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 ]  
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Tuesday 28 March 2017, 10:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours des professeurs permanents de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  In this course, we will present different techniques developed over the past few years, enabling mathematicians to prove that phase transitions are sharp. We will focus on a few classical models of statistical physics, including Bernoulli percolation, the Ising model and the randomcluster model. 
Tuesday 28 March 2017, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  SEMEXCEP (Séminaire exceptionel)  physics 



Abstract:  Au coeur de la matière se trouvent les atomes, au coeur d'un atome se trouve un minuscule noyau, et le noyau de l'atome luimême est constitué de particules qu'on dit "élémentaires" car on les pense indivisibles, les quarks et les gluons. On montrera comment un accélérateur de 27 kilomètres de long permet d'examiner sous toutes les coutures ces particules, et ce qu'apporte la recherche théorique sur ce sujet. 
Tuesday 28 March 2017, 14:00 at LPTM, 4.13 St Martin II  SOUTENTH (Soutenance de thèse)  condmat 



Abstract:  TBA 
Tuesday 28 March 2017, 14:00 at APC, 371 A  Klein (salle inhabituelle)  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  I will summarize the potential of the LISA mission to constrain the expansion history of the universe using massive black hole binary mergers as gravitational wave standard sirens. After briefly reviewing the concept of standard siren, I will outline the analysis and methodologies to use LISA as a cosmological probe, and present estimates for the power of LISA in constraining cosmological parameters for both standard and alternative cosmological models. 
Tuesday 28 March 2017, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  In its original form the Weak Gravity Conjecture (WGC) is a proposed constraint on gauge theories coupled to gravity. From this simple starting point one can however arrive at far reaching implications: if true, the WGC gives rise to severe constraints on models of largefield inflation and it may have important consequences for the stability of the string theory landscape. It is this connection to inflation, which has led to renewed interest in the WGC in the recent years. However, the progress made in this time comes with a price: there exist several competing formulations of the conjecture. Further, there are various generalisations with varying levels of support. While more evidence has been gathered, there is still no proof. In this talk I want to give a status report on the WGC: in particular, I will present the current formulations, recent evidence and the status quo on applications to cosmology and particle physics. 
Tuesday 28 March 2017, 15:30 at LPTHE, bibliothèque  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  The GurauWitten (GW) tensor models provide a field theoretic reformulation of the SachdevYeKitaev model (SYK), with the same fascinating properties. But GW models have in addition a rich randomgeometric content which will be discussed. 
Wednesday 29 March 2017, 11:00 at LPTENS, Conference room 4  SEMLPTENS (Seminaire du LPTENS)  hepth 



Abstract:  We study the fourdimensional low energy effective N=1 supergravity theory of the dimensional reduction of Mtheory on $G_2$manifolds, which are constructed by Kovalev's twisted connected sum gluing suitable pairs of asymptotically cylindrical CalabiYau threefolds $X_{L/R}$ augmented with a circle $S^1$. In the Kovalev limit the Ricciflat $G_2$metrics are approximated by the Ricciflat metrics on $X_{L/R}$ and we identify the universal modulus  the Kovalon  that parametrizes this limit. We observe that the low energy effective theory exhibits in this limit gauge theory sectors with extended supersymmetry. We determine the universal (semiclassical) K\"ahler potential of the effective N=1 supergravity action as a function of the Kovalon and the volume modulus of the $G_2$manifold. This K\"ahler potential fulfills the noscale inequality such that no antideSitter vacua are admitted. We describe geometric degenerations in $X_{L/R}$, which lead to nonAbelian gauge symmetries enhancements with various matter content. Studying the resulting gauge theory branches, we argue that they lead to transitions compatible with the gluing construction and provide many new explicit examples of $G_2$manifolds. (based on 1702.05435 ) 
Thursday 30 March 2017, 11:00 at LPTENS, Library  STRINT (Strings, integrability and beyond)  hepth 



Abstract:  The purpose of renormalisation group and quantum field theory approaches to critical phenomena is to diagonalise the dilatation operator. Its eigenvalues are the critical exponents that determine the power law decay of correlation functions. However, in many realistic situations the dilatation operator is, in fact, not diagonalisable. Examples include geometrical critical phenomena, such as percolation, in which the correlation functions describe fluctuating random interfaces. These situations are described instead by logarithmic (conformal) field theories, in which the powerlaw behavior of correlation functions is modified by logarithms. Such theories can be obtained as limits of ordinary quantum field theories, and the logarithms originate from a resonance phenomenon between two or more operators whose critical exponents collide in the limit. We illustrate this phenomenon on the geometrical Qstate Potts model (FortuinKasteleyn random cluster model), where logarithmic correlation functions arise in any dimension. The amplitudes of the logarithmic terms are universal and can be computed exactly in two dimensions, in fine agreement with numerical checks. In passing we provide a combinatorial classification of bulk operators in the Potts model in any dimension. 
Thursday 30 March 2017, 11:00 at LPTHE, Bibliothèque  SEMINFOR (Séminaire informel)  condmat.statmech 



Abstract:  Pendant mon séminaire j'expliquerai comment on peut décrire, de façon analytique, la convergence du modèle de Kontsevich vers certaines solutions de la hiérarchie de la première équation de Painlevé, et quelle est leur monodromie. Mon outil principale sera la théorie des transformations de Darboux. Ensuite, je discuterai l'universalité (dans le sens de la théorie de matrices aléatoires) de ce modèle. 
Thursday 30 March 2017, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTSTA (Séminaire de Physique Statistique, CEA/Saclay)  condmat 



Abstract:  Equilibrium statistical physics holds true for an ergodic system which loses information of its initial condition by equally exploring all its accessible states under time evolution. In the last decade, a flurry of theoretical work has shown that ergodicity can be broken in an isolated, quantum manybody system even at high energies in the presence of disorder, a phenomena known as manybody localization (MBL). In this talk I will discuss meanfield models for quantum spin glasses and their eigenstate properties. For strong transverse field the system is ergodic and satisfies the eigenstate thermalization hypothesis (ETH), while for weak fields the eigenstates below a critical energy violate ETH. The nonergodic eigenstates at a finite energy density are organized in clusters with distinct magnetization patterns, reminiscent of the clustering transition in spin glass theory. 
Thursday 30 March 2017, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  hepth 



Abstract:  Deformations of cell sheets are ubiquitous in early animal development, often arising from a complex and poorly understood interplay of cell shape changes, division, and migration. In this talk I will describe an approach to understanding such problems based on perhaps the simplest example of cell sheet folding: the “inversion” process of the algal genus Volvox, during which spherical embryos literally turn themselves inside out through a process hypothesized to arise from cell shape changes alone. Through a combination of light sheet microscopy and elasticity theory a quantitative understanding of this process is now emerging. 
Thursday 30 March 2017, 13:30 at DPTPHYSENS, room Conf. IV, 24 Rue Lhomond, ENS Paris  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  condmat 


Thursday 30 March 2017, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  Millions of novel examples of compact G2 holonomy manifolds have been given in recent years as twisted connected sums of asymptotically cylindrical CalabiYau threefolds. For compactifications of type II string theories on such G2 manifolds, we give a construction of their mirrors. Similar to Batyrev's construction of CalabiYau mirrors, pairs of polytopes play a crucial role. 
Thursday 30 March 2017, 14:30 at LPTENS, Library  STRINT (Strings, integrability and beyond)  hepth 



Abstract:  I will describe a new integrable field theory emerging from a strong twist of N=4 SYM and some of its observables like spectrum and correlation functions. I will also point out the emergence of a sector of operators for which the theory becomes a Logarithmic CFT. 
Thursday 30 March 2017, 16:00 at LPT, salle 114, 1er etage, batiment 210  SEMLPT (Séminaire de Physique des Particules du LPT)  hepth 



Abstract:  In this talk, we discuss the implications of the premise that any new, relativistic, highly energetic neutral particle that interacts with quarks and gluons would create cascadelike events in the IceCube (IC) detector which would be observationally indistinguishable from neutral current deepinelastic (DIS) scattering events due to neutrinos. Consequently, one reason for deviations, breaks or excesses in the expected astrophysical powerlaw neutrino spectrum could be the flux of such a particle. Motivated by features in the recent 1347day IceCube high energy starting event (HESE) data, we focus on particular boosted dark matter (\chi) related realizations of this premise, where \chi is assumed to be much lighter than, and the result of, the slow decay of a massive scalar (\phi ) which constitutes a major fraction of the Universe’s dark matter (DM). We show that this hypothesis, coupled with a standard powerlaw astrophysical neutrino flux is capable of providing very good fits to the present data, along with a possible explanation of other features in the HESE sample : ie, a) the paucity of events beyond 2 PeV b) a spectral feature resembling a dip in the 400 TeV  1 PeV region and c) an excess in the 50100 TeV region. We also consider constraints from diffuse gamma ray backgrounds and find that it is indeed very restrictive. 
Thursday 30 March 2017, 16:30 at INSP, 2223 salle 317 au 3ème étage  SEMINSP (Séminaire général de l'INSP)  physicsphysics.atomphphysics.genph 



Abstract:  We have measured several 2S2P transitions in muonic hydrogen ($\mu$p), muonic deuterium ($\mu$d) and muonic helium ions ($\mu^3$He, $\mu^4$He). From muonic hydrogen we extracted a proton charge radius 20 times more precise than obtained from electronproton scattering and hydrogen highprecision laser spectroscopy but at a variance of 7$\sigma$; from these values. This discrepancy is nowadays referred to as the "proton radius puzzle". New insight has been recently provided by the first determination of the deuteron charge radius from laser spectroscopy of $\mu$d. The status of the proton charge radius puzzle including the new insights obtained by $\mu$d spectroscopy will be discussed. 
Friday 31 March 2017, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/166 )  COURS (Cours)  astrophhepth 



Abstract:  Graphs, at their most abstract, provide a language for describing relationships, one which has long been beneficial for the program of physical prediction. Combined with the Wilsonian understanding of effective field theory, perturbative analysis finds a role in predictions relevant to all scales, from processes describing the scattering of primordial gravitons, to QCD interactions at CERN's Large Hadron Collider, to establishing the astrophysical inspiral and consequent postmerger ringing out of black holes, to the evolution of the largest scales cosmologically conceivable. Modern advances in scattering amplitude calculation have reemphasized the role of graphical organization towards efficient prediction, generalizing away from brute Feynman calculation, but yielding structural insights suggestive of a new type of unification touching predictions relevant to all of these scales. \par In these lectures I will talk about graphical organization of perturbative prediction, emphasizing scattering amplitudes, but with an eye towards generalization. \\  GENERALIZED UNITARITY METHODS. How verification can be inverted towards construction. 1 lecture. \\  COLORKINEMATICS (``BCJ'') DUALITY AND ASSOCIATED DOUBLECOPY. Exploring both computational advantages as well as unifying structure exposed. Relevant theories include: Chiral Pions, YangMills, QCD, BornInfeld, VolkovAkulov, Galileons, EinsteinHilbert Gravity, Open and Closed string theories. 2 lectures. \\  QCD. Generalizations particularly relevant to QCD calculations (massive, nonadjoint representations). 1 lecture. \\  GRAVITY/COSMOLOGY. Application of some of these ideas to astrophysical and cosmological classical solutions in gravity. 2 lectures.  
Attachments: 
Monday 3 April 2017, 14:00 at LLR, Salle de séminaires  SEMLLR (Séminaires au Laboratoire LeprinceRinguet)  hepth 



Abstract:  A newly proposed experiment promises to create a “tabletop” black hole that could prove whether information is truly lost when black holes evaporate. The idea that information could be lost this way has created a paradox in our current understanding of basic physics. 43 years ago, Stephen Hawking combined quantum field theory with Einstein’s theory of general relativity and discovered black hole evaporation. The debate over whether information is really lost during Hawking evaporation has persisted ever since. Almost all the contemporary leading theoretical physicists have participated in this “black hole war”. In quantum mechanics, the probability, or information, must be preserved before and after a physical process. The seeming loss of information as a result of the black hole evaporation therefore implies that general relativity and quantum mechanics, the two pillars of modern physics, may be in conflict. 
Tuesday 4 April 2017, 10:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours des professeurs permanents de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  In this course, we will present different techniques developed over the past few years, enabling mathematicians to prove that phase transitions are sharp. We will focus on a few classical models of statistical physics, including Bernoulli percolation, the Ising model and the randomcluster model. 
Tuesday 4 April 2017, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  In the minimal leftright symmetric model which could accommodate the tiny neutrino masses via TeV seesaw mechanism, the neutral scalar from the righthanded symmetry breaking sector could be much lighter than the electroweak scale. We discuss the constraints on this particle from lowenergy flavor observables, e.g. meson oscillations and rare decays, and find that such a light particle is necessarily longlived, and can be searched for at the LHC via displaced signals of a collimated photon jet, if its mass is of order GeV scale. This decay mode provides a new test of TeV scale leftright model. 
Wednesday 5 April 2017, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Thursday 6 April 2017, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  hepth 



Abstract:  The field of "active matter" focuses on the collective behaviour of large numbers of individual units (molecular motors, cells, organisms) which inject energy into a fluid at the small scales, creating largescale nonequilibrium patterns. In this talk I will link together two historically important examples of active matter  concentrated suspensions of bacteria and cytoplasmic streaming in plant and animal cells  to illustrate recent experimental and theoretical developments in the area of selforganization. 
Thursday 6 April 2017, 14:00 at LPT, cosmology room 110, bldg 210, 1st floor  SEMLPT (Séminaire de Physique des Particules du LPT)  hepph 



Abstract:  The space based interferometer LISA has a great potential in probing cosmology. This talk presents two observables through which LISA could provide us with new information on the characteristics of the universe, complementary to what can be gathered from electromagnetic observations : the detection of a stochastic background of gravitational waves coming from the very early universe, and the use of massive black hole binaries as standard sirens to test the expansion of the universe. 
Tuesday 11 April 2017, 10:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours des professeurs permanents de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  In this course, we will present different techniques developed over the past few years, enabling mathematicians to prove that phase transitions are sharp. We will focus on a few classical models of statistical physics, including Bernoulli percolation, the Ising model and the randomcluster model. 
Tuesday 11 April 2017, 10:30 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire de Géométrie Arithmétique ParisPékinTokyo )  MATHIHES (TBA)  hepth 



Abstract:  In order to apply V. Lafforgue's ideas to the study of representations of padic groups, one needs a version of the geometric Satake equivalence in that setting. For the affine Grassmannian defined using the Witt vectors, this has been proven by Zhu. However, one actually needs a version for the affine Grassmannian defined using Fontaine's ring B_dR, and related results on the BeilinsonDrinfeld Grassmannian over a selfproduct of Spa({\mathbb Q}_p). These objects exist as diamonds, and in particular one can make sense of the fusion product in this situation; this is a priori surprising, as it entails colliding two distinct points of Spec({\mathbb Z}). The focus of the talk will be on the geometry of the fusion product, and an analogue of the technically crucial ULA (Universally Locally Acyclic) condition that works in this nonalgebraic setting. 
Tuesday 11 April 2017, 10:30 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire de Géométrie Arithmétique ParisPékinTokyo )  MATHIHES (TBA)  hepth 



Abstract:  In order to apply V. Lafforgue's ideas to the study of representations of padic groups, one needs a version of the geometric Satake equivalence in that setting. For the affine Grassmannian defined using the Witt vectors, this has been proven by Zhu. However, one actually needs a version for the affine Grassmannian defined using Fontaine's ring B_dR, and related results on the BeilinsonDrinfeld Grassmannian over a selfproduct of Spa({\mathbb Q}_p). These objects exist as diamonds, and in particular one can make sense of the fusion product in this situation; this is a priori surprising, as it entails colliding two distinct points of Spec({\mathbb Z}). The focus of the talk will be on the geometry of the fusion product, and an analogue of the technically crucial ULA (Universally Locally Acyclic) condition that works in this nonalgebraic setting. 
Tuesday 11 April 2017, 11:00 at LPTENS, LPTENS Library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  TBA 
Tuesday 11 April 2017, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 


Wednesday 12 April 2017, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Thursday 13 April 2017, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  hepth 



Abstract:  From Leonardo da Vinci to the Brothers Grimm our fascination with hair has endured in art and science. We love it for its “body” or “volume”, the fluffiness and elasticity that comes from its random waves and curls. But apart from a purely tactile response, can we take a more quantitative approach to hair, to explain these macroscopic properties in terms of the behaviour of individual hairs? We know that the important physics governing hair involves the interplay of its elasticity, weight, and curliness, but it is only recently that these have been synthesized into a mathematical theory. This talk will cover those recent advances in the description of physical fiber bundles, including the "Ponytail shape equation" and aspects of "Hairodynamics". 

[ English version ] 