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Monday 11 February 2019, 14:00 at IAP, Henri Mineur
( Series of 4 lectures )
COURS (Cours) gr-qc
Cyril Pitrou ( IAP ) Relativistic Boltzmann equation 4

Tuesday 12 February 2019, 14:30 at IHES, Amphithéâtre Léon Motchane
( Cours de l'IHES )
MATH-IHES (TBA) math
Corinna Ulcigrai ( University of Zurich & University of Bristol ) Chaotic Properties of Area Preserving Flows (3/4)
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, pseudo-periodic topology. In this course we will focus on smooth area-preserving -or locally Hamiltonian- flows and their ergodic properties. The course will be self-contained, 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 multi-dimensional continued fraction algorithm (Rauzy-Veech 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 )
MATH-IHES (TBA) math
Corinna Ulcigrai ( University of Zurich & University of Bristol ) Chaotic Properties of Area Preserving Flows (4/4)
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, pseudo-periodic topology. In this course we will focus on smooth area-preserving -or locally Hamiltonian- flows and their ergodic properties. The course will be self-contained, 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 multi-dimensional continued fraction algorithm (Rauzy-Veech 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 SEM-LPTM-UCP (Seminaires du LPTM , Universite de Cergy Pontoise) physics.bio-ph
Moritz Helias ( Institute of Neuroscience and Medicine, Research Centre Jülich, ALLEMAGNE ) Statistical mechanics of correlated neuronal variability
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 non-equilibrium statistical mechanics. Mean-field 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 finite-size fluctuations in layered neuronal networks [4]. Verification of such theoretical predictions is fundamentally hindered by sub-sampling: 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 mean-field theory that is valid beyond the commonly-made self-averaging assumption. It predicts that the heterogeneity of the network connectivity enables a novel sort of critical dynamics which unfolds in a low-dimensional subspace [5]. The functional consequences are analyzed by importing tools from field theory of stochastic differential equations. We obtain closed-form 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 non-chaotic dynamics; a regime which has optimal memory capacity. As an outlook we present two directions in which field-theoretical methods enable insights into network dynamics: First, a novel diagrammatic expansion of the effective action around non-Gaussian solvable theories [7]; we exemplify this method by finally providing the long-searched for diagrammatic formulation of the Thouless-Anderson-Palmer mean-field 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) cond-mat|math-ph|quant-ph
Maurizio Fagotti ( LPTMS ) Quench dynamics and relaxation in isolated integrable quantum spin chains (4/5)
Abstract: An isolated many-body 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 so-called quench dynamics in homogeneous systems; the rest of the course will be on the effects of inhomogeneities, culminating in the description of the so-called 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 pre-thermalization in the presence of weak integrability-breaking perturbations, and exact study of the intermediate time dynamics in a toy model displaying pre-relaxation. \\ 5) Time evolution in inhomogeneous systems; generalized hydrodynamics.
Attachments:
  • 2018_Fagotti.pdf (4422052 bytes) OPEN
  • 2018-2019.pdf (4678999 bytes) OPEN

Friday 15 February 2019, 11:00 at APC, Amphitheatre Pierre Gilles de Gennes APC-COLLOQUIUM (Colloquium de l'APC) astro-ph
Gabriel Chardin ( CNRS/DGDS ) Concordance of the Dirac-Milne universe
Abstract: The Dirac-Milne universe, a matter-antimatter universe where antimatter has a negative gravitational mass, presents several elements of concordance with our universe, except apparently for two tests: primordial helium-3, 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 Dirac-Milne 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 RENC-THEO (Rencontres Théoriciennes) hep-th
Emil Martinec ( University of Chicago ) TBA

Thursday 21 February 2019, 11:40 at IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Irene Valenzuela ( University of Utrecht ) TBA

Friday 22 February 2019, 10:00 at IPHT, Salle Claude Itzykson, Bât. 774
( https://courses.ipht.cnrs.fr/?q=fr/node/225 )
COURS (Cours) cond-mat|math-ph|quant-ph
Maurizio Fagotti ( LPTMS ) Quench dynamics and relaxation in isolated integrable quantum spin chains (5/5)
Abstract: An isolated many-body 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 so-called quench dynamics in homogeneous systems; the rest of the course will be on the effects of inhomogeneities, culminating in the description of the so-called 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 pre-thermalization in the presence of weak integrability-breaking perturbations, and exact study of the intermediate time dynamics in a toy model displaying pre-relaxation. \\ 5) Time evolution in inhomogeneous systems; generalized hydrodynamics.
Attachments:
  • 2018_Fagotti.pdf (4422052 bytes) OPEN
  • 2018-2019.pdf (4678999 bytes) OPEN

Friday 22 February 2019, 11:00 at LPTHE, Bibliothèque SEM-LPTHE (Séminaire du LPTHE) cond-mat.stat-mech|hep-th|math-ph
Clement Tauber ( ETH Zurich ) Bulk-edge correspondence in Floquet topological systems
Abstract: Floquet topological insulators describe independent electrons on a lattice driven out of equilibrium by a time-periodic Hamiltonian, beyond the usual adiabatic approximation. In dimension two such systems are characterized by integer-valued 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 APC-COLLOQUIUM (Colloquium de l'APC) astro-ph
Frederic Vincent ( Obs de Paris ) Event Horizon Telescope Array
Abstract: TBA

Monday 11 March 2019, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774 IPHT-PHM (Séminaire de physique mathématique) math-ph
Sanjay Ramassamy ( ENS (math) ) Dimers and circle patterns

Thursday 14 March 2019, 10:00 at IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Jelle Hartong ( Edinburgh U. ) TBA

Thursday 14 March 2019, 11:40 at IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Joao Penedones ( EPFL, Lausanne ) TBA

Friday 15 March 2019, 11:00 at APC, Amphitheatre Pierre Gilles de Gennes APC-COLLOQUIUM (Colloquium de l'APC) astro-ph
Guenter Sigl ( DESY ) Axion-like particles and possible astrophysical and cosmological signatures

Monday 18 March 2019, 14:00 at IAP, Henri Mineur
( Series of 5 lectures )
COURS (Cours) astro-ph
Cristina Volpe ( APC ) Neutrino Astrophysics 1

Tuesday 19 March 2019, 11:00 at CPHT, Salle de Conference Louis Michel (Bât.6 CPHT) SEM-CPHT (Séminaire du CPHT) hep-th
Davide Cassani TBA

Thursday 21 March 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 13-14, 4eme étage SEM-DARBOUX (Séminaire Darboux - physique théorique et mathématiques) hep-th
Nalini Anantharaman ( IRMA, Strasbourg ) TBA

Monday 25 March 2019, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774 IPHT-PHM (Séminaire de physique mathématique) math-ph
Grégory Schehr ( LPTMS ) Exact persistence exponent for the 2d-diffusion equation and related Kac polynomials

Monday 25 March 2019, 14:00 at IAP, Henri Mineur
( Series of 5 lectures )
COURS (Cours) astro-ph
Cristina Volpe ( APC ) Neutrino Astrophysics 2

Thursday 28 March 2019, 11:40 at IHP, 201 RENC-THEO (Rencontres Théoriciennes) hep-th
Michele Del Zotto ( Durham ) TBA

Friday 29 March 2019, 11:00 at LPTHE, Bibliothèque SEM-LPTHE (Séminaire du LPTHE) cond-mat.stat-mech|hep-th|math|math-ph|math.AG
Sanjay Ramassamy ( ENS Paris ) Dimers and circle patterns

Monday 1 April 2019, 14:00 at IAP, Henri Mineur
( Series of 5 lectures )
COURS (Cours) gr-qc
Cristina Volpe ( APC ) Neutrino Astrophysics 3

Thursday 4 April 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 13-14, 4eme étage SEM-DARBOUX (Séminaire Darboux - physique théorique et mathématiques) hep-th
Nicolas Curien ( Orsay ) TBA

Monday 8 April 2019, 14:00 at IAP, Henri Mineur
( Series of 5 lectures )
COURS (Cours) gr-qc
Cristina Volpe ( APC ) Neutrino Astrophysics 4

Thursday 11 April 2019, 11:00 at IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Hadi Godazgar ( AEI Potsdam ) TBA

Thursday 11 April 2019, 11:40 at IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Tba TBA

Monday 15 April 2019, 14:00 at IAP, Henri Mineur
( Series of 5 lectures )
COURS (Cours) gr-qc
Cristina Volpe ( APC ) Neutrino Astrophysics 5

Wednesday 17 April 2019, 14:30 at IHES, Amphithéâtre Léon Motchane
( Cours de l'IHES )
MATH-IHES (TBA) math
Joseph Ayoub ( Université de Zürich ) Sur la conjecture de conservativité (1/5)
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 )
MATH-IHES (TBA) math
Joseph Ayoub ( Université de Zürich ) Sur la conjecture de conservativité (2/5)
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.

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