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Séminaires à venir  [30 suivants]  
[ vue agenda ] 
Mercredi 23 Mai 2018, 09:00 à
LPTM,
Maison internationale de la recherche, NeuvillesurOise. ( The aim of this conference is to contribute to the construction of new approaches to the study of complex problems in each of the involved disciplines. )  WORKCONF (Workshop or Conference)  condmat.disnn 



Abstract:  Sessions: Complex Dynamics I/II: Evolutionary Game Theory, Population Dynamics applied to economic and biological systems. Complexity in social systems; Physical and Mathematical models of complex systems See: https://web.ucergy.fr/complexity2018/ 
Mercredi 23 Mai 2018, 11:30 à
IPN,
Bâtiment 100, Salle A015 ( $ $ )  IPNTHEO (Séminaire du groupe de physique théorique de l'IPN Orsay)  nuclth 



Abstract:  The unitary Fermi gas is a textbook model of strongly correlated fermions that accurately describes ultracoldatom experiments and is also relevant to neutron matter [1]. I will present our longterm project on reliable and accurate computation of equilibrium properties of the unitary Fermi gas by systematic summation of Feynman diagrams. Thanks to a diagrammatic Monte Carlo algorithm, we accurately sample all skeleton diagrams (built on dressed singleparticle and pair propagators) up to order $\sim9$. The diagrammatic series is divergent and there is no small parameter so that a resummation method is needed. Previously we used Abelian resummation methods, which are applicable under the assumption that the diagrammatic series has a nonzero radius of convergence; this led to good agreement with experimental data for the equation of state [2] and Tan's contact [3]. In our more recent work [4], we compute analytically the largeorder asymptotics of the diagrammatic series, and find that even though the radius of convergence is actually zero, the series is resummable by a generalised conformalBorel transformation. Our new data for the equation of state and the contact are consistent with the old ones, but the resummation procedure is now mathematically justified and the error bars are significantly smaller. I will also discuss the computational complexity of diagrammatic Monte Carlo algorithms [5], including the new algorithm of [6]. 1] G. C. Strinati, P. Pieri, G. Roepke, P. Schuck, and M. Urban, Physics Reports 1, 738 (2018) [2] K. Van Houcke, F. Werner, E. Kozik, N. Prokof'ev, B. Svistunov, M. Ku, A. Sommer, L. Cheuk, A. Schirotzek, M. Zwierlein, Nature Phys. 8, 366 (2012) [3] K. Van Houcke, F. Werner, E. Kozik, N. Prokof'ev, B. Svistunov, arXiv:1303.6245 [4] R. Rossi, T. Ohgoe, K. Van Houcke, F. Werner, arXiv:1802.07717 [5] R. Rossi, N. Prokof'ev, B. Svistunov, K. Van Houcke, F. Werner, EPL 118, 10004 (2017) [6] R. Rossi, Phys. Rev. Lett. 119, 045701 (2017)  
Fichiers attachés: 
Jeudi 24 Mai 2018, 11:00 à LPTHE, bibliothèque  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  mathmath.MP 



Abstract:  We will first recall the general framework of cluster algebras and cluster varieties attached to arbitrary quivers. We will then explain what can be said about interesting differential forms on these varieties when the quiver is a tree, and how counting points over finite fields gives a first idea about their cohomology. This will be illustrated with examples, and involve an amusing set of Feynman rules with 3 colors. 
Jeudi 24 Mai 2018, 14:00 à LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  There are some discrepancies with respect to Standard Model predictions in measurements of $b$meson decays. After reviewing the discrepancies and effective field theory fits, we examine simplified models of new physics that may explain a subset of them: in particular, $B \rightarrow K^{(\ast)} \mu^+ \mu^$. There are two such classes of model that explain the discrepancies at treelevel: leptoquarks or $Z^\prime$ models. We then examine the prospects of detecting these two explanations at future colliders: the future circular collider and the high luminosity or high energy versions of the LHC. 
Jeudi 24 Mai 2018, 14:00 à LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  condmat 



Abstract:  The goal of this seminar is to present how spin models are relevant in the physics of quantum simulators through two examples. In the first one, we show that the strong interacting limit of a topological BoseHubbard model with two species maps onto a 2D XY spin model with frustrated couplings on the honeycomb lattice. This model displays an exotic phase thats breaks both parity and time reversal symmetry through the stabilization of a chiral order parameter. While the groundstate remains gapped and the original bosonic model is topological, we find a zero Chern number for the groundstate. In the second example, we discuss how spin models are realized in Rydberg based quantum simulators. We discuss a proposal envisionned by colleagues at College de France and perspectives on some relevant information that could be extracted from the Loschmidt echo. 
Jeudi 24 Mai 2018, 16:00 à LPT, 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  The observed abundance of dark matter can be explained by a thermal relic that annihilates with a weak scale cross section. This socalled “WIMP miracle” points to dark matter masses near the TeV scale. However, dramatic improvements in the sensitivity of direct detection experiments targeting TeV scale dark matter, and the lack of a discovery so far, motivates exploration beyond the WIMP. I will review three wellknown “exceptions” to the WIMP miracle argument: (1) annihilations near a pole, (2) annihilations among multiple channels (“coannihilations”), and (3) annihilations into heavier states (“forbidden channels”). I will argue that forbidden channels and coannihilations are both mechanisms for producing dark matter that is exponentially lighter than the weak scale. I will also introduce a fourth exception, “coscattering,” where the dark matter abundance is produced by inelastic scattering against the thermal bath, instead of annihilations. 
Vendredi 25 Mai 2018, 10:00 à
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/197 )  COURS (Cours)  condmatqbio 



Abstract:  Artificial neural networks, introduced decades ago, are now key tools for automatic learning from data. This series of six lectures will focus on a few neural network architectures used in the context of unsupervised learning, that is, of unlabeled data. \par In particular we will focus on dimensional reduction, feature extraction, and representation building. We will see how statistical physics, in particular the techniques and concepts of random matrix theory and disordered systems, can be used to understand the properties of these algorithms and the phase transitions taking place in their operation. \par Special attention will be devoted to the socalled highdimensional inference setting, where the numbers of data samples and of defining parameters of the neural nets are comparable. The general principles will be illustrated on recent applications to data coming from neuroscience and genomics, highlighting the potentialities of unsupervised learning for biology. \par Some issues: \\  What is unsupervised learning? \\  Hebbian learning for principal component analysis: retardedlearning phase transition and prior information. \\  Bipartite neural nets and representations: autoencoders, restricted Boltzmann machines, Boltzmann machines. \\  Recurrent neural nets: from point to finitedimensional attractors, temporal sequences.  
Fichiers attachés: 
Vendredi 25 Mai 2018, 11:00 à LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmech 



Abstract:  In this talk, I will discuss a theoretical framework for understanding materials that are fragile. These are marginal solids or highly viscous liquids that emerge out of thermal equilibrium in response to external stresses. Granular materials and nonBrownian colloidal suspensions are wellknown examples, however, reconfigurable pathways of force transmission also play an important role in biological systems. In granular materials, external forces such as gravity create rigid and flowing states. The mechanical integrity of these marginal solids is reliant on a filamentary network of stressbearing structures. An outstanding question in the field has been how the constraints of vectorial force balance influence the response of granular assemblies to stress, and create localized stress pathways. I will present results of recent work showing that the localized response is a consequence of the disorder in the underlying contact network, and can be mapped on to a ``localization'' problem. I will also discuss an interpretive theory, based on statistical ensembles, of two transitions driven by frictional contacts: shear jamming and discontinuous shear thickening. 
Lundi 28 Mai 2018, 10:45 à LPTMC, Jussieu, tower 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  The electric double layer is generally viewed as simply the boundary that interpolates between an electrolyte solution and a metal surface. Contrary to that view, recent studies have shown that the interface between ionic liquids and metallic electrodes can exhibit structures and fluctuations that are not simple reflections of surrounding bulk materials [1]. The charge of the electrode is screened by the interfacial fluid and induces subtle changes in its structure, which cannot be captured by the conventional GouyChapman theory. In recent years, this topic has been more intensively addressed in order to develop more efficient supercapacitors [2]. The latter are electrochemical devices that store the charge at the electrode/electrolyte interface through reversible ion adsorption. In order to understand the molecular mechanisms at play, we have performed molecular dynamics simulations on a variety of systems made of ionic liquids and electrodes of different geometries ranging from planar to nanoporous. A key aspect of our simulations is to use a realistic model for the electrodes, by allowing the local charges on the atoms to vary dynamically in response to the electrical potential caused by the ions and molecules in the electrolyte [3]. These simulations have allowed us to gain strong insight on the structure and dynamics of ionic liquids at electrified interfaces. From the comparison between graphite and nanoporous carbidederived carbon (CDC) electrodes, we have elucidated the microscopic mechanism at the origin of the increase of the capacitance enhancement in nanoporous carbons [4]. We have also studied the impact of the carbon texture, by comparing CDC with perforated graphene materials [5]. References: 1. Fedorov, M.V., Kornyshev, A.A., Chem. Rev., 114 (2014), 29783036 2. Salanne, M., Rotenberg, B., Naoi, K., Kaneko, K., Taberna, P.L., Grey, C.P., Dunn, B., Simon, P., Nature Energy, 1 (2016), 16070 3. Merlet, C., Pean, C., Rotenberg, B., Madden, P.A., Simon, P., Salanne, M., J. Phys. Chem. Lett., 4 (2013), 264268 4. Merlet, C., Rotenberg, B., Madden, P.A., Taberna, P.L., Simon, P., Gogotsi, Y., Salanne, M., Nature Materials, 11 (2012), 306310 5. MendezMorales, T., Burbano, M., Haefele, M., Rotenberg, B., Salanne M., J. Chem. Phys., 148 (2018), 193812 
Lundi 28 Mai 2018, 11:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  In this talk I will discuss recent developments in the study of scattering amplitudes in EinsteinYangMills Theory. I will present novel relations between treelevel amplitudes in this theory and YM theory. Finally, I will discuss unitarity based observations regarding rational oneloop amplitudes involving gluons and gravitons. 
Lundi 28 Mai 2018, 14:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTSTA (Séminaire de Physique Statistique, CEA/Saclay)  condmat 



Abstract:  Much much work has been recently devoted to the study of the dynamics of quantum isolated systems after a sudden change in the Hamiltonian. In this talk I will describe the evolution of a family of isolated classical manybody disordered systems after instantaneous quenches of the same kind. The aim of these studies was to disentangle effects due to the quantum/classical nature of the systems from those intimately linked to the isolation and internal interactions (integrability vs. Nonintegrability). I will emphasise the discussion of the dynamic phase diagram and the possible measures reached asymptotically (comparing GibbsBoltzmann equilibrium to Generalised Gibbs Ensemble probabilities). 
Mardi 29 Mai 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:  The realization of twodimensional electronic gases (2DEGs) in oxidebased heterostructures (e.g. LaAlO3/SrTiO3) has led to important discoveries about superconductivity in low dimensions. There have been reports of the observation of pairing interactions without superconductivity (Cheng et al., Nature 521, 196 (2015)) and densityofstates features resembling the pseudogap in cuprates (Richter et al., Nature 502, 528 (2013)). Consequently, this 2DEG has emerged as a model system to study the physics of Cooper pair formation in two dimensions and to gain useful insights about complex problems, e.g., the phase diagram of high temperature superconductors. In this talk, we will discuss about a new method developed in our group for realizing such superconducting systems in oxide heterostructures, and the results of experiments to characterize their properties. Due to the low carrier density, it is possible to change it using a gate voltage following the principle of a fieldeffect transistor. The superconducting critical parameters (temperature and field) are tunable as a function of the gate voltage, leading to a ‘superconducting dome’ in the phase diagram. The possibility of continuously varying the carrier density allows us to study different equilibrium and nonequilibrium features characterizing the electronic phases. Results of some recent experiments will be presented. 
Mardi 29 Mai 2018, 11:30 à LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  Nekrasov and Shatashvili have found a large class of gauge theories in the Omega background, which are dual to some quantum integrable models. Later, the string dual was constructed by Hellerman, Orlando and Reffert in a series of papers. Alternatively, one can also construct the gravity dual of these theories using the gauge/gravity correspondence. In this talk, we will discuss the simplest example, the gravity dual of the 2d N=(2,2)* supersymmetric YangMills (SYM) theory, which can be viewed as the mass deformation of the 2d N=(4,4) SYM theory and is dual to the simplest integrable model, the nonlinear Schrödinger equation. The technique is similar to the construction of the 4d N=2* SYM theory. Eventually, we will identify the mass deformation parameter with the twisted mass and find its counterpart on the gravity side, and we will also see the correspondence between solitons in the integrable model and Dbranes. Possible generalizations to the full NekrasovShatashvili duality will also be discussed. This talk is based on the paper arXiv:1706.09016 and some work in progress. 
Mardi 29 Mai 2018, 14:00 à APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  I will discuss the generalization to pforms of the Galileon idea: to construct the most general theory of an (abelian gauge invariant) pform with (strictly) second order field equations. Such theory have recently be fully classified for spacetime dimension strictly smaller than 12. The covariantization of these theories will also be discussed. 
Mardi 29 Mai 2018, 17:15 à DPTPHYSENS, Jean Jaures (29 rue d'Ulm)  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  physics.bioph 



Abstract:  In many systems we can describe emergent macroscopic behaviors, quantitatively, using models that are much simpler than the underlying microscopic interactions; we understand the success of this simplification through the renormalization group. Could similar simplifications succeed in complex biological systems? I will discuss explicit coarsegraining procedures, analogous to realspace and momentum space RG, that we apply to experimental data on the electrical activity in large populations of neurons in the mouse hippocampus. Probability distributions of coarsegrained variables seem to approach a fixed nonGaussian form, and we see evidence of powerlaw dependencies in both static and dynamic quantities as we vary the coarsegraining scale over two decades. Taken together, these results suggest that the collective behavior of the network is described by a nontrivial fixed point. 
Jeudi 31 Mai 2018, 10:00 à IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Jeudi 31 Mai 2018, 11:45 à IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Vendredi 1 Juin 2018, 10:00 à
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/197 )  COURS (Cours)  condmatqbio 



Abstract:  Artificial neural networks, introduced decades ago, are now key tools for automatic learning from data. This series of six lectures will focus on a few neural network architectures used in the context of unsupervised learning, that is, of unlabeled data. \par In particular we will focus on dimensional reduction, feature extraction, and representation building. We will see how statistical physics, in particular the techniques and concepts of random matrix theory and disordered systems, can be used to understand the properties of these algorithms and the phase transitions taking place in their operation. \par Special attention will be devoted to the socalled highdimensional inference setting, where the numbers of data samples and of defining parameters of the neural nets are comparable. The general principles will be illustrated on recent applications to data coming from neuroscience and genomics, highlighting the potentialities of unsupervised learning for biology. \par Some issues: \\  What is unsupervised learning? \\  Hebbian learning for principal component analysis: retardedlearning phase transition and prior information. \\  Bipartite neural nets and representations: autoencoders, restricted Boltzmann machines, Boltzmann machines. \\  Recurrent neural nets: from point to finitedimensional attractors, temporal sequences.  
Fichiers attachés: 
Lundi 4 Juin 2018, 09:00 à
IPHT,
Amphi Claude Bloch, Bât. 774 ( https://indico.in2p3.fr/event/17044/ )  WORKCONF (Workshop or Conference)  physics 



Abstract:  The 23rd Claude Itzykson Conference, which will take place in the Bloch Amphitheater from June 4 to 6, 2018, is dedicated to our colleague and friend Cirano De Dominicis who was the head and a prominent member of our laboratory for many years. \\ \par The themes of the conference will cover the scientific interests of Cirano: \\ Quantum Systems, \\ Out of Equilibrium Statistical Physics, \\ Disordered Systems and Spin Glasses, \\ Interdisciplinary Systems. \\ \\ \\ The website of the conference is: https://indico.in2p3.fr/event/17044/ \\ \\ Organizing committee: Giulio Biroli, Edouard Brézin, Henri Orland and Laure Sauboy (secretary). \\ \\ Sponsors and benefactors: IPhT (CEA and CNRS), DRF, LabEx LMH. 
Lundi 4 Juin 2018, 10:45 à LPTMC, Jussieu, room 523, 5th floor, tower 1312  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Mardi 5 Juin 2018, 11:30 à LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  TBA 
Mardi 5 Juin 2018, 14:00 à APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 


Mardi 5 Juin 2018, 16:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 


Mercredi 6 Juin 2018, 10:30 à
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire de Géométrie Arithmétique ParisPékinTokyo )  MATHIHES (TBA)  hepth 



Abstract:  Let G be a reductive group over a function field of large enough characteristic. We prove the temperedness at unramified places of automorphic representations of G, subject to a local assumption at one place, stronger than supercuspidality. Such an assumption is necessary, as was first shown by SaitoKurokawa and HowePiatetskiiShapiro in the 70's. Our method relies on the ladic geometry of Bun_G, and on trace formulas. Work with Will Sawin. 
Mercredi 6 Juin 2018, 11:30 à
IPN,
Bâtiment 100, Salle A015 ( $ $ )  IPNTHEO (Séminaire du groupe de physique théorique de l'IPN Orsay)  nuclth 



Abstract:  Since the pioneering work of Robledo [1], the Pfaffian has been extensively studied in nuclear physics. With the use of the Grassmann integrals, his work gives an excellent answer to the signproblem in the overlap between HFB wave functions (Onishi formula [2] proposed in half a century ago). After Robledo's work, I have also studied some extensions [3] and applications. Here I will talk about the following topics: \begin{enumerate} \item Basics of Pfaffian and matrix elements of quantum manybody system \item Pfaffian and signproblem of Onishi formula \begin{itemize} \item Pfaffian formula for overlap of HFB wave functions \item Origin of the signproblem and liked cluster theorem \end{itemize} \item Pfaffian and Wick's theorem \end{enumerate} I will show some examples of Pfaffian in other fields of quantum manybody physics.\\ \newline [1] L.M. Robledo, Phys. Rev. C 79 (2009), 021302(R).\newline [2] N. Onishi, S. Yoshida, Nucl. Phys. 80 (1966) 367.\newline [3] M. Oi, T. Mizusaki, Phys. Lett. B 707 (2012) 305, T. Mizusaki, M. Oi, Phys. Lett. B 715 (2012) 219,T. Mizusaki, M. Oi, F. Chen, Y. Sun, Phys. Lett. B 725 (2013) 175, T.Mizusaki, M.Oi, N.Shimizu, Phys. Lett. B779 (2018) 237.  
Fichiers attachés: 
Mercredi 6 Juin 2018, 14:15 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Vendredi 8 Juin 2018, 10:00 à
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/197 )  COURS (Cours)  condmatqbio 



Abstract:  Artificial neural networks, introduced decades ago, are now key tools for automatic learning from data. This series of six lectures will focus on a few neural network architectures used in the context of unsupervised learning, that is, of unlabeled data. \par In particular we will focus on dimensional reduction, feature extraction, and representation building. We will see how statistical physics, in particular the techniques and concepts of random matrix theory and disordered systems, can be used to understand the properties of these algorithms and the phase transitions taking place in their operation. \par Special attention will be devoted to the socalled highdimensional inference setting, where the numbers of data samples and of defining parameters of the neural nets are comparable. The general principles will be illustrated on recent applications to data coming from neuroscience and genomics, highlighting the potentialities of unsupervised learning for biology. \par Some issues: \\  What is unsupervised learning? \\  Hebbian learning for principal component analysis: retardedlearning phase transition and prior information. \\  Bipartite neural nets and representations: autoencoders, restricted Boltzmann machines, Boltzmann machines. \\  Recurrent neural nets: from point to finitedimensional attractors, temporal sequences.  
Fichiers attachés: 
Vendredi 8 Juin 2018, 14:15 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Lundi 11 Juin 2018, 10:55 à LPTMC, Jussieu, room 523, 5th floor, tower 1312  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Lundi 11 Juin 2018, 11:00 à IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 


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