The SEMPARIS seminar webserver hosts annoucements of all seminars taking place in Paris area, in all topics of physics, mathematics and computer science. It allows registered users to receive a selection of announcements by email on a daily or weekly basis, and offers the possibility to archive PDF or Powerpoint files, making it available to the scientific community. [ More information ]
Upcoming Seminars  [Next 30 ]  
[ scheduler view ] 
Friday 22 November 2019, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/245 https://www.ipht.fr/Phocea/Vie\_des\_labos/Seminaires/index.php?id=993959 )  COURS (Cours)  condmat 



Abstract:  In this series of lectures we will give a broad view of topological systems, including topological insulators, quantum Hall effect, and topological superconductors. We will discuss the properties of Majorana states and other topological edge states in both onedimensional and twodimensional systems, as well as the techniques to study the formation of these states and their properties. \par Integer and fractional quantum Hall effects will be discussed notably using the composite fermion contruction of wavefunctions. We will describe fractional charge and statistics of the quantum Hall states and their effective field theoretic description. The pfaffian state proposed to describe the elusive $\nu =5/2$ state will be also decribed.\\ The program of the lectures will include: \\ 1 Topology in solid state systems; Examples of topological materials and topological edge states (e.g. Majorana) \\ 2 Analytical and numerical techniques to derive the formation of edge states \\ 3 2D electronic systems, Landau levels, integer and fractional quantum Hall effect \\ 4 The Laughlin wavefunction, more fractions composite fermions \\ 5 Multicomponent systems: spins and interlayer phase coherence, quantum Hall ferromagnetism \\ 6 The pfaffian state and its excitations.  
Attachments: 
Friday 22 November 2019, 14:00 at LPTENS, Bibliotheque Joel Scherk  LPTENSHE (Séminaire commun LPTENSLPTHE)  hepth 



Abstract:  I show some aspects of conformal field theories at finite temperature in momentum space. First I provide a formula for the Fourier transform of a thermal conformal block and study its analytic properties. In particular I show that the Fourier transform vanishes when the conformal dimension and spin are those of a "double twist" operator $\Delta = 2\Delta_\phi + \ell + 2n$. I present a simple example to illustrate this property. Then, by analytically continuing to Lorentzian signature, I show that the spectral density at high spatial momenta has support on the spectrum condition $\omega > k$. This leads to a series of sum rules. 
Friday 22 November 2019, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  In this talk I will discuss our recent work on time dependent dynamics for theories with a first order phase transition using a holographic description. I will make a brief review of our previous work on holographic phase separation which leads to a couple of questions. In particular I will analyze the collisions and merging of domains of different phases, boost invariant evolution and some conclusions for the future study of the dynamics of a confinementdeconfinement transition. 
Monday 25 November 2019, 10:30 at
IHES,
Centre de conférences Marilyn et James Simons ( NokiaIHES Workshop )  MATHIHES (TBA)  hepth 



Abstract:  Approximating highdimensional functionals with lowdimensional models is a central issue of machine learning, image processing, physics and mathematics. Deep convolutional networks are able to approximate such functionals over a wide range of applications. This talk shows that these computational architectures take advantage of scale separation, symmetries and sparse representations. We introduce simplified architectures which can be anlalyzed mathematically. Scale separations is performed with wavelets and scale interactions are captured through phase coherence. We show applications to image classificaiton and generation as well as regression of quantum molecular energies and modelization of turbulence flows. 
Monday 25 November 2019, 10:45 at LPTMC, Jussieu, tower 1312, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  Quantum walks are versatile toy models for periodically driven systems in the nonperturbative regime of lowfrequency and highintensity drive. In this regime, systems can have "hidden" topological invariants: they can host topologically protected edge states even if their effective Hamiltonian is topologically trivial. I will discuss schemes we developed [1,2] to measure the bulk topological invariants, including the "hidden" ones, directly, which also work in the case with spatial disorder, and which have recently been measured in quantum walk experiments[3,4]. [1]: T Rakovszky, JK Asbóth, A Alberti: Detecting topological invariants in chiral symmetric insulators via losses, Phys Rev B 95 (20), 201407 [2]: B Tarasinski, JK Asbóth, JP Dahlhaus: Scattering theory of topological phases in discretetime quantum walks, Phys Rev A 89 (4), 042327 [3]: Zhan, X., Xiao, L., Bian, Z., Wang, K., Qiu, X., Sanders, B.C., Yi, W. and Xue, P.: Detecting topological invariants in nonunitary discretetime quantum walks. Phys Rev Lett, 119(13), 130501 [4]: S Barkhofen, T Nitsche, F Elster, L Lorz, A Gábris, I Jex, C Silberhorn: Measuring topological invariants in disordered discretetime quantum walks, Phys Rev A 96 (3), 033846 
Monday 25 November 2019, 11:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://www.ipht.fr/Phocea/Vie_des_labos/Seminaires/index.php?id=993973 )  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  In the world of elliptic integrability Inozemtsev's spin chain is quite a strange bird: this model of longrangeinteracting electrons with elliptic interactions links the Heisenberg XXX spin chain, the HaldaneShastry spin chain and the elliptic CSM model and is exactly solvable, but whether it is integrable remains an open question.In its current form the solution of this elliptic spin chain looks complicated and does not promote further investigation. In an effort to change this, I will present a reparametrisation of this solution in the form of an extended Bethe ansatz that simplifies things considerably: most importantly, I will show that the Mparticle energy can be written in (quasi)additive form and the Bethe ansatz equations can be written in a familiar form. Moreover, written in the right variables the spectral problem becomes fully rational. 
Monday 25 November 2019, 11:30 at
IHES,
Centre de conférences Marilyn et James Simons ( NokiaIHES Workshop )  MATHIHES (TBA)  hepth 



Abstract:  Endtoend learning is one of the most promising applications of machine learning for the physical layer of communication systems. I will provide a tutorial introduction to the topic and will discuss recent results as well as future research direction. 
Monday 25 November 2019, 13:30 at LPENS, Conf IV  LPA (Séminaire du laboratoire Pierre Aigrain)  condmat 



Abstract:  Helical edge states in topological insulators and semiconducting nanowires are attracting a tremendous amount of attention due to the prospect of inducing and manipulating Majorana states in superconducting hybrid devices. However, most of the topological systems studied so far for Majorana physics remain obscured by material issues such as bulk parasitic bulk conduction or inhomogeneous chemical potential. In this talk I will present a new type of topological insulator constructed on the basis of the quantum Hall effect of graphene. I will show that the ground state of charge neutral graphene under perpendicular magnetic field is a quantum Hall topological insulator with a ferromagnetic order that exhibits spinfiltered, helical edge channels. The topological phase emerges in the graphene zeroth Landau level via a suitable screening of the Coulomb interaction by a SrTiO3 highk dielectric substrate. We observed robust helical edge transport emerging at a magnetic field as low as 1 T and withstanding temperatures up to 110 K over micronlong distances. This new and versatile graphene platform opens up a promising avenue for topological superconductivity. 
Monday 25 November 2019, 14:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTSTA (Séminaire de Physique Statistique, CEA/Saclay)  condmat 



Abstract:  A typical quench experiment consists of a sudden release of a cold atomic gas from an optical lattice. The local properties of the quench dynamics have been extensively studied, however the global properties of this nonequilibrium quantum systems have received less attention. Here we study some aspects of global nonequilibrium behavior by calculating the amount of work done by the quench as measured through the work distribution function. Using Bethe Ansatz techniques we determine the Loschmidt echo and from it the work distribution function of a gas of bosons initially held in a deep periodic potential and subsequently either the potential is completely removed (process described by the LiebLiniger model) or lowered (process described by the SineGordon model). We find the average work and its universal edge exponents at threshold and determine the long time decay of the Loshcmidt echo. We highlight striking differences caused by the interactions as well as the changes in the geometry of the system. We study repulsive as well as attractive interactions. In particular we examine the prominent role played by bound states in the work distribution and show that, with low probability, they allow for negative work to be extracted from the quench. 
Monday 25 November 2019, 14:00 at
IHES,
Centre de conférences Marilyn et James Simons ( NokiaIHES Workshop )  MATHIHES (TBA)  hepth 



Abstract:  We make the case that over the coming decade, computer assisted reasoning will become far more widely used in the mathematical sciences. This includes interactive and automatic theorem verification, symbolic algebra, and emerging technologies such as formal knowledge repositories, semantic search and intelligent textbooks. After a short review of the state of the art, we survey directions where we expect progress, such as mathematical search and formal abstracts, developments in computational mathematics, integration of computation into textbooks, and organizing and verifying large calculations and proofs. For each we try to identify the barriers and potential solutions. 
Monday 25 November 2019, 15:00 at
IHES,
Centre de conférences Marilyn et James Simons ( NokiaIHES Workshop )  MATHIHES (TBA)  hepth 



Abstract:  We will first give a quick review of how information theory impacts AI, in particular how a complex system can evolve into a more complex system while satisfying the laws of information theory. Second we will investigate the problem of learnability. Deep neural networks are sometimes uncapable of learning surprisingly simple problems, we will try to hint a characterization of those problems. 
Tuesday 26 November 2019, 11:00 at CPHT, Salle Louis Michel, CPHT, Ecole Polytechnique  SEMCPHT (Séminaire du CPHT)  hepth 



Abstract:  I will explore a surprising interplay between fundamental principles underlying scattering amplitudes: gauge invariance, IR and UV behavior, the colorkinematics duality, locality and unitarity. Surprisingly, unexpected combinations of these principles have unique solutions: the tree level scattering amplitudes of important massless theories. Two consequences stand out: the emergence of unitarity from other principles, and the possibility of an IR/UV duality. 
Tuesday 26 November 2019, 11:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://www.ipht.fr/Phocea/Vie_des_labos/Seminaires/index.php?id=993975 )  IPHTGEN (Séminaire général du SPhT)  physics 



Abstract:  Optimal transport (OT) has become a discipline by itself that offers solutions to a wide range of theoretical problems in probability and mathematics. Despite its appealing theoretical properties, solving the OT problem involves the resolution of a linear program whose computational cost can quickly become prohibitive whenever the size of the problem exceeds a few hundred points. The recent introduction of entropy regularization, however, has led to the development of fast algorithms for solving an approximate OT problem. The successes of those algorithms have resulted in a popularization of the applications of OT in several applied fields such as imaging sciences and machine learning, and in data sciences in general. Problems remain, however, as to the numerical convergence of those regularized approximations towards the actual OT solution. In addition, the physical meaning of this regularization is unclear. In this talk, I will describe a novel approach to solving the discrete balanced and unbalanced OT problems using techniques adapted from statistical physics. I will illustrate applications of this framework to the problem of image comparison as well as to the problem of comparing three dimensional shapes. 
Tuesday 26 November 2019, 11:30 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  According to holographic subregion duality, the reduced CFT state on a boundary subregion is dual to the subregion's bulk entanglement wedge, and viceversa. In sufficiently high dimensions, one can construct settings in which minimal 2surfaces that are anchored to a given boundary subregion can reach parametrically far beyond the entanglement wedge. In particular, knowledge of the areas of all such 2surfaces is sufficient to reconstruct the bulk metric in the region that they probe, and, in certain settings, these minimal 2surface areas can be deduced from the expectation values of Wilson loops in the boundary subregion. This suggests that either the reduced CFT state encodes significant information about the bulk beyond the entanglement wedge, challenging conventional intuition about holographic subregion duality, or that the geometric computation of Wilson loop expectation values breaks down, even in very mild settings. 
Tuesday 26 November 2019, 14:00 at CPHT, Salle Louis Michel, CPHT  SEMCPHT (Séminaire du CPHT)  hepth 



Abstract:  Generalised global symmetries are a generic feature of theories with topologically conserved charges. For certain physical theories, these allow for an entirely symmetry based reformulation of the lowenergy physics in the hydrodynamic regime without making reference to the specific microscopics. In this talk, we will introduce some of these ideas in the concrete setting of magnetohydrodynamics (MHD), seen as a fluid with conserved "strings" (magnetic field lines). We will argue that MHD is described by a novel theory of superfluidity with a partially broken oneform symmetry. Time permitting, we will also comment on another application of generalised global symmetries to the theory of viscoelasticity. The talk is based on [1808.01939, 1811.04913, 1908.01175]. 
Tuesday 26 November 2019, 14:00 at APC, 646A  Mondrian  APCTH (Seminar of the theory group of APC)  grqc 



Abstract:  In this talk we will review some selected modified theories of gravity and study their cosmological and astrophysical implications. In particular, we investigate the quasinormal modes (QNMs) for black hole solutions in the following modified gravity theories: the Palatini f(R) gravity, the EiBI gravity, a class of nonsingular black holes which can be treated as the vacuum solution of a family of conformal gravity theories, and the generalized energy momentum squared gravity. The master equations describing the QNMs are derived, and the QNM frequencies are evaluated with the WentzelKramers Brillouin (WKB) method and the eikonal approximation. As expected, the QNM spectra of these modified black holes would deviate from their GR counterparts, indicating the possibility of testing these black hole solutions with the help of future gravitational wave detections. 
Tuesday 26 November 2019, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 


Tuesday 26 November 2019, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  In this talk, I first review the role of affine Yangian (AY) to prove AGT conjecture. I emphasize that the duality in the representation plays an essential role to prove the conjecture. I also explain that the connection with the integrability as the name of the algebra suggests. In the second part, if the time permits, I would like to explain my recent work on the corner vertex operator algebra. Some emphasis is put on the connection with the plane partition realization of the minimal models. 
Wednesday 27 November 2019, 11:30 at LPTENS, Scherk library (formerly LPTENS library)  SEMEXCEP (Séminaire exceptionel)  grqc 


Wednesday 27 November 2019, 14:00 at LPENS, L363/365  LPA (Séminaire du laboratoire Pierre Aigrain)  condmat 


Wednesday 27 November 2019, 14:15 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://www.ipht.fr/Phocea/Vie_des_labos/Seminaires/index.php?id=993968 )  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  In the last couple of years it has been proposed that the BekensteinHawking entropy of rotating AdS$_d$ black holes ($4 \leq d \leq 7$) can be reproduced by extremizing the Legendre transform of a homogeneous function of chemical potentials subject to a complex constraint. In this seminar, I will provide a physical interpretation of these extremization principles, showing that in each dimension the entropy function coincides with the onshell supergravity action when the BPS chemical potentials are obtained by taking a specific BPS limit of black hole thermodynamics. To perform the limit, one starts from finite temperature and reaches the extremal BPS black hole along a supersymmetric trajectory in the space of complexified solutions. We thus provide a generalization of the BPS limit proposed in [arXiv:1810.11442] to multicharge black holes and to every dimension $d$. 
Thursday 28 November 2019, 09:30 at LPENS, L361  LPA (Séminaire du laboratoire Pierre Aigrain)  condmat 


Thursday 28 November 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepthmath 


Thursday 28 November 2019, 16:00 at LPT, 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  The observed muon anomalous magnetic moment deviates from the Standard Model predictions at the level of 4 sigma. The discrepancy can be explained by the presence of New Physics. The simplest explanation assumes the existence of new scalar or gauge bosons. As an example of new scalars we consider scalar leptoquark contributions. In particular, a mechanism that calls for mixing of two scalar leptoquarks of the same electric charge through the interaction with the Higgs field, where the two leptoquarks separately couple to the quarkmuon pairs of opposite chirality structures. Another example is a gauge boson which arrises in the U(1) extension of the SM. The parameter space of such a Z’ model is strongly constrained by the discrepancy between experimental result and theoretical prediction for the muon anomalous magnetic moment. 
Friday 29 November 2019, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/245 https://www.ipht.fr/Phocea/Vie_des_labos/Seminaires/index.php?id=993960 )  COURS (Cours)  condmat 



Abstract:  In this series of lectures we will give a broad view of topological systems, including topological insulators, quantum Hall effect, and topological superconductors. We will discuss the properties of Majorana states and other topological edge states in both onedimensional and twodimensional systems, as well as the techniques to study the formation of these states and their properties. \par Integer and fractional quantum Hall effects will be discussed notably using the composite fermion contruction of wavefunctions. We will describe fractional charge and statistics of the quantum Hall states and their effective field theoretic description. The pfaffian state proposed to describe the elusive $\nu =5/2$ state will be also decribed.\\ The program of the lectures will include: \\ 1 Topology in solid state systems; Examples of topological materials and topological edge states (e.g. Majorana) \\ 2 Analytical and numerical techniques to derive the formation of edge states \\ 3 2D electronic systems, Landau levels, integer and fractional quantum Hall effect \\ 4 The Laughlin wavefunction, more fractions composite fermions \\ 5 Multicomponent systems: spins and interlayer phase coherence, quantum Hall ferromagnetism \\ 6 The pfaffian state and its excitations.  
Attachments: 
Friday 29 November 2019, 11:30 at APC, Amphithéâtre Pierre Gilles de Gennes  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  The LIGO/Virgo gravitational wave detections, the imaging of a black hole shadow by long baseline radio interferometry, and ever more precise observations across all electromagnetic wavelengths have opened an unprecedented window onto gravity at its strongest. Black holes are the simplest, most compact, and physically elusive macroscopic objects in the Universe and play a central role in this new era in physics and astronomy. In this talk, I will describe how black holes can be used to understand foundational questions: are gravitons massless? Are black holes the simplest possible macroscopic objects? do event horizons and black holes really exist, or is their formation halted by some asyet unknown mechanism? Do singularities arise in our universe as the outcome of violent collisions? Can black holes inform us about the nature of the elusive dark matter? 
Friday 29 November 2019, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 


Monday 2 December 2019, 10:00 at IPHT, Amphi Claude Bloch, Bât. 774  SOUTENHDR (Soutenance d'Habilitation à Diriger des Recherches)  physics 



Abstract:  L'exposé présentera quelques aspects du mémoire d'habilitation, qui est luimême une synthèse des travaux de recherche que j'ai effectués entre 2005 et 2019. Le mémoire s'organise en quatre chapitres. Les trois premiers portent sur les cartes planaires aléatoires. Le chapitre 1 s'intéresse à leurs propriétés métriques : à partir d'une bijection générale entre cartes et mobiles, on calcule la fonction à trois points des quadrangulations, avant d'évoquer le lien avec les fractions continues. Le chapitre 2 présente la décomposition en tranches, une approche bijective unifiée qui s'applique notamment aux cartes irréductibles. Le chapitre 3 a pour sujet le modèle de boucles O(n) sur les cartes planaires : par une décomposition combinatoire récursive on obtient le diagramme de phase, puis on étudie les statistiques d'emboîtements entre boucles. Le chapitre 4 porte quant à lui sur les partitions aléatoires et processus de Schur, en allant des pavages de dominos pentus aux systèmes fermioniques. 
Monday 2 December 2019, 10:45 at LPTMC, campus Jussieu, tower 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Monday 2 December 2019, 13:30 at LPENS, Conf IV  LPA (Séminaire du laboratoire Pierre Aigrain)  condmat 



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