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 ]
[Previous 30 ]  Upcoming Seminars  [Next 30 ] 
[ scheduler view ] 
Monday 11 February 2019, 14:00 at
IAP,
Henri Mineur ( Series of 4 lectures )  COURS (Cours)  grqc 


Tuesday 12 February 2019, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  math 



Abstract:  Flows on surfaces are one of the fundamental examples of dynamical systems, studied since Poincaré; area preserving flows arise from many physical and mathematical examples, such as the Novikov model of electrons in a metal, unfolding of billiards in polygons, pseudoperiodic topology. In this course we will focus on smooth areapreserving or locally Hamiltonian flows and their ergodic properties. The course will be selfcontained, so we will define basic ergodic theory notions as needed and no prior background in the area will be assumed. The course aim is to explain some of the many developments happened in the last decade. These include the full classification of generic mixing properties (mixing, weak mixing, absence of mixing) motivated by a conjecture by Arnold, up to very recent rigidity and disjointness results, which are based on a breakthrough adaptation of ideas originated from Marina Ratner's work on unipotent flows to the context of flows with singularities. We will in particular highlight the role played by shearing as a key geometric mechanism which explains many of the chaotic properties in this setup. A key tool is provided by Diophantine conditions, which, in the context of higher genus surfaces, are imposed through a multidimensional continued fraction algorithm (RauzyVeech induction): we will explain how and why they appear and how they allow to prove quantitative shearing estimates needed to investigate chaotic properties. 
Thursday 14 February 2019, 10:00 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  math 



Abstract:  Flows on surfaces are one of the fundamental examples of dynamical systems, studied since Poincaré; area preserving flows arise from many physical and mathematical examples, such as the Novikov model of electrons in a metal, unfolding of billiards in polygons, pseudoperiodic topology. In this course we will focus on smooth areapreserving or locally Hamiltonian flows and their ergodic properties. The course will be selfcontained, so we will define basic ergodic theory notions as needed and no prior background in the area will be assumed. The course aim is to explain some of the many developments happened in the last decade. These include the full classification of generic mixing properties (mixing, weak mixing, absence of mixing) motivated by a conjecture by Arnold, up to very recent rigidity and disjointness results, which are based on a breakthrough adaptation of ideas originated from Marina Ratner's work on unipotent flows to the context of flows with singularities. We will in particular highlight the role played by shearing as a key geometric mechanism which explains many of the chaotic properties in this setup. A key tool is provided by Diophantine conditions, which, in the context of higher genus surfaces, are imposed through a multidimensional continued fraction algorithm (RauzyVeech induction): we will explain how and why they appear and how they allow to prove quantitative shearing estimates needed to investigate chaotic properties. 
Thursday 14 February 2019, 14:00 at LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  physics.bioph 



Abstract:  Neuronal networks are many particle systems with interesting physical properties: They operate far from thermodynamic equilibrium and show correlated states of collective activity that result from the interaction of large numbers of relatively simple units [1]. We here present recent progress towards a quantitative understanding of such systems by application of nonequilibrium statistical mechanics. Meanfield theory and linear response theory capture many qualitative properties of the "ground state" of recurrent networks [2]. A fundamental quantity required is the single neuron transfer function. Formally, it constitutes an escape problem driven by colored noise. We recently applied boundary layer theory to obtain a reduction to the technically much simpler white noise problem [3]. It allows us, for example, to formulate a theory of finitesize fluctuations in layered neuronal networks [4]. Verification of such theoretical predictions is fundamentally hindered by subsampling: We only see a tiny fraction of all neurons within the living brain at a time. Employing tools from disordered systems (spin glasses) combined with an auxiliary field formulation, we overcome this issue by deriving a meanfield theory that is valid beyond the commonlymade selfaveraging assumption. It predicts that the heterogeneity of the network connectivity enables a novel sort of critical dynamics which unfolds in a lowdimensional subspace [5]. The functional consequences are analyzed by importing tools from field theory of stochastic differential equations. We obtain closedform expressions for the transition to chaos and for the sequential memory capacity of the network by help of replica calculations [6]. We find that cortical networks operate in a hitherto unreported regime that combines instability on short time scales with asymptotically nonchaotic dynamics; a regime which has optimal memory capacity. As an outlook we present two directions in which fieldtheoretical methods enable insights into network dynamics: First, a novel diagrammatic expansion of the effective action around nonGaussian solvable theories [7]; we exemplify this method by finally providing the longsearched for diagrammatic formulation of the ThoulessAndersonPalmer meanfield theory of the Ising model. Second, the application of the functional renormaliztion group to neuronal dynamics [8]. It enables the systematic study of second order phase transitions in such networks. 
Friday 15 February 2019, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/225 )  COURS (Cours)  condmatmathphquantph 



Abstract:  An isolated manybody quantum system is characterized by the absence of any coupling to its environment. According to the laws of quantum mechanics its time evolution is unitary. In spite of this, macroscopic systems are expected to eventually ``relax'' in some way and be amenable to a description by quantum statistical mechanics. Especially in one dimensional systems, the nonequilibrum states often exhibit exotic features. \par In these lectures we will consider some aspects of nonequilibrium time evolution in spin chains. We will mainly focus on integrable systems. More than half of the course will be devoted to the study of the socalled quench dynamics in homogeneous systems; the rest of the course will be on the effects of inhomogeneities, culminating in the description of the socalled generalized hydrodynamic theory. Whenever possible, underlying physical phenomena will be described and explicitly calculated for noninteracting spin chains. Interacting integrable systems will be investigated more qualitatively, pointing out the main effects of the interactions. \par Plan of the lectures: \\ 1) Overview of quench dynamics: meaning of relaxation, integrable vs generic systems. \\ 2) Determination of the local conservation laws in noninteracting spin chain systems and brief overview of the interacting integrable case. \\ 3) Time evolution of the entanglement entropy and relation to the thermodynamic entropy. \\ 4) Overview of the phenomenon of prethermalization in the presence of weak integrabilitybreaking perturbations, and exact study of the intermediate time dynamics in a toy model displaying prerelaxation. \\ 5) Time evolution in inhomogeneous systems; generalized hydrodynamics.  
Attachments: 
Friday 15 February 2019, 11:00 at APC, Amphitheatre Pierre Gilles de Gennes  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  The DiracMilne universe, a matterantimatter universe where antimatter has a negative gravitational mass, presents several elements of concordance with our universe, except apparently for two tests: primordial helium3, and BAO, at least if the latter is interpreted in a conventional way. After a discussion on the definition of a negative mass particle, I will describe the formation of structures in the DiracMilne universe, as well as some additional studies that can be carried out on this model, in order to further test its concordance with our universe. 
Thursday 21 February 2019, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 21 February 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Friday 22 February 2019, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/225 )  COURS (Cours)  condmatmathphquantph 



Abstract:  An isolated manybody quantum system is characterized by the absence of any coupling to its environment. According to the laws of quantum mechanics its time evolution is unitary. In spite of this, macroscopic systems are expected to eventually ``relax'' in some way and be amenable to a description by quantum statistical mechanics. Especially in one dimensional systems, the nonequilibrum states often exhibit exotic features. \par In these lectures we will consider some aspects of nonequilibrium time evolution in spin chains. We will mainly focus on integrable systems. More than half of the course will be devoted to the study of the socalled quench dynamics in homogeneous systems; the rest of the course will be on the effects of inhomogeneities, culminating in the description of the socalled generalized hydrodynamic theory. Whenever possible, underlying physical phenomena will be described and explicitly calculated for noninteracting spin chains. Interacting integrable systems will be investigated more qualitatively, pointing out the main effects of the interactions. \par Plan of the lectures: \\ 1) Overview of quench dynamics: meaning of relaxation, integrable vs generic systems. \\ 2) Determination of the local conservation laws in noninteracting spin chain systems and brief overview of the interacting integrable case. \\ 3) Time evolution of the entanglement entropy and relation to the thermodynamic entropy. \\ 4) Overview of the phenomenon of prethermalization in the presence of weak integrabilitybreaking perturbations, and exact study of the intermediate time dynamics in a toy model displaying prerelaxation. \\ 5) Time evolution in inhomogeneous systems; generalized hydrodynamics.  
Attachments: 
Friday 22 February 2019, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmechhepthmathph 



Abstract:  Floquet topological insulators describe independent electrons on a lattice driven out of equilibrium by a timeperiodic Hamiltonian, beyond the usual adiabatic approximation. In dimension two such systems are characterized by integervalued topological indices associated to the unitary propagator, alternatively in the bulk or at the edge of a sample. In this talk I will give new definitions of the two indices, relying neither on translation invariance nor on averaging, and show that they are equal. In particular disorder and defects are intrinsically taken into account, even in the mobility gap regime. Finally indices can be defined when two driven sample are placed next to one another either in space or in time, and then shown to be equal. The edge index is interpreted as a quantized pumping occurring at the interface with an effective vacuum, and can also be estimated numerically. 
Friday 8 March 2019, 11:00 at APC, Amphitheatre Pierre Gilles de Gennes  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  TBA 
Monday 11 March 2019, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 


Thursday 14 March 2019, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 14 March 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Friday 15 March 2019, 11:00 at APC, Amphitheatre Pierre Gilles de Gennes  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 


Monday 18 March 2019, 14:00 at
IAP,
Henri Mineur ( Series of 5 lectures )  COURS (Cours)  astroph 


Tuesday 19 March 2019, 11:00 at CPHT, Salle de Conference Louis Michel (Bât.6 CPHT)  SEMCPHT (Séminaire du CPHT)  hepth 


Thursday 21 March 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 


Monday 25 March 2019, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 


Monday 25 March 2019, 14:00 at
IAP,
Henri Mineur ( Series of 5 lectures )  COURS (Cours)  astroph 


Thursday 28 March 2019, 11:40 at IHP, 201  RENCTHEO (Rencontres Théoriciennes)  hepth 


Friday 29 March 2019, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmechhepthmathmathphmath.AG 


Monday 1 April 2019, 14:00 at
IAP,
Henri Mineur ( Series of 5 lectures )  COURS (Cours)  grqc 


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


Monday 8 April 2019, 14:00 at
IAP,
Henri Mineur ( Series of 5 lectures )  COURS (Cours)  grqc 


Thursday 11 April 2019, 11:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 11 April 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Monday 15 April 2019, 14:00 at
IAP,
Henri Mineur ( Series of 5 lectures )  COURS (Cours)  grqc 


Wednesday 17 April 2019, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  math 



Abstract:  La conjecture de conservativité affirme qu'un morphisme entre motifs constructibles est un isomorphisme s'il en est ainsi de l'une des ses réalisations classiques (de Rham, $\ell$adique, etc.). Il s'agit d'une conjecture centrale dans la théorie des motifs ayant des conséquences concrètes sur les cycles algébriques. Dans ce cours, on s'intéresse à la conjecture de conservativité en caractéristique nulle et, plus précisément, pour la réalisation de de Rham. L'objectif est double :  D'une part, je parlerai de la tentative de preuve annoncée récemment par l'orateur. L'objectif ici est de décrire suffisamment la structure de l'argument afin d'arriver à l'énoncé problématique et de réaliser l'obstacle qui empêche l'argument d'aboutir.  D'autre part, je parlerai d'une nouvelle stratégie visant à contourner l'énoncé problématique dans l'argument initial. 
Friday 19 April 2019, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  math 



Abstract:  La conjecture de conservativité affirme qu'un morphisme entre motifs constructibles est un isomorphisme s'il en est ainsi de l'une des ses réalisations classiques (de Rham, $\ell$adique, etc.). Il s'agit d'une conjecture centrale dans la théorie des motifs ayant des conséquences concrètes sur les cycles algébriques. Dans ce cours, on s'intéresse à la conjecture de conservativité en caractéristique nulle et, plus précisément, pour la réalisation de de Rham. L'objectif est double :  D'une part, je parlerai de la tentative de preuve annoncée récemment par l'orateur. L'objectif ici est de décrire suffisamment la structure de l'argument afin d'arriver à l'énoncé problématique et de réaliser l'obstacle qui empêche l'argument d'aboutir.  D'autre part, je parlerai d'une nouvelle stratégie visant à contourner l'énoncé problématique dans l'argument initial. 

[ English version ] 