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 ] 
Friday 22 March 2019, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmechhepth 



Abstract:  We review the effect of introducing anisotropic couplings for lattice gauge theories and show that these can lead to new, ``layered'', phases, beyond the bulk confining and Coulomb phases, known in abelian gauge theories. The new phases can be interpreted as describing the effects of flux compactifications and generalize the KaluzaKlein paradigm of extra dimensions. Extra dimensions have been, in fact, used to describe defects in condensed matter systems and anisotropic gauge theories can be also understood as allowing the description of more elaborate defects. Coupling matter to the gauge fields leads to a consistent, nonperturbative, description of chiral fermions, provided the anomalies are properly cancelled, and can describe edge states and their currents while scalar fields lead to a quite elaborate phase diagram. The challenges of assembling these ingredients to study supersymmetric theories will be touched on, as a way of describing how such systems can be consistently closed, a la ParisiSourlas. 
Friday 22 March 2019, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  math 



Abstract:  Consider a simplicial complex that allows for an embedding into R^d. How many faces of dimension d/2or higher can it have? How dense can they be? This basic question goes back to Descartes' "Lost Theorem" and Euler's work on polyhedra. Using it and other fundamental combinatorial problems, we introduce a version of the Kähler package beyond positivity, allowing us to prove the hard Lefschetz theorem for toric varieties (and beyond) even when the ample cone is empty. A particular focus lies on replacing the HodgeRiemann relations by a nondegeneracy relation at torusinvariant subspaces, allowing us to state and prove a generalization of theorems of Hall and Laman in the setting of toric varieties and, more generally, the face rings of Hochster, Reisner and Stanley. This has several applications including full characterization of the possible face numbers of simplicial rational homology spheres, a generalization of the crossing lemma.) 
Friday 22 March 2019, 14:00 at OBSPARIS, Salle de l'atelier, 77 Av. Denfert Rochereau, Paris 14e  SEMEXCEP (Séminaire exceptionel)  grqc 



Abstract:  The physical history of the Universe is completed by including the quantum planckian and superplanckian phase before Inflation in the Standard Model of the Universe in agreement with observations. In the absence of a complete quantum theory of gravity, we start from quantum physics and its foundational milestone: the universal classicalquantum (or waveparticle) duality, which we extend to gravity and the Planck domain. A new quantum precursor phase of the Universe appears beyond the Planck scale. Relevant cosmological examples as the Cosmic Microwave Background, Inflation and Dark Energy have their precursors in this era. A whole unifying picture for the Universe epochs and their quantum precursors emerges with the cosmological constant as the vacuum energy, entropy and temperature of the Universe, clarifying the so called cosmological constant problem which once more in its rich history needed to be revised. The consequences for the deep universe surveys, and missions like Euclid will be outlined. 
Monday 25 March 2019, 10:45 at LPTMC, Jussieu tower 1312 5th floor 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  Les métamatériaux sont des milieux artificiels qui offrent des propriétés de propagation exotiques, comme par exemple des effets de réfraction négative. Ces effets sont la conséquence de l’interaction des ondes avec la cellule unité composant ces métamatériaux, celleci étant beaucoup plus petite que la longueur d'onde de travail. Dans le domaine des microondes, un exemple de cellule unité est une simple tige métallique placée sur un plan de masse, et dans le cas de l’acoustique une simple canette de soda jouant le rôle de résonateur de Helmholtz. Dans un milieu composé de nombreuses cellules unités, la propagation de l'onde est décrite simplement avec le modèle du polariton, c'estàdire par une relation de dispersion résultant de l'hybridation de l'onde et de la résonance individuelle de chaque résonateur. Dans cet exposé, nous montrerons comment aller audelà de cette description habituelle permet d’introduire des propriétés topologiques à la propagation des ondes. 
Monday 25 March 2019, 11:00 at IAP, Evry Schatzman  SEMEXCEP (Séminaire exceptionel)  astroph 



Abstract:  The search for cosmic particle accelerators capable of reaching the PeV ($10^{15}$ eV) range, PeVatrons, is a crucial science target of the veryhighenergy (gammaray domain $\sim$ TeV= $10^{12}$ eV) community. Such accelerators are essential in the context of the problem of the origin of Galactic cosmic rays, and more generally, in order to understand the physical mechanisms involved in the production of PeV particles. Subsequent to the acceleration of PeV particles, the production of gamma rays in the 100 TeV range is expected. Explorations in this energy domain are thus natural in the search for PeVatrons, where gamma—ray instruments are already accumulating data. Relying on Monte Carlo simulations, we explore the capabilities of current instruments to identify the most promising candidates. 
Monday 25 March 2019, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 


Monday 25 March 2019, 14:00 at
IAP,
Henri Mineur ( Series of 5 lectures )  COURS (Cours)  astroph 


Tuesday 26 March 2019, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepphhepth 



Abstract:  Twoloop scattering amplitudes are a vital component in highprecision cross section calculations at the LHC. At higher multiplicities, the increased number of scales can make the algebra of analytic amplitude calculations intractable. In this talk, we discuss how to apply numerical techniques to sidestep this intermediate complexity and combine them with physical properties of the amplitude to efficiently determine its analytic form. In particular we focus on planar fivepoint amplitudes in QCD. 
Tuesday 26 March 2019, 15:00 at CPHT, Old Ecole Polytechnique, Amph. Poincaré  25 rue de la Montagne SainteGeneviève  SEMEXCEP (Séminaire exceptionel)  hepth 



Abstract:  15.0016.30 session 1  Gabriele Veneziano: Spontaneous CP breaking in QCD and the axion potential  Prasanta Tripathy: The nonAbelian Tdual of KlebanovWitten background and its Penrose limits  Rob Leigh 17:00  18:30 session 2  Amihay Hanany: Magnetic quivers  Jnan Maharana: Is the scattering amplitude analytic in field theory with a compact spatial coordinate?  JeanPierre Derendinger: N = 2 to N = 1 with one hypermultiplet 
Tuesday 26 March 2019, 16:00 at LPT, 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  We examine various scenarios in which the Standard Model is extended by a light leptoquark state to solve for one or both Bphysics anomalies, namely RK, or RD(*). To do so, we combine the constraints arising from low–energy observables and from direct searches at the LHC, showing that none of the scalar leptoquarks of mass mLQ ~ 1 TeV can, by itself, simultaneously accommodate both of the above mentioned anomalies. The only single leptoquark scenario which can provide a viable solution for mLQ ~ 1 TeV is a vector leptoquark, known as U1, which we reexamine in its minimal form, letting it couple only to lefthanded fermions. We discuss how the limits deduced from LHC direct searches are complementary to the low–energy physics constraints. Focusing on lepton flavor violating b > sll modes, we show that improving the experimental upper bound on Br(B > K mu tau) by two orders of magnitude could compromise the minimal U1 model as a viable solution to the B physics anomalies. 
Wednesday 27 March 2019, 12:00 at LPENS, Conf IV  FORUMENS (Forum de Physique Statistique @ ENS)  condmat.statmech 


Thursday 28 March 2019, 10:00 at IHP, 201  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  I will review recent developments on soft gravitational radiation from ultrarelativistic collisions. Calculations based on recent developments in the eikonal approach and in softgraviton theorems can be successfully compared in their common region of applicability. Combining the results of both approaches leads to a knee in the spectrum at a typical "Hawking frequency” and to a bump at wavelengths comparable to the impact parameter of the collision. 
Thursday 28 March 2019, 11:40 at IHP, 201  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 28 March 2019, 14:00 at LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  mathph 



Abstract:  The computation of form factors for the spin chains has always been one of the most important problems of the theory of quantum integrable systems. It gained even more importance when it was shown that the dynamical structure factors can be computed using explicit analytic representations for the form factors and these numerical results give extremely good predictions for neutron scattering experiments. It was also recently demonstrated that the form factor analysis leads to a very powerful method of asymptotic computation of the correlation functions and dynamical structure factors. In this talk I’ll review these recent developments and introduce the lqtest results on the form factors in the thermodynamic limit of the spin chains in zero magnetic field. 
Thursday 28 March 2019, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  Bridgeland stability structure/condition on a triangulated category is a vast generalization of the notion of an ample line bunlde (or polarization) in algebraic geometry. The origin of the notion lies in string theory, and is applicable to derived categories of coherent sheaves, quiver representations and Fukaya categories. In a category with Bridgeland stability every objects carries a canonical filtration with semistable pieces, an analog of HarderNarasimhan filtration. It is expected that for categories over complex numbers Bridgeland stability structures often admit analytic enhancements, similar to the relation between ample bundles and usual Kaehler metrics. In a sense, this should be a generalization DonaldsonUhlenbeckYau theorem which syas that a holomorphic vector bundle over compact Kaehler manifold is polystable if and only if it admits a metrization satisfying hermitean YangMills equation. In my course I will talk about a nonarchimedean analog of analytic Bridgeland stability. I will show several examples, results and conjectures. In particular, I'll introduce nonarchimedean moment map equations, generalized honeycomb diagrams, and hypothetical stability on derived categories of coherent sheaves on maximally degenerating varieties over nonarchimedean fields. 
Thursday 28 March 2019, 16:00 at LPT, 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  There is a growing interest in the High Energy community in searching for new physics with longlived particles which decay at displaced vertices. Many models exhibit this feature. I will describe one of such models : the electroweakscale nonsterile righthanded neutrino model. In this model, nonsterile righthanded neutrinos as well as other "mirror" quarks and leptons can be produced at the LHC and their decay products in the form of standard model particles appear at displaced vertices. A deep connection between the thetaangle of strong CP and neutrino masses will be presented. 
Friday 29 March 2019, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmechhepthmathmathphmath.AG 



Abstract:  The dimer model is a model from statistical mechanics corresponding to random perfect matchings on graphs. Circle patterns are a class of embeddings of planar graphs such that every face admits a circumcircle. In this talk I describe a correspondence between dimer models on planar bipartite graphs and circle pattern embeddings of these graphs. As special cases of this correspondence we recover the Tutte embeddings for resistor networks and the sembeddings for Ising models. This correspondence is also the key for studying Miquel dynamics, a discrete integrable system on circle patterns. 
Friday 29 March 2019, 11:00 at APC, Amphitheatre Pierre Gilles de Gennes  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  Axion–like particles (ALPs) can convert into photons in several different ways: in an external magnetic field (known as the Primakoff effect), by decay into two photons, or through parametric amplification of incoming radio photons in an oscillating ALP field within a narrow frequency range. For non–relativistic ALPs all three effects can give rise to radio lines, in particular from astrophysical objects with strong magnetic fields or from regions with ALP over–densities, such as ALP stars. I will give an overview over estimated intensities and prospects for detectability of such radio lines. 
Monday 1 April 2019, 10:45 at LPTMC, Jussieu tower 1312 room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Monday 1 April 2019, 14:00 at
IAP,
Henri Mineur ( Series of 5 lectures )  COURS (Cours)  grqc 


Tuesday 2 April 2019, 14:00 at APC, 646A  Mondrian  APCTH (Seminar of the theory group of APC)  grqc 


Thursday 4 April 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 


Thursday 4 April 2019, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  Bridgeland stability structure/condition on a triangulated category is a vast generalization of the notion of an ample line bunlde (or polarization) in algebraic geometry. The origin of the notion lies in string theory, and is applicable to derived categories of coherent sheaves, quiver representations and Fukaya categories. In a category with Bridgeland stability every objects carries a canonical filtration with semistable pieces, an analog of HarderNarasimhan filtration. It is expected that for categories over complex numbers Bridgeland stability structures often admit analytic enhancements, similar to the relation between ample bundles and usual Kaehler metrics. In a sense, this should be a generalization DonaldsonUhlenbeckYau theorem which syas that a holomorphic vector bundle over compact Kaehler manifold is polystable if and only if it admits a metrization satisfying hermitean YangMills equation. In my course I will talk about a nonarchimedean analog of analytic Bridgeland stability. I will show several examples, results and conjectures. In particular, I'll introduce nonarchimedean moment map equations, generalized honeycomb diagrams, and hypothetical stability on derived categories of coherent sheaves on maximally degenerating varieties over nonarchimedean fields. 
Monday 8 April 2019, 14:00 at
IAP,
Henri Mineur ( Series of 5 lectures )  COURS (Cours)  grqc 


Tuesday 9 April 2019, 14:00 at APC, 646A  Mondrian  APCTH (Seminar of the theory group of APC)  grqc 


Wednesday 10 April 2019, 10:30 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire de Géométrie Arithmétique ParisPékinTokyo )  MATHIHES (TBA)  math 



Abstract:  The affine Springer fibers are geometric objects conceived for the study of orbital integrals. They have complicated geometric structures. We will explain our work on the geometry of affine Springer fibers, with emphasize on the construction of a fundamental domain, and show how the study of the affine Springer fibers can be reduced to that of its fundamental domain. As an application, we will explain how to calculate Arthur's weighted orbital integrals via counting points on the fundamental domain. 
Wednesday 10 April 2019, 12:00 at LPENS, Conf IV  FORUMENS (Forum de Physique Statistique @ ENS)  condmat.statmech 


Thursday 11 April 2019, 11:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 11 April 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Monday 15 April 2019, 10:45 at LPTMC, Jussieu, tower 1312, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



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