagation des faisceaux laser et lissage dans le plasma  Ondes plasmas non linéaires  Effets cinétiques et leur modélisation  Transport non local dans des plasmas créés par laser programme provisoire http://www.cpht.polytechnique.fr/spip.php?article13
Série Seminaire commun de physique mathematique CPHT-LPT Orsay
Date vendredi 24 octobre, à 15h30
Lieu Salle de Conferences du CPHT , Ecole Polytechnique
Orateur Karim Noui (LMPT Tours)
Titre Loop Quantum Gravity : a status
Résumé Loop Quantum Gravity is a candidate for a quantum theory of general relativity. It is based on a canonical non-perturbative background independent quantization of Einstein-Hilbert theory. In this seminar, I would like to first review the basis of LQG and then to discuss its successes, problems and open issues.
Série Soutenance de thèse du CPHT
Date Jeudi 9 Octobre 2008 à 14h
Lieu Amphi Becquerel, Ecole Polytechnique
Orateur Lam DAO
Titre Etudes des atomes froids fortement corrélés dans les réseaux optiques
Résumé This thesis is concerned with the theoretical study of strongly correlated quantum states of ultra-cold fermionic atoms trapped in optical lattices. The trapping of these gases in optical lattices has opened a new field of research at the interface between atomic physics and condensed matter physics. The observation of the transition from a superfluid to a Mott insulator for bosonic atoms paved the way for the study of strongly correlated phases and quantum phase transitions in these systems. Very recently, the investigation of the Mott insulator state of fermionic atoms provides additional motivation to conduct such theoretical studies. This thesis can be divided broadly into two types of work.

On the one hand, motivated by the direct observation of single-particle excitations in condensed matter by angular resolved photoemission spectroscopy (ARPES), we propose a spectroscopic method which aims at observing the Fermi surface and the spectrum of one-particle excitations in ultra-cold atomic systems. Our method is based on stimulated Raman spectroscopy. We show that, using this method, both the Fermi surface and the key physical properties of quasi-particle excitations can be accessed in a momentum and energy-resolved manner, under realistic experimental conditions in the presence of a confining potential. Recently, a closely related measurement has been realized in D.S. Jin’s group at Boulder by using RF spectroscopy.

On the other hand, we have studied the ground state of the fermionic Hubbard model under different conditions (mass imbalance, population imbalance) by using analytical techniques and numerical simulations. We demonstrated the possibility to stabilize a polarized superfluid phase in the regime of strong correlations. We used for this purpose general energetic arguments, as well as analytical and numerical calculations based on static mean field theory and dynamical mean field theory.

Série Seminaire commun de physique mathematique CPHT-LPT Orsay
Date vendredi 10 octobre, à 15h30
Lieu Salle de Conferences du CPHT , Ecole Polytechnique
Orateur Alessandra Frabetti (Univ. Lyon I)
Titre Facteurs de renormalisation de la \phi^3 et algèbres de Hopf
Résumé Je présente une application de la méthode des algèbres de Hopf de la renormalisation pour calculer les facteurs de renormalisation de la théorie de champ \phi^3 en dimension 6.
Série Séminaire Physique des Plasmas
Date Vendredi 21 décembre 2007 à 11H00
Lieu Salle de conférence du CPHT
Orateur Thomas GRISMAYER (Centre de Physique Théorique, Ecole Polytechnique)
Titre Electron kinetic effects in plasma expansion and ion acceleration
série Séminaire de Physique des Plasmas
Date 25 Avril 2007
Lieu au CPHT, Salle de conférence
Orateur Nathanael SCHAEFFER LGIT (Laboratoire de Géophysique Interne et Tectonophysique)
Titre Instabilités, turbulence et dynamo dans une couche de fluide cisaillée en rotation
Résumé La motivation de ce travail est l’expérience au sodium liquide construite à Grenoble, elle-même motivée par la dynamo terrestre qui génère le champ magnétique à partir des mouvements de fer liquide dans le noyau.

Dans la limite d’une rotation d’ensemble rapide, je vais présenter les écoulements qui prennent place dans la sphère remplie de sodium qui représente le noyau terrestre, lorsqu’on impose un cisaillement.

Je montrerais ensuite que ces écoulements peuvent produire une dynamo, y compris dans la limite d’une diffusivité magnétique forte.