The SEMPARIS seminar webserver hosts annoucements of all seminars taking place in Paris area, in all topics of physics, mathematics and computer science. It allows registered users to receive a selection of announcements by email on a daily or weekly basis, and offers the possibility to archive PDF or Powerpoint files, making it available to the scientific community. [ More information ]
Upcoming Seminars  [Next 30 ]  
[ scheduler view ] 
Monday 22 May 2017, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  I will explain how integrability and analyticity can be used to predict certain (fishnet type) Feynman integrals in planar massless $\phi^4$ theory. I will argue, in particular, that they lead to the conjecture that four point fishnet integrals can be written as determinants of ladder integrals. 
Monday 22 May 2017, 14:00 at LPTENS, LPTENS Library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  Holographic models provide unique laboratories to investigate nonlinear physics of transport in inhomogeneous systems. We provide a detailed account of both DC and AC conductivities in a defect conformal field theory with spontaneous stripe order. The spatial symmetry is broken at large chemical potential and the resulting ground state is a combination of a spin and charge density wave. An infinitesimal applied electric field across the stripes will cause the stripes to slide over the underlying density of smeared impurities, a phenomenon which can be associated with the Goldstone mode for the spontaneously broken translation symmetry. 
Monday 22 May 2017, 14:00 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire de Relativité Générale Mathématique )  MATHIHES (TBA)  hepth 



Abstract:  The maximal analytic Schwarzschild spacetime is manifestly inextendible as a Lorentzian manifold with a twice continuously differentiable metric. In this talk I will describe how one proves the stronger statement that the maximal analytic Schwarzschild spacetime is inextendible as a Lorentzian manifold with a continuous metric. The investigation of lowregularity inextendibility criteria is motivated by the strong cosmic censorship conjecture in general relativity. 
Monday 22 May 2017, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  hepth 



Abstract:  : Nous montrerons que, pour de telles représentations ρ : π1Σ → G, l'adhérence de Zariski de ρ(Γ) contient le SL2 principal sauf lorsque Γ est un sousgroupe monogène de π1Σ, auquel cas cette adhérence de Zariski est un sousgroupe abélien régulier connexe. Ceci entraîne la classification des adhérences de Zariski possibles puisque la classification des groupes algébriques contenant le SL2 principal est connue. Enfin dans le cas où Γ = π1Σ (ou un sousgroupe d'indice fini) les paramètres de Hitchin déterminent l'adhérence de ρ(Γ). 
Monday 22 May 2017, 15:30 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire de Relativité Générale Mathématique )  MATHIHES (TBA)  hepth 



Abstract:  We will discuss dynamical properties of the Schwarzschild interior, backwards and forwards (in time) with respect to the initial value problem for the Einstein vacuum equations. 
Monday 22 May 2017, 16:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  hepth 



Abstract:  We investigate the degree to which the geometry of a compact real projective manifold with boundary is reflected in the associated holonomy representation, a representation of the fundamental group in the projective general linear group PGL(n,R) which in general need not have any nice properties. We show that if the projective manifold is strictly convex, then its holonomy representation is projective Anosov, a condition which generalizes the dynamical properties of convex cocompact representations in rank one (e.g. hyperbolic) geometry. Conversely, a strictly convex projective manifold may be constructed from a projective Anosov representation that preserves a properly convex set in projective space. Applications include new examples of both convex projective manifolds and Anosov representations. Joint work with François Guéritaud and Fanny Kassel. 
Tuesday 23 May 2017, 11:00 at LPTHE, LPTHE Library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  I will review some recent developments of type II and heterotic superstring field theory. The approach I will follow is due to Ashoke Sen and based on the construction of the openclosed bosonic string field theory by Zwiebach. Particular attention will be devoted to the three main challenges faced by superstring field theory: inclusion of the Ramond sector, removal of spurious singularities due to the superconformal ghosts and definition of a prescription for the offshell amplitudes. The plan is the following: 1) motivations, divergences in (super)string theory and offshell amplitudes; 2) superstring field theory: gauge fixed and quantum action, construction of the Ramond sector 3) momentum representation of amplitudes, applications: unitarity, soft theorems 
Tuesday 23 May 2017, 14:00 at APC, 454 A  Valentin  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  In the first part of my talk I will discuss the notion of relativity principle, kinematic algebras, the classification of Leblond and Bacry I will define the Carroll group and its extensions. I will gave Applications to very special Relativity String theory and the BMS algebras. In the second part I will discuss plane gravitational waves and how the a subgroup of the Carroll group acts and how this can be used illuminate the currently fashionable topics of gravitational memory and soft gravitons. The talk is aimed at a general audience with a background in Mathematical Physics. 
Tuesday 23 May 2017, 14:30 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  hepth 



Abstract:  A brief survey will be given of the use of KP and 2DToda tau functions of special “hypergeometric type” as generating functions for weighted Hurwitz numbers (i.e. weighted enumerations of Nsheeted branched coverings of the Riemann sphere, or equivalently, weighted paths in the Cayley graph of the symmetric group S_N generated by transpositions). The weights depend on parametric families of auxiliary parameters, and consist of evaluations of basis elements of the algebra of symmetric functions of the latter. An alternative generating function is provided by certain correlation functions W_{n,g}(x_1,. …, x_n) depending on a pair of integers that play a role analogous to the multidifferentials in the Topological Recursion approach to intersection theory on moduli spaced of marked Riemann surfaces. As in that case, an associated invariant classical and quantum “spectral curve” is derived and a set of recursion relations that determine the general term quadratically in terms of finite sums over preceding ones. Examples include: 1) the “simple” (double or single) Hurwitz numbers studied originally by Okounkov and Pandharipande, 2) The case of "Belyi curves”, having just three branch points, one of them weighted, and the related “dessins d’enfants”; 3) The “weakly monotonic” paths in the Cayley graph, for which the generating tau function is the ItzyksonZuberHarishChandra integral and (if time permits) 4) The case of simple "quantum Hurwitz numbers", in which the weighting is shown to coincide with that of a quantum BoseEinstein gas. (Partly based on joint work with M. GuayPaquet, A. Orlov, B. Eynard, A. Alexandrov and G. Chapuy) 
Tuesday 23 May 2017, 16:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  Upcoming cosmological experiments intend to exploit the large scale structure of the Universe to get a better understanding of the observed cosmic acceleration. By measuring the power spectrum, one can constrain the equation of state of dark energy, and galaxy surveys promise great improvement over the current constraints. Galaxy surveys can also be used to gather cosmological information beyond cosmic acceleration. For example, one can derive consistency relations that can relate the bispectrum to the power spectrum for example. Those relations are very robust, as they rely on only two assumptions: the equivalence principle and the gaussianity of initial conditions. They are thus expected to hold within the standard cosmological model. On the other hand, their potential violation can be used to put bound on theories that predict deviations from one of those two assumptions, which is what I will explore in this talk. 
Wednesday 24 May 2017, 14:00 at LPTHE, Bibliothèque  SEMINFOR (Séminaire informel)  hepthmathmathphmath.AGmath.COmath.KTmath.MPmath.QA 



Abstract:  Schubert calculus is a branch of enumerative geometry, which deals with configurations of linear subspaces of a vector space. Translated into the modern language, it amounts to certain calculations in the cohomology ring of Grassmannians and flag varieties. A practical problem is to give a combinatorial rule for the structure constants of that ring. A few years ago, I observed that there was a hidden quantum integrability in the case of Grassmannians (for which the combinatorial rule is the socalled LittlewoodRichardson rule). In a somewhat unrelated development, there has been a growing body of work (including my own) showing the deep connection between cohomology theories (ordinary cohomology, Ktheory, elliptic cohomology) and quantum integrable systems. In particular Maulik and Okounkov introduced a nice framework for this connection. It is natural to try to reinterpret my observation above in this language. After introducing these various concepts, I shall present recent work with A. Knutson in this direction. In particular, this provides completely new rules for the calculation of structure constants of the equivariant cohomology or Ktheory of dstep flag varieties for d smaller or equal to 4, thus moving several "steps" closer to the completion of the program of Schubert calculus. 
Tuesday 30 May 2017, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTSTA (Séminaire de Physique Statistique, CEA/Saclay)  condmat 



Abstract:  Reactive events such as conformation change of macromolecules, chemical reactions in solution, nucleation events during phase transitions, thermally induced magnetization reversal in micromagnets, etc. pose challenges both for computations and modeling. At the simplest level, these events can be characterized as the hopping over a free energy barrier associated with the motion of the system along some reaction coordinate. Indeed this is the picture underlying classical tools such as transition state theory or Kramers reaction rate theory, whose results fit the mathematical framework of the theory of large deviations. These approaches have been successful to explain reactive events in a wide variety of context. However they presuppose that we know or can guess beforehand what the reaction coordinate of the event is. In many systems of interest  protein folding, enzyme kinetics, proteinprotein interactions, etc.  making such educated guesses is hard if not impossible. The question then arises whether we can develop a more general framework to describe reactive events, elucidate their pathway and mechanism, and give a precise meaning to a concept such as the reaction coordinate. In this talk I will discuss recent theoretical advances that have been made in this context, and how they can be used to design efficient algorithms to compute the pathway and rate of reactive events. 
Wednesday 31 May 2017, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Thursday 1 June 2017, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 1 June 2017, 11:00 at IPN, Salle A402  IPNX (Séminaire commun de physique théorique des particules IPNCPHTX)  hepph 



Abstract:  When pions are exchanged almost onshell the range of hadron interactions is unusually long, opening the possibility to interesting phenomena. One example is the Lambda_c(2590) > Sigma_c pi transition, which is mediated by the emission of an Swave pion near the massshell. Other more wellknown example is the D* > D \pi transition, though in this case the pion is in Pwave. When we combine both vertices to obtain the Lambda_c(2590) Dbar > Sigma_c D*bar potential, the result is a longrange inverse square potential. With this potential the Lambda_c(2590) Dbar  Sigma_c D*bar system becomes scale invariant, i.e. it is symmetric under dilatations, a property which is also shared by two and threebody systems with large scattering lengths. This symmetry is however anomalous and is broken by the spectrum, which can at most display a discrete form of it if the interaction is strong enough. We explore where this is the case in the Lambda_c(2590) Dbar  Sigma_c D*bar system, which is a candidate for a molecular explanation of the recently observed heavy pentaquark Pc(4450)+, or in other hadron molecules. In addition we consider what happens when we have a Lambda_c(2590) Sigma_c (or anti Sigma_c) molecule. In this latter case the potential is of the 1/r type, but which an unusual longrange, behaving as Coulomb for typical hadronic scales. The interesting point here is that this coulomblike potential probably holds an Swave shallow state, making for a nice prediction of a nearthreshold hadron molecule. 
Thursday 1 June 2017, 11:45 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 1 June 2017, 13:30 at DPTPHYSENS, room Conf. IV, 24 Rue Lhomond, ENS Paris  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  physics.optics 



Abstract:  In my talk I will discuss the recent exciting developments associated with nonHermitian degeneracies, also known as “exceptional points”. After having been studied mostly in the domain of mathematical physics, quite a number of experiments have recently demonstrated how the presence of exceptional points leads to very counterintuitive effects, such as loss induced lasing, chiral field modes, topological energy transfer etc. I will try to provide an introduction to this topic as well as an overview of the many different areas of physics in which exceptional points are meanwhile being explored. 
Friday 2 June 2017, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/168 )  COURS (Cours)  condmatquantph 



Abstract:  Closed systems (classical or quantum) are always an idealization of reality. A number of techniques of various accuracy and complexity are in use to take into account interactions of the system with its environment. In the crudest non trivial approximation, the effect of the environment is assumed to depend only on the immediate past of the state of the system (i.e. the density matrix in the quantum case), leading to the notion of Markovian open systems. \par In these lectures we motivate the relevance and consistence of the Markovian approximation for open quantum systems. We also show a very deep connection between effects of an environment and effects of repeated indirect measurements. \par We introduce nondemolition measurements and draw some broad conclusions on measurement in quantum mechanics. More generally we use indirect measurements as a tool to scrutinize the evolution of open quantum systems and analyze some properties of quantum trajectories. \par We also introduce the basics of quantum noises. \par Our focus is on properties that are related, or analogous to classical probability theory. We use the discrete time case to introduce the basic concepts, but also make the connection with continuous time systems. \\ \\ Lecture 1: Quick overview of open quantum systems; Brief review of quantum mechanics; Indirect measurements \\ Lecture 2: Discrete quantum Markovian evolution; Non demolition measurements and progressive wave function collapse \\ Lecture 3: From discrete to continuous time: Lindbladian evolution and its stochastic counterpart \\ Lecture 4: Quantum trajectories, quantum jumps \\ Lecture 5: A brief introduction to quantum noises  
Attachments: 
Tuesday 6 June 2017, 11:00 at LPTENS, LPTENS library  SEMLPTENS (Seminaire du LPTENS)  hepth 



Abstract:  String theory on AdS3 is studied from the worldsheet perspective, using the description in terms of a WZW model based on sl(2,R). We identify the leading Regge trajectory states and show that they have the structure of a higher spin Vasiliev theory. We also explain that for the minimal level (corresponding to the situation with a single NS 5brane) the spacetime theory has a stringy tower of massless higher spin fields which are part of a continuum of light states. For the case of AdS3 x S3 x S3 x S1 we use similar techniques to determine the BPS spectrum of the spacetime theory. Our result suggests that the supergravity BPS spectrum is different than previously thought, as we also verify explicitly. This new insight opens the door towards identifying the CFT dual of string theory on this background. 
Tuesday 6 June 2017, 13:30 at
DPTPHYSENS,
room Conf. IV, 24 Rue Lhomond, ENS Paris ( ¡¡ Please be aware of the unusual date: Tuesday !! )  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  condmat.mtrlsci 


Tuesday 6 June 2017, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  I will give an overview of the timescape cosmology. It is assumed that inhomogeneities  voids, walls and filaments  modify the average background geometry of the universe, which is no longer a simple solution of Einstein's equations with homogeneous dust. To obtain a viable phenomenology without dark energy, I provide a framework for interpreting Buchert's backreaction formalism, by revisiting fundamental issues relating to the definition of gravitational energy in a complex geometry. Cosmic acceleration is realized as an apparent effect due both to backreaction and the the relative calibration of the asymptotic clocks of observers in gravitationally bound structures relative to the time parameter that best describes the average statistical evolution. The cosmic coincidence problem is solved directly in relation to the growth of the void fraction. Predictions of the timescape phenomenology are very close to the standard cosmology, but with differences which can be tested. I will outline current observational constraints, future tests (e.g., with the Euclid satellite), and also theoretical challenges that need to be overcome for backreaction models to fully compete with the Lambda Cold Dark Matter cosmology. 
Tuesday 6 June 2017, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 


Wednesday 7 June 2017, 10:30 at LPTENS, Conf IV  COURS (Cours)  grqchepth 


Friday 9 June 2017, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/168 )  COURS (Cours)  condmatquantph 



Abstract:  Closed systems (classical or quantum) are always an idealization of reality. A number of techniques of various accuracy and complexity are in use to take into account interactions of the system with its environment. In the crudest non trivial approximation, the effect of the environment is assumed to depend only on the immediate past of the state of the system (i.e. the density matrix in the quantum case), leading to the notion of Markovian open systems. \par In these lectures we motivate the relevance and consistence of the Markovian approximation for open quantum systems. We also show a very deep connection between effects of an environment and effects of repeated indirect measurements. \par We introduce nondemolition measurements and draw some broad conclusions on measurement in quantum mechanics. More generally we use indirect measurements as a tool to scrutinize the evolution of open quantum systems and analyze some properties of quantum trajectories. \par We also introduce the basics of quantum noises. \par Our focus is on properties that are related, or analogous to classical probability theory. We use the discrete time case to introduce the basic concepts, but also make the connection with continuous time systems. \\ \\ Lecture 1: Quick overview of open quantum systems; Brief review of quantum mechanics; Indirect measurements \\ Lecture 2: Discrete quantum Markovian evolution; Non demolition measurements and progressive wave function collapse \\ Lecture 3: From discrete to continuous time: Lindbladian evolution and its stochastic counterpart \\ Lecture 4: Quantum trajectories, quantum jumps \\ Lecture 5: A brief introduction to quantum noises  
Attachments: 
Friday 9 June 2017, 11:30 at SAMM, C20.13, Centre Pierre MendèsFrance, Univ. Paris1, 90 rue de Tolbiac, Paris  SAMM (Statistics, Analysis, Multidisciplinary Modeling)  condmat.statmechmathphmath.FAmath.MP 



Abstract:  We revisit the instability of solitons in the critical and supercritcal cases of the KdV equation, in particular the fundamental result of MartelMerle about instability of solitary waves for the critical KdV equation. Then we investigate a similar phenomenon in the higher dimensional generalizations of the KdV equation, called the ZakharovKuznetsov equation. This is joint work with Luiz Farah and Justin Holmer. 
Tuesday 13 June 2017, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 


Tuesday 13 June 2017, 16:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  In this talk I present our recent work [1] on simulating the emergence of the Glasma in the early stages of heavy ion collisions in full 3 1 dimensions. Usually, in the color glass condensate framework incoming nuclei are assumed to be infinitely thin Lorentzcontracted pancakes which leads to boostinvariant rapidity profiles of the resulting energy density after the collision. We break boost invariance by allowing for a finite width of the incoming nuclei along the beam direction and obtain Gaussianlike rapidity profiles already at tree level. The profiles resemble strong coupling results and agree surprisingly well with experimental data of pion multiplicities as obtained at RHIC. [1] AI, D. MÃ¼ller, arXiv:1703.00017 
Wednesday 14 June 2017, 10:30 at LPTENS, Conf IV  COURS (Cours)  grqchepth 


Wednesday 14 June 2017, 10:30 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire de Géométrie Arithmétique ParisPékinTokyo )  MATHIHES (TBA)  hepth 


Thursday 15 June 2017, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 



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