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 ] 
Tuesday 22 January 2019, 11:00 at LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  mathph 



Abstract:  I will discuss the spontaneous emergence of some complex collective dynamics in networked phase oscillators. As a first step, I will discuss how synchronization can be set in the system. Synchronization is a process in which dynamical systems adjust some properties of their trajectories (due to their interactions, or to a driving force) so that they eventually operate in a collective and macroscopically coherent way. A common result is that the vast majority of transitions to synchronization are of the secondorder type, continuous and reversible. However, as soon as networked units with complex architectures of interaction are taken into consideration, abrupt and irreversible phenomena may emerge, namely explosive synchronization, which rather remind firstorder like transitions. In the second part of my talk, I will try to concentrate on a novel coherent state, the Bellerophon state, which is generically observed in the proximity of explosive synchronization at intermediate values of the coupling strength. Bellerophon states are multiclustered states emerging in symmetric pairs. In these states, oscillators belonging to a given cluster are not locked in their instantaneous phases or frequencies, rather they display the same longtime average frequency (a sort of effective global frequency). Moreover, Bellerophon states feature quantum traits, in that such average frequencies are all odd multiples of a fundamental frequency. Finally, I will show a way to generalize the concept of interdependence of graphs when dynamical systems are considered to be the constituents of the networks, and in relationship to the setting of collective dynamics. 
Tuesday 22 January 2019, 14:00 at APC, 646 A  Mondrian  APCTH (Seminar of the theory group of APC)  grqc 



Abstract:  I will explain how primordial black holes can form from perturbations seeded during inflation and how their abundance can be calculated in the framework of stochastic inflation. This formalism incorporates quantum backreaction of the smallwavelength fluctuations on the large distances dynamics of the Universe. If quantum corrections are small, the probability distribution of density fluctuations is well approximated by a Gaussian. If they are large, the PDF has a different profile with a longer tail and leads to constraints different from the ones usually derived. I will also discuss the validity of the stochastic formalism beyond the usual slowroll approximation, and how, if at all, it must be modified in such regimes. 
Tuesday 22 January 2019, 16:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  We study chemical equilibration in outofequilibrium QuarkGluon Plasma using the first principle method of QCD effective kinetic theory, accurate at weak coupling. In longitudinally expanding systemsrelevant for relativistic nuclear collisionswe find that for realistic couplings chemical equilibration takes place after hydrodynamization, but well before local thermalization. We estimate that hadronic collisions with final state multiplicities $dNch/d \eta > \sim 102$ live long enough to reach approximate chemical equilibrium, which is consistent with the saturation of strangeness enhancement observed in protonproton, protonnucleus and nucleusnucleus collisions. \\ \\ References: arXiv:1811.03040, arXiv:1811.03068 
Wednesday 23 January 2019, 11:30 at
IPN,
Bâtiment 100, Salle A015 ( $ $ )  IPNTHEO (Séminaire du groupe de physique théorique de l'IPN Orsay)  nuclth 



Abstract:  Ultracold atomic Fermi gases have been widely studied from both theoretical and experimental point of view during the last decades. In the low density regime, the twobody interaction between the constituents is well described by the leading order of the $s$wave scattering channel and can be fine tuned from weak to strong coupling by applying an external magnetic field. Such systems are remarkable laboratories to test and design manybody theories. In particular, the low density limit of strong coupling for which the $s$wave scattering length $a_s$ is infinite, namely the unitary gas limit, has recently received a special and growing interest in nuclear physics due to the presence of anomalously large scattering length $a_s \sim 20~\text{fm}^{1}$. Especially the perturbation expansion of observables fails for density $\rho \gtrsim 10^{7} \rho_0$ where $\rho_0$ is the saturation density. Resummation techniques have been investigated in Effective Field Theory (EFT) framework for infinite matter by summing up all orders in perturbation of a certain class of Feynman diagrams to describe properties of strongly interacting Fermi systems. These resummations result in compact expressions of the energy as a function of low energy constants and density. The aim of this work is to propose a nonempirical density functional theory for ultracold atoms based on resummation techniques keeping the information on the interaction. In this presentation, I will first introduce resummation theory for ultracold atoms and present simplified density functionals obtained describing remarkably well the thermodynamic properties of Fermi gas from small scattering length to unitarity. Then I will discuss the possibility to use resummation for the selfenergy that encodes the quasiparticle properties. I will show, as an illustration, the resummed effective mass and effective potential extracted from the selfenergy and discuss the link with Landau Fermi liquid theory and perspectives for density functional approaches.  
Attachments: 
Wednesday 23 January 2019, 14:30 at IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  mathph 



Abstract:  I will describe a remarkable symmetric monoidal category associated to a reductive group G, which acts centrally on any Gcategory. This construction quantizes the universal centralizer group scheme, together with its action on Hamiltonian Gspaces used by Ngo in his proof of the Fundamental Lemma. The category and its central action appear most naturally in a Langlands dual incarnation, which is phrased in terms of convolution on the affine Grassmannian, via work of Bezrukavnikov, Finkelberg and Mirkovic. This is joint work with David BenZvi. 
Thursday 24 January 2019, 10:00 at
LPTHE,
bibliothèque du LPTHE, tour 1314, 4ème étage ( Attention, lieu inhabituel ! )  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  We will analyze the renormalization group (RG) flow of field theories with quenched disorder, in which the couplings vary randomly in space. We analyze both classical (Euclidean) disorder and quantum disorder, emphasizing general properties rather than specific cases. The RG flow of the disorderaveraged theories takes place in the space of their coupling constants and also in the space of distributions for the disordered couplings, and the two mix together. We write down a generalization of the CallanSymanzik equation for the flow of disorderaveraged correlation functions. We find that local operators can mix with the response of the theory to local changes in the disorder distribution, and that the generalized CallanSymanzik equation mixes the disorder averages of several different correlation functions. For classical disorder we show that this can lead to new types of anomalous dimensions and to logarithmic behavior at fixed points. For quantum disorder we find that the RG flow always generates a rescaling of time relative to space, which at a fixed point generically leads to Lifshitz scaling. The dynamical scaling exponent z behaves as an anomalous dimension and we compute it at leading order in perturbation theory in the disorder for a general theory. We also find in quantum disorder that local operators mix with nonlocal (in time) operators under the RG, and that there are critical exponents associated with the disorder distribution that have not previously been discussed. (based on 1803.08534 ) 
Thursday 24 January 2019, 11:40 at
LPTHE,
bibliothèque du LPTHE, tour 1314, 4eme étage ( Attention, lieu inhabituel ! )  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  Finding de Sitter compactifications of string theory has long been a challenge. They are known to require quantum corrections, or orientifold planes, or both. Most existing models rely on effective fourdimensional actions, or work with the tendimensional action but involve 'smearing' the internal Oplanes. After a brief review of such efforts, we present some new numerical solutions with localized and backreacted O8planes. While the solution is singular and stronglycoupled near one of the O8s, it exhibits the same behavior observed for such objects in flat space and in a variety of AdS solutions in various dimensions, with solid holographic crosschecks. Away from the O8s the solution can be made parametrically weaklycoupled thanks to some moduli, whose nature might however be changed by string theory corrections. 
Thursday 24 January 2019, 14:00 at LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  CoRR.NI 



Abstract:  Social networks are a powerful tool for studying complex social processes such as opinion formation, influence and persuasion. This phenomena are important not only for grasping a better understanding of communication in society but also for explaining some of the current threats to democracy and consensus. In fact, the processes that contribute to group formation, as homophily and social reinforcement are the same that produce echo chambers that can threaten diversity and induce the adoption of extreme positions and speech polarization. The electoral period constitutes an excellent case study to investigate the consequences of social structure for democracy and political debate. In this work we analyze 54M tweets involving 300,000 users, captured during the last Argentinian presidential elections of 2015. We define discussion topics from the tweet’s hashtags by constructing a weighted network, and we analyze the evolution of the alignment among different political groups of users during the period. Then we extract conclusions about how these political groups interact and change their behavior in different moments of the electoral period. 
Thursday 24 January 2019, 16:00 at LPT, 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  For more than eighty years, we face evidence that about $27\%$ of the energy budget of the universe today is in the form of a matter content which interacts gravitationally with the ordinary matter and do not emit or absorb light in a perceptible way  the dark matter (DM). If this matter is made out of particles, the standard model of particle physics (SM) must be extended. Well motivated SM extensions can accommodate DM candidates featuring sizable (detectable!) nongravitational couplings to SM particles. However, the null results of the numerous experiments looking for dark matter motivates candidates which evade current detection due to their very feeble couplings to SM particles. Feebly interacting massive particles (FIMPs) are DM candidates whose interactions are so feeble that their production in the early universe must be nonthermal. A theoretical difficulty in this case is accommodating such tiny couplings in a satisfactory way. In this talk, we show that if heavy fields ($10^{10}10^{16}~GeV$) mediate the DMSM interactions, DM candidates are inevitably FIMPs. Moreover, since the reheating scale in many scenarios lies in the range $10^{7}10^{10}~GeV$, the relic density of FIMPs in this case is likely to happen during the reheating period. Such heavy fields are actually needed in theoretically well motivated high energy scenarios like for instance GUT, seesaw, leptogenesis and inflation  we call this interesting coincidence the ``FIMP wonder". We explore different realizations of such possibility, with models involving moduli, fermions, gauge bosons and spin2 fields as heavy mediators. 
Friday 25 January 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 25 January 2019, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmechhepthmathph 



Abstract:  Bipartite entanglement entropy is a convenient observable to characterise critical and topological phases of matter. Despite numerous recent efforts, it remains a challenge to obtain both analytical results as well as experimental measurements of this quantity, even for simple systems. Some progress has been achieved recently by realising that in specific cases, e.g. for N noninteracting particles, the entanglement entropy is directly proportional to the number vari ance in the large N limit [1]. This number variance corresponds to the variance of the number of particles in a given domain, an observable much easier to measure experimentally. In this talk I will present a system of noninteracting fermions in two dimensions trapped by an harmonic potential and rotating at constant frequency. I will first show that the groundstate of this model can be mapped to the socalled complex Ginibre ensemble of Random Matrix Theory (RMT). Then I will use RMT techniques to obtain both the entanglement en tropy and the number variance for the fermions in a disk [2]. This computation remains valid for any number N of particles. In the large N limit, we show that the proportionality between number variance and entanglement entropy holds in the bulk, i.e. far enough from the edge of the density while it breaks down at this edge. References : [1] I. Klich, L. Levitov, Quantum noise as an entanglement meter, Phys. Rev. Lett. 102, 100502 (2009); [2] B. LacroixAChezToine, S. N. Majumdar and G. Schehr, Entanglement Entropy and Full Counting Statistics for 2dRotating Trapped Fermions, arXiv preprint 1809.05835, (2018). 
Tuesday 29 January 2019, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  A rather minimal possibility is that dark matter consists of the gauge bosons of a spontaneously broken symmetry. Here we explore the possibility of detecting the gravitational waves produced by the phase transition associated with such breaking. Concretely, we focus on the scenario based on an SU(2) group and argue that it is a case study for the sensitivity of future gravitational wave observatories to phase transitions associated with dark matter. This is because there are few parameters and those fixing the relic density also determine the effective potential establishing the strength of the phase transition. Particularly promising for LISA is the supercool dark matter regime, with DM masses above O(100) TeV, for which we find that the gravitational wave signal is notably strong. In our analysis, we include the effect of astrophysical foregrounds, which are often ignored in the context of phase transitions. (based on 1809.01198 ) 
Tuesday 29 January 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. 
Tuesday 29 January 2019, 15:00 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  This talk presents the progress made in my research via the introduction of effective field theories (EFTs) into postNewtonian (PN) Gravity. These have been put forward in the context of gravitational waves (GWs) from the compact binary inspiral. The setup and the strategy of a multistage EFT framework, which is deployed for the PN binary inspiral problem, is outlined. I then present in more detail the study of two effective theories at the intermediate scales of the problem. First, the EFT for a single rotating compact object is considered, from which I proceed to the EFT of a compact binary system, viewed as a composite particle with internal binding interactions. I conclude with the prospects of building on the field, and using further modern field theory insights and tools, to address the study of GWs, as well as to expand our fundamental understanding of QFTs and Gravity theories at all scales. 
Wednesday 30 January 2019, 11:00 at LPT, 114  LPTPHYSMATH (Séminaires de PhysiqueMathématique du LPTOrsay)  grqchepth 



Abstract:  This talk presents the progress made in my research via the introduction of effective field theories (EFTs) into postNewtonian (PN) Gravity. These have been put forward in the context of gravitational waves (GWs) from the compact binary inspiral. The setup and the strategy of a multistage EFT framework, which is deployed for the PN binary inspiral problem, is outlined. I then present in more detail the study of two effective theories at the intermediate scales of the problem. First, the EFT for a single rotating compact object is considered, from which I proceed to the EFT of a compact binary system, viewed as a composite particle with internal binding interactions. I conclude with the prospects of building on the field, and using further modern field theory insights and tools, to address the study of GWs, as well as to expand our fundamental understanding of QFTs and Gravity theories at all scales. 
Wednesday 30 January 2019, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  Mapping class groups of infinite type surfaces, also called "big" mapping class groups, arise naturally in several dynamical contexts, such as twodimensional dynamics, onedimensional complex dynamics, "Artinization" of Thompson groups, etc. In this talk, I will present recent objects and phenomena related to big mapping class groups. In particular, I will define two faithful actions of some big mapping class groups. The first is an action by isometries on a Gromovhyperbolic graph. The second is an action by homeomorphisms on a circle in which the vertices of the graph naturally embed. I will describe some properties of the objects involved, and give some fruitful relations between the dynamics of the two actions. For example, we will see that loxodromic elements (for the first action) necessarily have rational rotation number (for the second action). If time allows, I will explain how to use these simultaneous actions to construct nontrivial quasimorphisms on subgroups of big mapping class groups. This is joint work with Alden Walker. 
Wednesday 30 January 2019, 16:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  The study of Anosov representations deals with discrete subgroups of Lie groups that have a nice limit set, meaning that they share the dynamical properties of limit sets in hyperbolic geometry. However, the geometry of these limits sets is different: while limit sets in hyperbolic geometry have a fractal nature (e.g. noninteger Hausdorff dimension), some Anosov groups have a more regular limit set (e.g. C1 for Hitchin representations). My talk will focus on quasiFuchsian subgroups of SO(n,2), and show that the situation is intermediate: their limit sets are Lipschitz submanifolds, but not C1. I will discuss the two main steps of the proof. The first one classifies the possible Zariski closures of such groups. The second uses antide Sitter geometry in order to determine the limit cone of such a group with a C1 limit set. Based on joint work with Olivier Glorieux. 
Thursday 31 January 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 31 January 2019, 11:00 at CPHT, Salle Louis Michel  SEMCPHT (Séminaire du CPHT)  hepth 



Abstract:  This talk presents the progress made in my research via the introduction of effective field theories (EFTs) into postNewtonian (PN) Gravity. These have been put forward in the context of gravitational waves (GWs) from the compact binary inspiral. The setup and the strategy of a multistage EFT framework, which is deployed for the PN binary inspiral problem, is outlined. I then present in more detail the study of two effective theories at the intermediate scales of the problem. First, the EFT for a single rotating compact object is considered, from which I proceed to the EFT of a compact binary system, viewed as a composite particle with internal binding interactions. I conclude with the prospects of building on the field, and using further modern field theory insights and tools, to address the study of GWs, as well as to expand our fundamental understanding of QFTs and Gravity theories at all scales. 
Thursday 31 January 2019, 14:30 at IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 


Friday 1 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 1 February 2019, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmech 



Abstract:  Understanding the statistical properties of complex and/or random landscapes in highdimensional spaces is a central problem in a variety of different contexts, from glassy systems to computer science, ecology and biology. Among these properties, an important role is played by the statistics of the number of stationary points, which is expected to be relevant in determining the evolution of local dynamics within the landscape. In this talk, I will discuss the calculation of the typical number of local minima of the energy landscape of a simple model, which captures the competition between a deterministic ‘signal’ term and a noisy contribution. The model is obtained adding to the spherical pspin Hamiltonian a term favoring configurations that are aligned to a given configuration on the sphere (the signal), and reproduces the spikedtensor model for a specific choice of parameters. I will describe the phase transitions that occur in the structure of the landscape when changing the signaltonoise ratio, and provide some details on the calculation of the quenched complexity, that is performed using a replicated version of the KacRice formula. The talk is based on joint work with Gérard Ben Arous, Giulio Biroli and Chiara Cammarota. 
Friday 1 February 2019, 11:00 at APC, Amphitheatre Pierre Gilles de Gennes  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  the existence of black holes has been predicted for a long time, even before general relativity was sketched by Albert Einstein. Their extreme compactness makes them difficult to explore on spatial scales close to the event horizon. Sagittarius A*, at the center of the Galaxy, is the black hole with the largest angular size. A collaboration of European astronomers has built the GRAVITY instrument for the Very Large Telescope Interferometer of ESO to test the black hole nature of Sgr A* thanks to observations in the infrared at unprecedented spatial scales. General relativity can consequently also be tested at these scales in an extreme regime of gravity. I will present the results we have obtained with the star S2, the closest star known to Sgr A*. I will also present the first results on infrared flares occurring near the event horizon. I will conclude on the promising prospects of GRA 
Friday 1 February 2019, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  In March 2018 the EDGES experiment has reported the discovery of a 21cm signal in absorption between redshift 20 and 15. This measurement, if confirmed, is fundamental for astrophysics because it can give us information about the epoch of reionization soon after the formation of first stars and galaxies. This talk is organised in three parts. In the first part I will present the EDGES experiment and the procedure the collaboration has used to extract the broad absorption profile from strong foreground of galactic synchrotron emission. Then I will review the physics of the 21cm signal and the history of the InterGalactic Medium (IGM) properties assuming a LambdaCDM Universe. Finally, I will conclude with a simple application of this measurement to set bounds on the Dark Matter (DM) properties. In particular, annihilating DM particles produce significant heating of the IGM erasing the absorption feature measured by EDGES. These new limits on the annihilation cross section into standard model particles are comparable to the strongest ones from all other observables. 
Monday 4 February 2019, 14:00 at
IAP,
Henri Mineur ( Series of 4 lectures )  COURS (Cours)  grqc 


Tuesday 5 February 2019, 16:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  The astrophysical background of gravitational waves (AGWB) is made up by the incoherent superposition of gravitational wave signals emitted by a large number of resolved and unresolved astrophysical sources from the onset of stellar activity until today. I present a theoretical framework to fully characterize the AGWB in terms of energy density anisotropies which is based on the resolution of Olbers 
Thursday 7 February 2019, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 7 February 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Friday 8 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 8 February 2019, 11:00 at APC, Amphitheatre Pierre Gilles de Gennes  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  After the end of the O2 observing run, the LIGO and Virgo data were reprocessed and reanalyzed delivering the final O1 and O2 results. We will discuss the content of the catalog consisting of 10 BBH merger signals (4 of which are new discoveries) and one BNS merger signal (arXiv:1811.12907). We will also report the results of the companion article devoted to the astrophysical rates and parameters of the previously not known stellarmass BH population (arXiv:1811.12940). 

[ English version ] 