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 ] 
Vendredi 16 Novembre 2018, 11:00 à LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmech 



Abstract:  Conformal field theory (CFT) has been extremely successful in describing universal effects in critical onedimensional (1D) systems, in situations in which the bulk is uniform. However, in many experimental contexts, such as quantum gases in trapping potentials and in several outofequilibrium situations, systems are strongly inhomogeneous. Recently it was shown that the CFT methods can be extended to deal with such 1D situations [1,2]: the system’s inhomogeneity gets reabsorbed in the parameters of the theory, such as the metric, resulting in a CFT in curved space. Here in particular we make use of CFT in curved spacetime to deal with the outofequilibrium situation generated by a frequency quench in a TonksGirardeau gas in a harmonic trap [3]. We show compatibility with known exact result and use this new method to compute new quantities, not explicitly known by means of other methods, such as the dynamical fermionic propagator and the one particle density matrix at different times. REFERENCES: [1] J. Dubail, JM. Stéphan, J. Viti, P. Calabrese, SciPost Phys. 2, 002 (2017). [2] S. Murciano, P. Ruggiero, P. Calabrese, To appear. [3] P. Ruggiero, Y. Brun, J. Dubail, To appear. 
Vendredi 16 Novembre 2018, 14:00 à LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  Current Bphysics data contain two intriguing tensions. First, the LHCb collaboration has reported on some anomalies in bs transitions, with discrepancies with the Standard Model predictions in some angular observables and branching ratios and intriguing hints for lepton universality violation. And second, BaBar, Belle and LHCb have found compatible deviations in observables associated to bc transitions, again hinting at the violation of lepton universality. We will review the proposed explanations for these tensions and focus on new physics models that can simultaneously address both anomalies. In particular, we will discuss gauge extensions of the Standard Model aiming at such goal. 
Vendredi 16 Novembre 2018, 15:00 à LPTMC, Jussieu, tower 1312, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  In this talk, I will present newly developed physicsinspired methods for the solution of counting constraint satisfaction problems (#CSPs). #CSP instances can be reformulated as interacting models whose zerotemperature partition function represents the volume of the solution manifold. I will introduce practical methods to compute such partition functions based on tensor network contraction. In this formulation, computational complexity can be viewed as a manifestation of quantum entanglement, and controlling the growth of entanglement throughout tensor network contraction can yield a significant computation speedup. Using some hard counting problems as benchmarks, I will demonstrate that tensor network methods can be a useful tool for solving some hard classes of #CSPs. I will conclude with an outline of ongoing work on extensions of this framework, such as the simulation of existing and nearterm quantum circuits. 
Lundi 19 Novembre 2018, 10:45 à LPTMC, Jussieu, tower 1312, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  I will discuss a new connection between two different problems: the counting of equilibria of a directed polymer in a random medium (DPRM) and the problem of Anderson localisation for the 1D Schrödinger equation. Using the KacRice formula, it is possible to express the mean number of equilibria of a DPRM in terms of functional determinants. In the onedimensional situation, these functional determinants can be calculated thanks to the GelfandYaglom method, showing that the mean number of equilibria of the DPRM growth exponentially with the length of the polymer, with a rate controlled by the generalized Lyapunov exponent (GLE) of the localisation problem (cumulant generating function of the log of the wave function). The GLE is solution of a spectral problem studied by combining numerical approaches and WKBlike approximation. Furthermore, the formalism can be extended in order to obtain the number of equilibria at fixed energy, providing the (annealed) distribution of the energy density of the line over the equilibria. 
Lundi 19 Novembre 2018, 11:00 à APC, PGG  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  Generally physicists assume that dark matter is a single particle with no interactions in its own sector. We demonstrate that these assumptions are not necessarily true. In particular we show that dark matter can be charged under its own force, even if as light as the weak scale. We furthermore consider the possibility that only a fraction of the dark matter is charged, and can even form a disk inside the Milky Way 
Lundi 19 Novembre 2018, 14:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTSTA (Séminaire de Physique Statistique, CEA/Saclay)  condmat 



Abstract:  The SYK model is a quantum fermionic spin glass model that has been recently recognized as a toy model for holography. At the basis of this is a (quasi) reparametrization symmetry that emerges at low temperature. Interestingly, this symmetry appears also, and for the same reasons, in the dynamics of glasses. An effective theory for reparametrizations has been constructed for SYK, a similar possibility was contemplated years ago for glasses. 
Lundi 19 Novembre 2018, 14:30 à
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  hepth 



Abstract:  The purpose of the talk is to explain a result in collaboration with B. Pozzetti and A. Wienhard expressing the Hausdorff dimension of certain attractors as a critical exponent. This class of attractors consists of limit sets of Anosov representations in PGLd (hence of nonconformal nature) that verify an extra open condition. If time permits, we will discuss implications of the formula to the geometry of the Hitchin component. 
Lundi 19 Novembre 2018, 16:30 à
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  hepth 



Abstract:  Mapping class groups associated to surfaces whose fundamental group is not finitely generated are called "big", and their study is linked to classical problems in dynamics. In this talk, we discuss some of the basic properties of big mapping class groups, their simplicial actions, and how these can be used to prove that big mapping class groups "detect" surfaces or (if time allows) that the space of nontrivial quasimorphisms of a big mapping class group is infinite dimensional. 
Mardi 20 Novembre 2018, 11:00 à CPHT, Salle de conférences Louis Michel, bât. 6  IPNX (Séminaire commun de physique théorique des particules IPNCPHTX)  hepph 



Abstract:  Ever since the discovery of the quarkGluon plasma (QGP) the location of the critical point in the QCD phase diagram  the end point of the firstorder transition between hadron matter and QGP  has been a main research goal for heavyion collison experiments. We use the gauge/gravity duality to study as first a fourdimensional, stronglycoupled gauge theory with a firstorder thermal phase transition. In the dual gauge theory we calculate the evolution and saturation of the spinodal instability. We uncover a new surprising example of the applicability of hydrodynamics to systems with large gradients. We discover with shockwave collisions that in theories with a firstorder phase transition, a longlived, quasistatic state may be formed. 
Mardi 20 Novembre 2018, 11:00 à LPTMS, LPTMS, salle 201, 2ème étage, Bât 100, Campus d'Orsay  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  physics 



Abstract:  We will discuss the properties of a family of integrals involving the cardinal sine fuction, first studied by Borwein & Borwein. The aim is to provide a physicist’s perspective onto a curious change of behaviour occurring within this family, noticed when benchmarking computer algebra packages, and initially attributed to a bug. A number of nontrivial generalizations will be obtained. 
Mardi 20 Novembre 2018, 11:30 à
IPN,
Bâtiment 100, Salle A015 ( $ $ )  IPNTHEO (Séminaire du groupe de physique théorique de l'IPN Orsay)  nuclth 



Abstract:  Nuclear superfluidity is an absolutely fascinating phenomenon: due to a resid ual interaction, two fermion can couple and form a Cooper pair. The formation of the pairs impact macroscopic properties of the system. This was illustrated in the seminal paper of Bohr, Mottelson and Pines, by inspecting the excita tion spectra of eveneven and oddodd nuclei. A lot of theoretical work has been done to investigate pairing correlations and their possible impact on the properties of the nuclear system. Despite such an effort several open questions concerning the underlying structure of the pairing interaction is still unknown. How to improve our knowledge? In my talk, I will focus on the description of pairing properties within Nuclear Energy Density functional theory by illus trating how particular assumptions on the pairing interaction may have large effects on some particular experimental observables. The talk aims at trigger ing a discussion between theory and experiment on future plans on how to tackle such a complicated, but definitely fascinating problem.  
Fichiers attachés: 
Mardi 20 Novembre 2018, 14:00 à APC, 646 A  Mondrian  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  Quantum Chromodynamics, the microscopic theory of strong interaction, is asymptotically free. As a consequence, perturbation theory is a useful tool to study high energy phenomena. In the opposite regime, the infrared, QCD is believed to be nonperturbative. However, last decade lattice simulations have showed that the coupling constant is finite in the infrared and not so big. That makes us think that some features of infrared QCD could be understood using perturbation theory. Moreover, the completely gaugefixed Lagrangian is not known in the infrared. We propose then to use a gaugefixed Lagrangian motivated by lattice simulations and use perturbation theory to study the infrared. We find that the first loop correction for YangMills propagators and vertices reproduces lattice results with great accuracy. In addition, I will present preliminary results for the two loop corrections which confirm the validity of perturbation theory in order to study of YangMills quantities. 
Mardi 20 Novembre 2018, 14:30 à IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  In this talk I will argue that after certain timescale (which scales with the system size as L^{d+2}) dynamics of a local observable becomes universal and it can be described by a random matrix. This talks is based on https://arxiv.org/abs/1804.08626 and other recent works. 
Mardi 20 Novembre 2018, 16:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  Bosonic ultralight dark matter (ULDM) would form cored density distributions at the centre of galaxies. Numerical simulations suggest a scaling relation between the core and the virialised host halo. This prediction lends itself to observational tests, because it implies that the peak circular velocity, measured for the host halo in the outskirts of the galaxy, should approximately repeat itself in the central region. Contrasting this prediction to the measured rotation curves of dozens of wellresolved galaxies, we show that ULDM in the mass range $m\sim (10^{22}\div 10^{21})$~eV, which has been invoked as a possible solution to the smallscale puzzles of $\Lambda$CDM, is in tension with the data. Analysis of the Milky Way inner gravitational potential could probe ULDM up to $m< \sim 10^{19}$~eV. 
Mercredi 21 Novembre 2018, 14:00 à LPTENS, Bibliothèque Joel Scherk  SEMLPTENS (Seminaire du LPTENS)  hepth 



Abstract:  The longrange Ising (LRI) model, defined to have interactions decaying as a power of the distance, undergoes a secondorder phase transition with the critical exponents depending on the strength of this power. The corresponding CFTs, which are nonlocal as they lack a stress tensor, have for many years been advertised as interpolating between a meanfield theory and the shortrange critical Ising model. However, the latter crossover raises conceptual questions due to three properties of the model that can be derived exactly. 1. The LRI has two relevant Z2odd operators. 2. Both of their scaling dimensions are protected. 3. So are the scaling dimensions of oddspin primaries in their OPE. I will describe a recently developed duality which reconciles these facts with what we know about the 2D and 3D Ising models.I will also show how the duality can be used to estimate the critical exponents when the usual WilsonFisher approach is strongly coupled. Finally, I will explain how the numerical bootstrap can be used to corner this model and present the results of a sixcorrelator scan. (basé sur 1810.07199 ) 
Mercredi 21 Novembre 2018, 14:15 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  We consider a 4D theory with a chiral anomaly, on $R^3 \times S^1$. From the 3D perspective, it seems at first that the anomaly is lost since odd dimensions do not allow for local anomalies. However the anomaly cannot simply disappear, and by choosing a regulator that preserves the symmetries of the UV (4D lorentz invariance in this case) in order to integrate out the KKmodes, we show that fielddependant ChernSimons terms are generated at one loop. These are not gauge invariant and in fact capture the whole 4D anomaly, in a 3D language. We further extend these results to 6D anomalies and comment on the implications for Ftheory compactifications. Integrating out the KKmodes also leads infinite distance in radius modulus space. We explain how this relates to the Swampland Distance Conjecture and the idea of emergence. We then apply this to the Ftheory circle and explain how it relates to infinite distances in the Kaehler moduli space of the CalabiYau threefold on which Ftheory is compactified. These singularities can be analyzed from their monodromy matrix, which depends on the intersection number of the CY. This suggests that some topological data of the CY are emergent. 
Mercredi 21 Novembre 2018, 15:00 à
IHES,
Amphithéâtre Léon Motchane ( Séminaire de probabilités et physique statistique de l'IHES )  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  An important conjecture in quantum mechanics is that noninteracting, disordered 3d quantum systems should exhibit a localizationdelocalization transition as a function of the disorder strength. From a mathematical viewpoint, a lot is known about the localized phase for strong disorder, much less about the delocalized phase at weak disorder. In this talk I will present results for a hierarchical supersymmetric model for a class of 3d quantum systems, called Weyl semimetals. We use rigorous renormalization group methods to compute the correlation functions of the system. In particular, I will report a result about the algebraic decay of the averaged twopoint correlation function, compatible with delocalization. Our method is based on a rigorous implementation of RG, reminiscent of the GawedzkiKupiainen block spin transformations; the main technical novelty is the multiscale analysis of Gaussian measures with purely imaginary covariances. Joint work with Luca Fresta and Marcello Porta. 
Mercredi 21 Novembre 2018, 16:30 à
IHES,
Amphithéâtre Léon Motchane ( Séminaire de probabilités et physique statistique de l'IHES )  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  In 1996 Rinat Kashaev introduced a new way to write the startriangle move (or YangBaxter equations) of the Ising model as a single polynomial relation. In 2013 Richard Kenyon and Robin Pemantle understood that this relation could be seen as a kind of spatial recurrence. I will show how the iteration of Kashaev's recurrence can be related the combinatorics of a loop model with two colors, that was introduced for different reasons by Ole Warnaar and Bernard Nienhuis in 1993. It is also possible to couple this loop model with known relatives of the Ising model: a dimer model and a sixvertex model. Finally I will show a few limit shape phenomena. 
Jeudi 22 Novembre 2018, 10:00 à IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  We will analyze the renormalization group (RG) flow of field theories with quenched disorder, in which the couplings vary randomly in space. We analyze both classical (Euclidean) disorder and quantum disorder, emphasizing general properties rather than specific cases. The RG flow of the disorderaveraged theories takes place in the space of their coupling constants and also in the space of distributions for the disordered couplings, and the two mix together. We write down a generalization of the CallanSymanzik equation for the flow of disorderaveraged correlation functions. We find that local operators can mix with the response of the theory to local changes in the disorder distribution, and that the generalized CallanSymanzik equation mixes the disorder averages of several different correlation functions. For classical disorder we show that this can lead to new types of anomalous dimensions and to logarithmic behavior at fixed points. For quantum disorder we find that the RG flow always generates a rescaling of time relative to space, which at a fixed point generically leads to Lifshitz scaling. The dynamical scaling exponent z behaves as an anomalous dimension and we compute it at leading order in perturbation theory in the disorder for a general theory. We also find in quantum disorder that local operators mix with nonlocal (in time) operators under the RG, and that there are critical exponents associated with the disorder distribution that have not previously been discussed. (basé sur 1803.08529 ) 
Jeudi 22 Novembre 2018, 11:00 à IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  A classification will be given of all separable minimal hypersurfaces in $R^{n≥3}$. 
Jeudi 22 Novembre 2018, 11:40 à IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  The horizon conjecture states that all near horizon geometries of extreme black holes that preserve some supersymmetry exhibit an sl(2, R) symmetry. I shall demonstrate the proof of the conjecture in some theories and use it to identify all the Killing superalgebras of near horizon geometries. An application of these results is that there are no near horizon geometries that preserve strictly more than 16 supesymmetries in 10 and 11 dimensions. 
Jeudi 22 Novembre 2018, 14:00 à LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  mathph 



Abstract:  According to the de BroglieBohm pilotwave theory, a quantum system is not only described by its wavefunction, but also by a configuration, which is guided by the wavefunction in a deterministic way (in the case of a non relativistic particle, this configuration is simply a particle position). A quantum ensemble, on the other hand, is described by a wavefunction and by a distribution of configurations. The pilotwave theory reproduces the predictions of standard quantum mechanics for ensembles in which the configurations are distributed according to the Born Law. In principle, the pilotwave theory also allows ensembles in which the configurations are not distributed according to the Born Law: such ensembles are said to be in quantum nonequilibrium and for them standard quantum mechanics is violated, thereby leading to new physics. In the talk, I will give an overview of the pilotwave theory and I will present this idea of quantum nonequilibrium. Then I will show that quantum nonequilibrium can provide an explanation for an anomaly in the data of the Planck satellite mission (it is an anomalous power deficit at large angular scales in the cosmic microwave background spectrum). Finally, I will give an example of the application of the pilotwave approach to simple quantum cosmological models, to show that the existence of a configuration, beside the wavefunction, allows to obtain cosmological scenarios unambiguously (here the example will be that of a bouncing universe with a dark energy phase during its expansion). 
Jeudi 22 Novembre 2018, 16:00 à LPT, 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepth 



Abstract:  The lightcone definition of Parton Distribution Functions (PDFs) does not allow for a direct ab initio determination employing methods of Lattice QCD simulations that naturally take place in Euclidean spacetime. In this presentation we focus on pseudoPDFs where the starting point is the equal time hadronic matrix element with the quark and antiquark fields separated by a finite distance. We focus on Ioffetime distributions, which are functions of the Ioffetime $\nu$, and can be understood as the Fourier transforms of parton distribution functions with respect to the momentum fraction variable $x$. We present lattice results for the case of the nucleon and we also perform a comparison with the pertinent phenomenological determinations. 
Vendredi 23 Novembre 2018, 11:00 à CPHT, Salle de conférences Louis Michel, bât. 6  IPNX (Séminaire commun de physique théorique des particules IPNCPHTX)  hepph 



Abstract:  The lightcone definition of Parton Distribution Functions (PDFs) does not allow for a direct ab initio determination employing methods of Lattice QCD simulations that naturally take place in Euclidean spacetime. In this presentation we focus on pseudoPDFs where the starting point is the equal time hadronic matrix element with the quark and antiquark fields separated by a finite distance. We focus on Ioffetime distributions, which are functions of the Ioffetime $\nu$, and can be understood as the Fourier transforms of parton distribution functions with respect to the momentum fraction variable x. We present lattice results for the case of the nucleon and we also perform a comparison with the pertinent phenomenological determinations. 
Vendredi 23 Novembre 2018, 16:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Mardi 27 Novembre 2018, 11:00 à CPHT, Salle de Conference Louis Michel (Bât.6 CPHT)  SEMCPHT (Séminaire du CPHT)  hepth 



Abstract:  We investigate the space of BPS states in type IIA string theory on a T6 wrapped by one D6 brane and three D2 branes wrapping three disjoint 2 tori. This system of branes has 12 ground states. We show that these 12 states are all recovered as Coulomb branch BPS multicenter bound states, in which each center preserves 16 supercharges. Moreover, we show that these multicenter solutions can only exist with zero angular momentum, supporting the conjecture that all black hole microstates have zero angular momentum. For large charges, they might describe “nearhorizon limit” of fuzzballs. 
Mardi 27 Novembre 2018, 11:00 à LPTMS, LPTMS, salle 201, 2ème étage, Bât 100, Campus d'Orsay  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  physics 



Abstract:  TBA 
Mardi 27 Novembre 2018, 11:30 à LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 


Mardi 27 Novembre 2018, 14:00 à APC, 646 A  Mondrian  APCTH (Seminar of the theory group of APC)  hepth 


Mercredi 28 Novembre 2018, 11:30 à
IPN,
Bâtiment 100, Salle A015 ( $ $ )  IPNTHEO (Séminaire du groupe de physique théorique de l'IPN Orsay)  nuclth 



Abstract:  In this seminar, I will review some recent developments of the Milano group in the study of spinisospin resonances with Skyrme functionals. In the past, different attempts to build a functional that can describe nuclear masses, charge radii and excitation energies of noncharge exchange and charge exchange resonances at the same time have been performed [14]. On this regard, we have proposed in Ref. [5] a new functional named SAMi based on a fitting protocol that allows for a better description of spinisospin resonances without compromising the accuracy in the description of other observables. Subsequently, in Ref. [6] we have further improved the SAMi functional by including tensor terms. For that, we have kept the same fitting protocol of SAMi but including also information from ab initio calculations on neutron and neutronproton drops to determine the tensor terms. The new functional has been named SAMiT. In parallel to the latter work, we have also improved the SAMi functional in the description of the Isobaric Analog State (IAS), a pure isospin resonance. Such improvement has been achieved by the inclusion of isospin symmetry breaking terms to the functional [7]. The new interaction is named SAMiISB. In this case, the SAMi fitting protocol has been extended to also include information on ab initio results of ISB corrections to the symmetric matter equation of state and of the IAS in $^{208}$Pb.\newline [1] N. Giai and H. Sagawa, Phys. Lett. B 106, 379 (1981).\newline [2] P.G. Reinhard, D. J. Dean, W. Nazarewicz, J. Dobaczewski, J. A. Maruhn, and M. R. Strayer, Phys. Rev. C 60, 014316 (1999).\newline [3] N. Paar, T. Niksic, D. Vretenar, and P. Ring, Phys. Rev. C 69, 054303 (2004).\newline [4] H. Liang, N. Van Giai, and J. Meng, Phys. Rev. Lett. 101, 122502 (2008).\newline [5] X. RocaMaza, G. Colò and H. Sagawa, Phys.Rev. C 86, 031306 (2012).\newline [6] Shihang Shen, G. Colò and X. RocaMaza, arXiv:1810.09691 (2018) (Submitted to PRC)\newline [7] X. RocaMaza, G. Colò, and H. Sagawa, Phys. Rev. Lett. 120, 202501 (2018)  
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