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Upcoming Seminars [Next 30 ]
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Friday 22 March 2019, 11:00 at LPTHE, Bibliothèque SEM-LPTHE (Séminaire du LPTHE) cond-mat.stat-mech|hep-th
Stam Nicolis ( Institut Denis Poisson, Tours ) Anisotropic gauge theories: from chiral fermions to new phases of matter
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 Kaluza-Klein 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, non-perturbative, 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 Parisi-Sourlas.

Friday 22 March 2019, 11:00 at IHES, Amphithéâtre Léon Motchane MATH-IHES (TBA) math
Karim Adiprasito ( Hebrew University of Jerusalem & IHES ) Combinatorial Lefschetz Theorems Beyond Positivity
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 Hodge-Riemann relations by a non-degeneracy relation at torus-invariant 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 SEM-EXCEP (Séminaire exceptionel) gr-qc
Norma Sanchez ( LERMA ) New Planckian quantum phase of the Universe before Inflation: Its present day and Dark Energy implications
Abstract: The physical history of the Universe is completed by including the quantum planckian and super-planckian 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 classical-quantum (or wave-particle) 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 13-12 5th floor 5-23 SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée) cond-mat.mes-hall
Fabrice Lemoult ( Institut Langevin, ESPCI ) Introduction de propriétés topologiques dans un métamatériau
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, celle-ci étant beaucoup plus petite que la longueur d'onde de travail. Dans le domaine des micro-ondes, 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'est-à-dire 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 au-delà 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 SEM-EXCEP (Séminaire exceptionel) astro-ph
Pierre Cristofari Where are the PeVatrons?
Abstract: The search for cosmic particle accelerators capable of reaching the PeV ($10^{15}$ eV) range, PeVatrons, is a crucial science target of the very-high-energy (gamma-ray 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 IPHT-PHM (Séminaire de physique mathématique) math-ph
Grégory Schehr ( LPTMS ) Exact persistence exponent for the 2d-diffusion equation and related Kac polynomials

Monday 25 March 2019, 14:00 at IAP, Henri Mineur
( Series of 5 lectures )
COURS (Cours) astro-ph
Cristina Volpe ( APC ) Neutrino Astrophysics 2

Tuesday 26 March 2019, 14:00 at LPTHE, library LPTHE-PPH (Particle Physics at LPTHE) hep-ph|hep-th
Ben Page ( IPhT, Saclay ) Analytics from Numerics: Planar Two-Loop Five-Point QCD Amplitudes
Abstract: Two-loop scattering amplitudes are a vital component in high-precision 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 five-point amplitudes in QCD.

Tuesday 26 March 2019, 15:00 at CPHT, Old Ecole Polytechnique, Amph. Poincaré - 25 rue de la Montagne Sainte-Geneviève SEM-EXCEP (Séminaire exceptionel) hep-th
G. Veneziano, P. Tripathy, R. Leigh, A. Hanany, J. Maharana, J.-P. Derendinger Mini-Workshop Old Ecole Polytechnique
Abstract: 15.00-16.30 session 1 - Gabriele Veneziano: Spontaneous CP breaking in QCD and the axion potential - Prasanta Tripathy: The non-Abelian T-dual of Klebanov-Witten 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? - Jean-Pierre Derendinger: N = 2 to N = 1 with one hypermultiplet

Tuesday 26 March 2019, 16:00 at LPT, 114 LPT-PTH (Particle Theory Seminar of LPT Orsay) hep-ph
Andrei Angelescu ( U. Lincoln Nebraska ) Closing the window on single leptoquark solutions to the B-physics anomalies
Abstract: We examine various scenarios in which the Standard Model is extended by a light leptoquark state to solve for one or both B-physics 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 re-examine in its minimal form, letting it couple only to left-handed 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 FORUM-ENS (Forum de Physique Statistique @ ENS) cond-mat.stat-mech
Manas Kulkarni ( City University of New York - CityTech ) Connections between Classical Integrable Models, Log Gas, and Random Matrix Theory

Thursday 28 March 2019, 10:00 at IHP, 201 RENC-THEO (Rencontres Théoriciennes) hep-th
Gabriele Veneziano ( College de France, CERN ) Soft gravitational radiation from high energy collisions: a progress report
Abstract: I will review recent developments on soft gravitational radiation from ultra-relativistic collisions. Calculations based on recent developments in the eikonal approach and in soft-graviton 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 RENC-THEO (Rencontres Théoriciennes) hep-th
Michele Del Zotto ( Durham ) TBA

Thursday 28 March 2019, 14:00 at LPTM, 4.13 St Martin II SEM-LPTM-UCP (Seminaires du LPTM , Universite de Cergy Pontoise) math-ph
Nikolai Kitanine ( Institut Mathématiques Bourgogne, Université de Bourgogne, Dijon. ) Spin chains: short history of form factors.
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 )
MATH-IHES (TBA) hep-th
Maxim Kontsevitch ( IHES ) Bridgeland Stability over Non-Archimedean Fields (3/4)
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 semi-stable pieces, an analog of Harder-Narasimhan 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 Donaldson-Uhlenbeck-Yau theorem which syas that a holomorphic vector bundle over compact Kaehler manifold is polystable if and only if it admits a metrization satisfying hermitean Yang-Mills equation. In my course I will talk about a non-archimedean analog of analytic Bridgeland stability. I will show several examples, results and conjectures. In particular, I'll introduce non-archimedean moment map equations, generalized honeycomb diagrams, and hypothetical stability on derived categories of coherent sheaves on maximally degenerating varieties over non-archimedean fields.

Thursday 28 March 2019, 16:00 at LPT, 114 LPT-PTH (Particle Theory Seminar of LPT Orsay) hep-ph
Pham Q. Hung ( U. Virginia Charlottesville ) The Lifetime Frontier: Search for New Physics with Long-Lived Particles
Abstract: There is a growing interest in the High Energy community in searching for new physics with long-lived particles which decay at displaced vertices. Many models exhibit this feature. I will describe one of such models : the electroweak-scale non-sterile right-handed neutrino model. In this model, non-sterile right-handed 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 theta-angle of strong CP and neutrino masses will be presented.

Friday 29 March 2019, 11:00 at LPTHE, Bibliothèque SEM-LPTHE (Séminaire du LPTHE) cond-mat.stat-mech|hep-th|math|math-ph|math.AG
Sanjay Ramassamy ( ENS Paris ) Dimers and circle patterns
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 s-embeddings 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 APC-COLLOQUIUM (Colloquium de l'APC) astro-ph
Guenter Sigl ( DESY ) Radio signatures from conversion of axion–like particles to photons
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 13-12 room 5-23 SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée) cond-mat.mes-hall
Kirone Mallick ( IPhT Saclay ) TBA

Monday 1 April 2019, 14:00 at IAP, Henri Mineur
( Series of 5 lectures )
COURS (Cours) gr-qc
Cristina Volpe ( APC ) Neutrino Astrophysics 3

Tuesday 2 April 2019, 14:00 at APC, 646A - Mondrian APC-TH (Seminar of the theory group of APC) gr-qc
Anupam Mazumdar ( Van Swinderen (Institute University of Groningen) ) TBA

Thursday 4 April 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 13-14, 4eme étage SEM-DARBOUX (Séminaire Darboux - physique théorique et mathématiques) hep-th
Nicolas Curien ( Orsay ) TBA

Thursday 4 April 2019, 14:30 at IHES, Amphithéâtre Léon Motchane
( Cours de l'IHES )
MATH-IHES (TBA) hep-th
Maxim Kontsevitch ( IHES ) Bridgeland Stability over Non-Archimedean Fields (4/4)
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 semi-stable pieces, an analog of Harder-Narasimhan 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 Donaldson-Uhlenbeck-Yau theorem which syas that a holomorphic vector bundle over compact Kaehler manifold is polystable if and only if it admits a metrization satisfying hermitean Yang-Mills equation. In my course I will talk about a non-archimedean analog of analytic Bridgeland stability. I will show several examples, results and conjectures. In particular, I'll introduce non-archimedean moment map equations, generalized honeycomb diagrams, and hypothetical stability on derived categories of coherent sheaves on maximally degenerating varieties over non-archimedean fields.

Monday 8 April 2019, 14:00 at IAP, Henri Mineur
( Series of 5 lectures )
COURS (Cours) gr-qc
Cristina Volpe ( APC ) Neutrino Astrophysics 4

Tuesday 9 April 2019, 14:00 at APC, 646A - Mondrian APC-TH (Seminar of the theory group of APC) gr-qc
S Carrozza TBA

Wednesday 10 April 2019, 10:30 at IHES, Centre de conférences Marilyn et James Simons
( Séminaire de Géométrie Arithmétique Paris-Pékin-Tokyo )
MATH-IHES (TBA) math
Zongbin Chen ( Yau Mathematical Sciences Center, Tsinghua University ) The Geometry of the Affine Springer Fibers and Arthur's Weighted Orbital Integrals
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 FORUM-ENS (Forum de Physique Statistique @ ENS) cond-mat.stat-mech
Dmitry Abanin ( University of Geneva ) New non-equilibrium quantum states enabled by breakdown of thermalization

Thursday 11 April 2019, 11:00 at IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Hadi Godazgar ( AEI Potsdam ) TBA

Thursday 11 April 2019, 11:40 at IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Balt Van Rees TBA

Monday 15 April 2019, 10:45 at LPTMC, Jussieu, tower 13-12, room 5-23 SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée) cond-mat.mes-hall
Fabrice Bert ( LPS Orsay ) Quantum spin liquids: an experimental view

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