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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Wednesday 25 April 2018, 10:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  In the `Esquisse d'un programme', Grothendieck proposed studying the action of the absolute Galois group upon the system of profinite fundamental groups of moduli spaces of curves of genus g with n marked points. Around 1990, Ihara, Drinfeld and Deligne independently initiated the study of the unipotent completion of the fundamental group of the projective line with 3 points. It is now known to be motivic by DeligneGoncharov and generates the category of mixed Tate motives over the integers. It is closely related to many classical objects such as polylogarithms and multiple zeta values, and has a wide range of applications from number theory to physics. In the first, geometric, half of this lecture series I will explain how to extend this theory to genus one (which generates the theory in all higher genera). The unipotent fundamental groupoid must be replaced with a notion of relative completion, studied by Hain, which defines an extremely rich system of mixed Hodge structures built out of modular forms. It is closely related to Manin's iterated Eichler integrals, the universal mixed elliptic motives of Hain and Matsumoto, and the elliptic polylogarithms of Beilinson and Levin. The question that I wish to confront is whether relative completion stands a chance of generating all mixed modular motives or not. This is equivalent to studying the action of a `motivic' Galois group upon it, and the question of geometrically constructing all generalised RankinSelberg extensions. In the second, elementary, half of these lectures, which will be mostly independent from the first, I will explain how the relative completion has a realisation in a new class of nonholomorphic modular forms which correspond in a certain sense to mixed motives. These functions are elementary power series in $q$ and $\overline{q}$ and $\log q$ whose coefficients are periods. They are closely related to the theory of modular graph functions in string theory and also intersect with the theory of mock modular forms. 
Wednesday 25 April 2018, 11:30 at
IPN,
Bâtiment 100, Salle A015 ( $ $ )  IPNTHEO (Séminaire du groupe de physique théorique de l'IPN Orsay)  nuclth 



Abstract:  Effective field Theory (EFT) has become the standard protocol in the treatment of the nucleonnucleon interaction. In this talk I will show some recent progress that we have made in a direction that slightly differs from the standard use of chiralEFT to produce potentials employed in few or many body calculations. Starting from the EFT Lagrangian, and passing through the Schroedinger representation, it is possible to reshape the theory in terms of nonrelativistic nucleons coupled to relativistic dynamical pions that occupy momentumlabelled modes in a finite periodic box. We then managed to set up an efficient Quantum Monte Carlo framework to make use of this formulation[1]. Some results on the properties of a single nucleon and of the deuteron will be shown. [1] Lucas Madera, Alessandro Lovato, FP, Kevin E. Schmidt, arXiv:1803.10725  
Attachments: 
Wednesday 25 April 2018, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  I will present the momentum space approach to correlation functions in CFTs based on [1304.7760] and subsequent papers. These techniques lead to simple derivations and representations of conformal 3point functions. Furthermore, I will show how they can be used to elucidate the structure of anomalies and beta functions. 
Wednesday 25 April 2018, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  hepth 



Abstract:  > Complementary series are families of unitary representations of certain semisimple Lie groups and of groups of automorphisms of homogeneous trees. I wil recall their definition for semisimple groups and explain how to prove their existence for groups of automorphisms of trees by a method which allows to extend this construction in order to build new representations of free groups. 
Wednesday 25 April 2018, 16:30 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  hepth 



Abstract:  Among representations of surface groups into Lie groups, the Anosov representations are the ones with the nicest dynamical properties. GuichardWienhard and KapovichLeebPorti have shown that their actions on generalized flag manifolds often admit cocompact domains of discontinuity, whose quotients are closed manifolds carrying interesting geometric structures. Dumas and Sanders studied the topology and the geometry of the quotient in the case of quasiHitchin representations (Anosov representations which are deformations of Hitchin representations). In a conjecture they ask whether these manifolds are homeomorphic to fiber bundles over the surface. In joint work with Qiongling Li, we can prove that the conjecture is true for (quasi)Hitchin representations in SL(n,R) and SL(n,C), acting on projective spaces and partial flag manifolds parametrizing points and hyperplanes. 
Thursday 26 April 2018, 16:00 at LPT, 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  One of the elements needed to understand the observed matterantimatter asymmetry of the universe is violation of time reversal (T). T violation can arise in the Standard Model through operators of dimension four or higher, and generate electric dipole moments of the neutron and light nuclei. I will argue that potential measurements of these EDMs could pinpoint the mechanism(s) of T violation of dimension up to six involving quarks and gluons. 
Wednesday 2 May 2018, 11:00 at LPTMS, Salle Balmer, Laboratoire Aimé Cotton  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  physics.bioph 



Abstract:  Nanodiamond (ND) with Nitrogenvacancy (NV) centers serves as promising biosensor due to its excellent biocompatibility, high photostability, and the long spin coherence time at room temperature. However, the complicated biological environment, e.g. in a single cell, imposes stringent requirements on the sensor probes to be internalized. In this talk, I will discuss the requirements on nanodiamond as intracellular sensor, and the possible strategies that will enable various biosensing measurements. I will start with the understanding of nanodiamondcell interfaces, from anchoring of ND on the plasma membrane to their internalization, and eventually to their intracellular trafficking. Other than the conventional threedimensional trajectories tracking of the ND, it is also possible to track their orientations (rotation), providing additional information of the intracellular environment. One problem with NV based biosensing is that the NV center is less sensitive to certain parameters such as temperature and pressure, and not at all response to many other important biochemical parameters such as pH and nonmagnetic biomolecules. I will also discuss possible schemes of constructing nanodiamond based hybrid sensors, which lead to significantly enhanced sensitivity and/or potentially enable the measurement of various biochemical parameters using NV based quantum sensing. 
Wednesday 2 May 2018, 12:00 at
LPTM,
MIR Neuville 1 rue Descartes, 95000 NeuvillesurOise. ( cf: https://iea.ucergy.fr/fr/manifestations/materiauxmagnetocaloriques.html )  WORKCONF (Workshop or Conference)  condmat 



Abstract:  Il existe actuellement plusieurs raisons pour faire revivre la réfrigération magnétique. D’une part elle reste la méthode préférée pour les applications dans l'espace et elle figure parmi les options pour la réfrigération des aimants supraconducteurs du Futur Collisionneur Circulaire. D'autre part il existe des idées pour améliorer les réfrigérants magnétiques en utilisant les effets coopératifs, comme p.ex. les transitions de phase quantiques induites par un champ magnétique et la frustration géométrique. L’objectif de l'atelier est de proposer une rencontre d'experts français et européens afin d’identifier les perspectives pour des recherches et des applications futures à l'échelle européenne et surtout pour la communauté française. 
Thursday 3 May 2018, 14:00 at LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  mathph 



Abstract:  Les graphes de BarakErdös sont une version orientée acyclique des graphes aléatoires d'ErdösRényi : l'ensemble des sommets est {1,...,n} et pour tout i<j, avec probabilité p on ajoute une arête orientée de i vers j, indépendamment pour chaque paire i<j. La longueur du plus long chemin des graphes de BarakErdös croît linéairement avec le nombre de sommets et le taux de croissance C(p) est une fonction de la probabilité p de présence d'une arête. Foss et Konstantopoulos ont introduit un couplage entre les graphes de BarakErdös et un cas particulier d'un système de particules en interaction appelé modèle infini d'urnes. En utilisant ce couplage, nous verrons que C(p) est analytique pour p>0 et dérivable une fois mais pas deux en p=0. Nous verrons également que les coefficients du développement en série entière de C(p) autour de p=1 sont entiers, suggérant que C(p) est la fonction génératrice d'une classe d'objets combinatoires. 
Friday 4 May 2018, 10:00 at
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.  
Attachments: 
Friday 4 May 2018, 14:00 at LPTHE, Library  P^3 (Particle Physics in Paris)  hepph 



Abstract:  More than twenty one years ago, we predicted that massive primordial black holes (PBH) would form via the gravitational collapse of radiation and matter associated with high peaks in the spectrum of curvature fluctuations, and that they could constitute all of the dark matter today. In 2015, we predicted the clustering and mass distribution of PBH, which peaks at several Msun, and whose highmass tails could be responsible for the seeds of all galaxies. Since then, LIGO has detected gravitational waves from at least five merger events of very massive black hole binaries. We propose that they are PBH, and predict that within a few years a less than one solar mass PBH will be detected by AdvLIGOVIRGO, and that in 10 years, an array of GW detectors (i.e. LIGO, VIRGO, KAGRA, INDIGO, etc.) could be used to determine the mass and spin distribution of PBH dark matter with 10% accuracy. Thus, gravitational wave astronomy could be responsible for a new paradigm shift in the understanding of the nature of dark matter. 
Monday 7 May 2018, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  I will show that a discretization of Virasoro algebra naturally leads to an integrable system which is the Toda chain in the second Hamiltonian structure. After quantization we obtain a qdeformation of the Toda chain which is different from the standard qToda chain. I will present a modular invariant Baxter operator. I will sketch the solution of Baxter equation through the Non Linear Integral Equation technique, yielding modular invariant Bethe equations. 
Wednesday 9 May 2018, 10:30 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire de Géométrie Arithmétique ParisPékinTokyo )  MATHIHES (TBA)  hepth 



Abstract:  We apply the endoscopic classification of automorphic representations for inner forms of unitary groups to bound the growth of cohomology in congruence towers of locally symmetric spaces associated with U(n1,1). Our bound is sharper than the bound predicted by SarnakXue for general locally symmetric spaces. This is joint work with Simon Marshall. 
Wednesday 9 May 2018, 11:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire de Probabilités et de Physique Théorique (organisé par Hugo DuminilCopin et Slava Rychkov) )  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  We present results on the critical behaviour of longrange models of multicomponent ferromagnetic spins and weakly selfavoiding walk in dimensions 1, 2, and 3. The range of the interaction is adjusted so that the models are below their upper critical dimension. Critical exponents are computed for the susceptibility, specific heat, and critical twopoint function, using a renormalisation group method to perturb around a nonGaussian fixed point. This provides a mathematically rigorous version of the epsilon expansion. 
Monday 14 May 2018, 10:45 at LPTMC, Jussieu, tower 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Tuesday 15 May 2018, 10:00 at
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.  
Attachments: 
Tuesday 15 May 2018, 11:30 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  TBA 
Tuesday 15 May 2018, 17:15 at DPTPHYSENS, Jean Jaures (29 rue d'Ulm)  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  condmat 



Abstract:  TBA 
Wednesday 16 May 2018, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  We will discuss toroidal compactifications of the bosonic and heterotic strings, focusing on the phenomenon of symmetry enhancement arising at selfdual points in moduli space. I will present the effective action describing the low energy effective theory close to the points of enhancement, obtained from string theory scattering amplitudes, show how symmetry breaking arises naturally as a Higgs mechanism, and show that this action can be obtained from a suitable (twisted) SherkSchwarz reduction of double field theory. 
Friday 18 May 2018, 10:00 at
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.  
Attachments: 
Tuesday 22 May 2018, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTGEN (Séminaire général du SPhT)  physics 


Tuesday 22 May 2018, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 


Wednesday 23 May 2018, 09:00 at
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/ 
Thursday 24 May 2018, 11:00 at LPTHE, bibliothèque  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  mathmath.MP 


Friday 25 May 2018, 10:00 at
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.  
Attachments: 
Friday 25 May 2018, 11:00 at 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. 
Monday 28 May 2018, 10:45 at LPTMC, Jussieu, tower 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Tuesday 29 May 2018, 11:30 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  TBA 
Tuesday 29 May 2018, 14:00 at 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. 
Tuesday 29 May 2018, 17:15 at DPTPHYSENS, Jean Jaures (29 rue d'Ulm)  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  physics.bioph 



Abstract:  TBA 

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