Le serveur de séminaires SEMPARIS accueille toutes les annonces de séminaires de la région parisienne, dans tous les domaines de la physique et des mathématiques. Il vous permet aussi de recevoir par courrier électronique la sélection de votre choix. Enfin, il permet l'archivage des présentations au format PDF ou Powerpoint. [ Plus d'informations ]
Séminaires à venir  [30 suivants]  
[ vue agenda ] 
Lundi 19 Fevrier 2018, 14:30 à CPHT, Aile 0  SEMCPHT (Séminaire du CPHT)  hepth 



Abstract:  In this talk, I will explain our recent studies in which we developed ways to calculate relative entropy in CFT, and the applications of the results, in particular, to bulk physics (1705.01486) and scrambling (to appear soon). (basé sur 1705.01486 ) 
Mardi 20 Fevrier 2018, 11:00 à CPHT, Salle de conférences Louis Michel, bât. 6  IPNX (Séminaire commun de physique théorique des particules IPNCPHTX)  hepph 



Abstract:  The computation of twoloop 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 twoloop 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 twoloop fivegluon QCD amplitude. 
Mardi 20 Fevrier 2018, 11:30 à LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  After a short review on divergent series and Borel resummation I will discuss a geometric approach based on PicardLefschetz theory which can be used to characterize when the perturbative series gives the full answer and when the inclusion of nontrivial saddlesinstantons is mandatory. I will then consider the \lambda \phi^4 model in one and two dimensions and show that by resummation of the perturbative series it ispossible to extract some nonperturbative information, such as the nonperturbative level splitting in the quantum mechanical double well and the critical parameters at the phase transition in the quantum field theory case. 
Mercredi 21 Fevrier 2018, 11:00 à IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  We study the spectrum of local operators living on a defect in a generic conformal field theory, and their coupling to the local bulk operators. We establish the existence of universal accumulation points in the spectrum at large s, s being the charge of the operators under rotations in the space transverse to the defect. Our tools include a formula that inverts the bulk to defect OPE and is analytic in s, analogous to the CaronHuot formula for the fourpoint function. Some important assumptions are made in deriving this result: we comment on them. 
Jeudi 22 Fevrier 2018, 11:00 à IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  Causality places nontrivial constraints on QFT in Lorentzian signature, for example fixing the signs of certain terms in the low energy Lagrangian. In these pedagogical lectures, I will explore causality constraints on conformal field theory. First, I will show how causality is encoded in crossing symmetry and reflection positivity of Euclidean correlators, and derive constraints on the interactions of lowlying operators directly from the conformal bootstrap. Then, I will explain the connection between these causality constraints and the averaged null energy condition. Finally, I will use causality to show that the averaged null energy is positive in interacting quantum field theory in flat spacetime. Based on arXiv:1509.00014, arXiv:1601.07904, arXiv:1610.05308. 
Jeudi 22 Fevrier 2018, 11:00 à LPT, 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  The computation of twoloop amplitudes forms a current bottleneck to computing precision level cross sections for LHC phenomenology. In this talk I will discuss several new methods for analytic evaluation of twoloop 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 twoloop fivegluon QCD amplitude. 
Vendredi 23 Fevrier 2018, 14:30 à IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  hepth 



Abstract:  Two versions of the SYZ conjecture proposed by Kontsevich and Soibelman give a differentialgeometric and a nonArchimedean recipes to find the base of the SYZ fibration associated to a family of CalabiYau manifolds with maximal unipotent monodromy. In the first one this space is the GromovHausdorff limit of associated geodesic metric spaces, and in the second one it is a subset of the Berkovich analytification of the associated variety over the field of germs of meromorphic functions over a punctured disc. In this talk I will discuss a toy version of a comparison between the two pictures for maximal unipotent degenerations of complex curves with flat metrics with conical singularities, and speculate how the techniques used can be extended to higher dimensions. 
Lundi 26 Fevrier 2018, 14:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTSTA (Séminaire de Physique Statistique, CEA/Saclay)  condmat 



Abstract:  Hydrodynamic interaction at micrometer scale has noticeable similarity with Coulomb interaction. Both of them are long ranged and are of great importance in understanding of functions and structures of biological systems at cellular level. Here I will talk about a few examples of interesting phenomena occurring in a system consisting of extended objects strongly coupled through hydrodynamic or Coulomb interaction. Firstly, the dynamics of microobjects, far from equilibrium, in hydrodynamic medium such as ciliary propulsion using hydrodynamic synchronization and chiral molecule separation using shear flow will be discussed. In the latter half of this talk, I will discuss condensation of charged biopolymers, which is in fact surprising and puzzling phenomena in sharp contrast with the common sense that like charges always repel. For example, DNA is a highly, negatively charged biopolymer, but these likelycharged DNA usually form strongly condensed phases. DNA condensations are effectively driven by short stiff polyamines such as spermine and spermidine. A recent progress explaining the prevailing role of polyamines on the charged biopolymer condensation will be presented. 
Mardi 27 Fevrier 2018, 11:30 à LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  TBA 
Mercredi 28 Fevrier 2018, 11:00 à IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  Causality places nontrivial constraints on QFT in Lorentzian signature, for example fixing the signs of certain terms in the low energy Lagrangian. In these pedagogical lectures, I will explore causality constraints on conformal field theory. First, I will show how causality is encoded in crossing symmetry and reflection positivity of Euclidean correlators, and derive constraints on the interactions of lowlying operators directly from the conformal bootstrap. Then, I will explain the connection between these causality constraints and the averaged null energy condition. Finally, I will use causality to show that the averaged null energy is positive in interacting quantum field theory in flat spacetime. Based on arXiv:1509.00014, arXiv:1601.07904, arXiv:1610.05308. 
Mercredi 28 Fevrier 2018, 11:30 à
IPN,
Bâtiment 100, Salle A015 ( $ $ )  IPNTHEO (Séminaire du groupe de physique théorique de l'IPN Orsay)  nuclth 



Abstract:  In free space, the interaction between a proton and a neutron allows the formation of the deuteron, the only twonucleon bound state in nature. Although the force between two neutrons (or two protons) is also attractive, it is not strong enough to hold a bound state in the form of a dinucleon. However, this picture changes drastically when the twonucleon interaction takes place in nuclear matter. In this seminar the formation of dinucleons is discussed as well as its implications on the singleparticle spectrum, superfluidity and the resulting EoS for nuclear matter.  
Fichiers attachés: 
Lundi 5 Mars 2018, 10:45 à LPTMC, Jussieu, tower 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  I will consider a system of N onedimensional free fermions confined by a harmonic well. At zero temperature (T=0), this system is intimately connected to random matrices belonging to the Gaussian Unitary Ensemble. In particular, the density of fermions has, for large N, a finite support and it is given by the Wigner semicircular law. Besides, close to the edges of the support, the quantum fluctuations are described by the socalled AiryKernel (which plays an important role in random matrix theory). What happens at finite temperature T ? I will show that at finite but low temperature, the fluctuations close to the edge, are described by a generalization of the Airy kernel, which depends continuously on temperature. Remarkably, exactly the same kernel arises in the exact solution of the KardarParisiZhang (KPZ) equation in 1+1 dimensions at finite time. I will also discuss recent results for fermions in higher dimensions. 
Mardi 6 Mars 2018, 10:30 à
IHES,
Amphi. Léon Motchane ( Cours des Professeurs Permanents de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  The course will focus on rigorous results for the selfavoiding walk model on lattices, with a special emphasis on lowdimensional ones. The model is defined by choosing uniformly at random among random walk paths starting from the origin and without selfintersections. Despite its simple definition, the selfavoiding walk is difficult to comprehend in a mathematically rigorous fashion, and many of the most important problems illustrating standard challenges of critical phenomena remain unsolved. The model is combinatorial in nature but many questions about the stochastic properties of these random paths can be solved by combining nice combinatorial features with probabilistic techniques. In the course, we will describe some of the recent techniques developed in the area, including the use of discrete holomorphicity to understand the model on the hexagonal lattice. 
Mardi 6 Mars 2018, 11:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTGEN (Séminaire général du SPhT)  physics 


Mardi 6 Mars 2018, 14:00 à APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 


Mardi 6 Mars 2018, 16:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 


Mardi 6 Mars 2018, 17:15 à DPTPHYSENS, room Jean Jaurès (29 rue d'Ulm)  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  astroph 



Abstract:  For the first time, starting more than two years ago, the advanced LIGO and Virgo instruments have directly observed gravitational waves. The first signals seen were from the mergers of pairs of massive black holes, and more recently we have also observed the inspiral and merger of two neutron stars. I will talk about the history and current status of this field, the basic physics of our observations, and some of our hopes and expectations for the future. 
Mercredi 7 Mars 2018, 11:00 à IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  Causality places nontrivial constraints on QFT in Lorentzian signature, for example fixing the signs of certain terms in the low energy Lagrangian. In these pedagogical lectures, I will explore causality constraints on conformal field theory. First, I will show how causality is encoded in crossing symmetry and reflection positivity of Euclidean correlators, and derive constraints on the interactions of lowlying operators directly from the conformal bootstrap. Then, I will explain the connection between these causality constraints and the averaged null energy condition. Finally, I will use causality to show that the averaged null energy is positive in interacting quantum field theory in flat spacetime. Based on arXiv:1509.00014, arXiv:1601.07904, arXiv:1610.05308. 
Jeudi 8 Mars 2018, 14:00 à LPTMC, Jussieu, tower 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  This talk will focus on the question of the physical contents of the GibbsShannon entropy outside equilibrium. Article : GavrilovChetriteBechhoeffer : Direct measurement of weakly nonequilibrium system entropy is consistent with GibbsShannon form. PNAS 2017. 
Vendredi 9 Mars 2018, 10:00 à
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/196 )  COURS (Cours)  hepth 



Abstract:  It is known since the work of Emmy Noether that continuous global symmetries lead to local conserved currents. In gauge theories such as electromagnetism or gravity, the currents associated to gauge transformations vanish because gauge symmetries are not physical symmetries, but rather redundancies of description. However, if the manifold on which the gauge theory is defined has a boundary and the gauge parameter does not vanish on it, then the associated conserved charge can be nonzero. Such gauge transformations that do not vanish at infinity are known as asymptotic symmetries and they act nontrivially on the space of states. \par Asymptotic symmetries make a natural appearance in holography, the proposed equivalence between a theory of quantum gravity on a given manifold and a field theory living on its boundary. More precisely, they should correspond to global symmetries of the dual field theory. Despite the huge success of the AdS/CFT holographic correspondence, holography for most spacetimes of interest remains very poorly understood. One may then hope that the study of asymptotic symmetries, especially when there is an infinite number of them, can shed light on the nature of the dual field theory. \par In this course, we will study several examples of gravitational backgrounds for which the group of asymptotic symmetries is infinitedimensional, such as AdS$_3$, the near horizon of extreme black holes, and flat space. In the latter case, a parallel development relates asymptotic symmetries to the soft behaviour of scattering amplitudes, providing a new perspective on these wellknown results. The black holes will always be lurking in the background. \\ \\ 1. Introduction to the covariant phase space formalism and construction of the conserved charges. \\ 2. Asymptotic symmetries of AdS$_3$ gravity and generalization to extreme Kerr black holes. \\ 3. Asymptotic symmetries of flat space: supertranslations, superrotations and the memory effect. \\ 4. Symmetries of scattering in flat space and relation to soft theorems.  
Fichiers attachés: 
Lundi 12 Mars 2018, 10:45 à LPTMC, tower 1312 5th floor room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  This talk will show that bacterial suspensions, beyond their intrinsic, dominating importance in biology, are also excellent systems to explore and test theoretical results on active matter, I will present recent experimental results on dense bacterial suspensions obtained in the groups of Masaki Sano (University of Tokyo), Yilin Wu (Chinese University of Hong Kong), and Hepeng Zhang (Shanghai Jiaotong University). I will put them in context, situating them within our current knowledge of active matter, stressing differences and similarities. Particular attention will be paid to the modeling efforts already deployed or to be developed in order to understand the fascinating largescale phenomena observed by these 3 groups. 
Mardi 13 Mars 2018, 10:30 à
IHES,
Amphi. Léon Motchane ( Cours des Professeurs Permanents de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  The course will focus on rigorous results for the selfavoiding walk model on lattices, with a special emphasis on lowdimensional ones. The model is defined by choosing uniformly at random among random walk paths starting from the origin and without selfintersections. Despite its simple definition, the selfavoiding walk is difficult to comprehend in a mathematically rigorous fashion, and many of the most important problems illustrating standard challenges of critical phenomena remain unsolved. The model is combinatorial in nature but many questions about the stochastic properties of these random paths can be solved by combining nice combinatorial features with probabilistic techniques. In the course, we will describe some of the recent techniques developed in the area, including the use of discrete holomorphicity to understand the model on the hexagonal lattice. 
Mardi 13 Mars 2018, 11:30 à LPTHE, LPTHE library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  I will review the original motivation for the existence of fivedimensional superconformal fixed points from supersymmetry and branes and then discuss the recent construction of exact Type IIB supergravity solutions which are holographic duals to such theories. 
Mardi 13 Mars 2018, 14:00 à APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 


Jeudi 15 Mars 2018, 10:00 à
IHES,
Amphi. Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 


Jeudi 15 Mars 2018, 11:00 à LPTHE, bibliothèque  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  mathmath.MP 


Vendredi 16 Mars 2018, 10:00 à
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/196 )  COURS (Cours)  hepth 



Abstract:  It is known since the work of Emmy Noether that continuous global symmetries lead to local conserved currents. In gauge theories such as electromagnetism or gravity, the currents associated to gauge transformations vanish because gauge symmetries are not physical symmetries, but rather redundancies of description. However, if the manifold on which the gauge theory is defined has a boundary and the gauge parameter does not vanish on it, then the associated conserved charge can be nonzero. Such gauge transformations that do not vanish at infinity are known as asymptotic symmetries and they act nontrivially on the space of states. \par Asymptotic symmetries make a natural appearance in holography, the proposed equivalence between a theory of quantum gravity on a given manifold and a field theory living on its boundary. More precisely, they should correspond to global symmetries of the dual field theory. Despite the huge success of the AdS/CFT holographic correspondence, holography for most spacetimes of interest remains very poorly understood. One may then hope that the study of asymptotic symmetries, especially when there is an infinite number of them, can shed light on the nature of the dual field theory. \par In this course, we will study several examples of gravitational backgrounds for which the group of asymptotic symmetries is infinitedimensional, such as AdS$_3$, the near horizon of extreme black holes, and flat space. In the latter case, a parallel development relates asymptotic symmetries to the soft behaviour of scattering amplitudes, providing a new perspective on these wellknown results. The black holes will always be lurking in the background. \\ \\ 1. Introduction to the covariant phase space formalism and construction of the conserved charges. \\ 2. Asymptotic symmetries of AdS$_3$ gravity and generalization to extreme Kerr black holes. \\ 3. Asymptotic symmetries of flat space: supertranslations, superrotations and the memory effect. \\ 4. Symmetries of scattering in flat space and relation to soft theorems.  
Fichiers attachés: 
Vendredi 16 Mars 2018, 10:30 à
IHES,
Amphi. Léon Motchane ( Cours des Professeurs Permanents de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  The course will focus on rigorous results for the selfavoiding walk model on lattices, with a special emphasis on lowdimensional ones. The model is defined by choosing uniformly at random among random walk paths starting from the origin and without selfintersections. Despite its simple definition, the selfavoiding walk is difficult to comprehend in a mathematically rigorous fashion, and many of the most important problems illustrating standard challenges of critical phenomena remain unsolved. The model is combinatorial in nature but many questions about the stochastic properties of these random paths can be solved by combining nice combinatorial features with probabilistic techniques. In the course, we will describe some of the recent techniques developed in the area, including the use of discrete holomorphicity to understand the model on the hexagonal lattice. 
Lundi 19 Mars 2018, 10:45 à LPTMC, Jussieu, tower 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Lundi 19 Mars 2018, 14:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTSTA (Séminaire de Physique Statistique, CEA/Saclay)  condmat 



Abstract:  Controlling the selfassembly of supramolecular structures is vital for living cells, and a central challenge for engineering at the nano and microscales. Nevertheless, even particles without optimized shapes can robustly form welldefined morphologies. This is the case in numerous medical conditions where normally soluble proteins aggregate into fibers. Beyond the diversity of molecular mechanisms involved, we propose that fibers generically arise from the aggregation of irregular particles with shortrange interactions. Using minimal models of frustrated aggregating particles, we demonstrate robust fiber formation for a variety of particle shapes and aggregation conditions. Geometrical frustration plays a crucial role in this process, and accounts for the range of parameters in which fibers form as well as for their metastable, yet longlived character. 
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