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Friday 30 November 2018, 11:00 at APC, 454A  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  The second Gaia data release (DR2) has been published on 25 April 2018. It contains the parallaxes and proper motions of 1.3 billion sources (versus 2 millions in DR1) as well as the positions and Gmagnitudes of 400 millions additional sources. DR2 also contains new products, including Bp/Rpmagnitudes of 1.4 billion sources, 7.2 millions lineofsight velocities, stellar parameters for several tens millions stars, the detection of half a million variable stars and 14000 asteroids. In this seminar, I will detail the contents and performances of the release, discuss the usage of the data and I will present some of the first scientific results. 
Monday 3 December 2018, 10:45 at
LPTMC,
Jussieu, tower 1312, room 523 ( Phys. Rev. Lett. 118, 216801 )  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  We study the relation between the global topology of the Hofstadter butterfly of a multiband insulator and the topological invariants of the underlying Hamiltonian. The global topology of the butterfly, i.e., the displacement of the energy gaps as the magnetic field is varied by one flux quantum, is determined by the spectral flow of energy eigenstates crossing gaps as the field is tuned. We find that for each gap this spectral flow is equal to the topological invariant of the gap, i.e., the net number of edge modes traversing the gap. For periodically driven systems, our results apply to the spectrum of quasienergies. In this case, the spectral flow of the sum of all the quasienergies gives directly the RudnerLindnerBergLevin invariant that characterizes the topological phases of a periodically driven system. 
Tuesday 4 December 2018, 11:00 at CPHT, Louis Michel  COURS (Cours)  hepth 



Abstract:  Chaos is a wellunderstood phenomenon within classical physics. According to its simplest definition, it stems from the dynamics of particles, which follow trajectories with extreme sensitivity to initial conditions. Two commonly associated phenomena are the exponential Lyapunov divergence of initially nearby trajectories and the butterfly effect. In manybody quantum physics, the situation is completely different. There, the very definition of what quantum chaos is remains unclear. Even more elusive are its characterisation and classification. In this fourhour lecture course, I will discuss exciting recent revival of interest in addressing these questions, which was largely ignited by studies of the physics of black holes.  
Attachments: 
Tuesday 4 December 2018, 11:00 at LPTMS, IPNbatiment 100, Auditoriurm  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  physics 



Abstract:  TBA 
Tuesday 4 December 2018, 14:00 at CPHT, Louis Michel  COURS (Cours)  hepth 



Abstract:  Chaos is a wellunderstood phenomenon within classical physics. According to its simplest definition, it stems from the dynamics of particles, which follow trajectories with extreme sensitivity to initial conditions. Two commonly associated phenomena are the exponential Lyapunov divergence of initially nearby trajectories and the butterfly effect. In manybody quantum physics, the situation is completely different. There, the very definition of what quantum chaos is remains unclear. Even more elusive are its characterisation and classification. In this fourhour lecture course, I will discuss exciting recent revival of interest in addressing these questions, which was largely ignited by studies of the physics of black holes.  
Attachments: 
Tuesday 4 December 2018, 14:00 at APC, 646 A  Mondrian  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  Black holes appear to lead to information loss, thus violating one of the fundamental tenets of Quantum Mechanics. Recent InformationTheorybased arguments imply that information loss can only be avoided if at the scale of the black hole horizon there exists a structure (commonly called fuzzball or firewall) that allows information to escape. I will discuss the highlyunusual properties that this structure must have and how these properties emerge in the realization of this structure in String Theory via branes, fluxes and topology. I will then describe the implication of this structure for AdS_2 holography. 
Tuesday 4 December 2018, 16:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  After a brief review of some of the empirical correlations between dark and baryonic sectors within galaxies, I will discuss a theory of dark matter superfluidity as a potential explanation of this observations. I will argue that, depending on the mass and selfinteraction cross section of dark matter particles, the superfluid may in principle be formed in the central regions of galactic halos. After this, I will discuss the criteria that need to be met by superfluid properties in order to account for the abovementioned empirical correlations. 
Wednesday 5 December 2018, 09:00 at IPHT, Amphi Claude Bloch, Bât. 774  WORKCONF (Workshop or Conference)  physics 



Abstract:  Pioneering work in the field of conformal invariance and harmonic analysis on the conformal group was done more than 40 years ago. The field underwent a renewal with the advent of the conformal bootstrap program. The conference will bring together different generations of mathematical physicists to share their vision and their insights. \\ \\ (https://indico.in2p3.fr/event/17934/overview) 
Wednesday 5 December 2018, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Thursday 6 December 2018, 14:00 at APC, 454A  SEMEXCEP (Séminaire exceptionel)  astroph 



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


Monday 10 December 2018, 10:45 at LPTMC, LPTMC Jussieu tower 1312 room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Monday 10 December 2018, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  We present a framework for organising the correlations of interacting electrons, which provides access to a novel regime of strongly correlated behaviour. Following an introduction, we highlight two ways to characterise the electronic degree of freedom, either by the canonical fermion algebra or by the graded Lie algebra su(22). The first underlies Landau's Fermi liquid description of correlated matter, and we identify an alternative Fermi liquid regime governed by the latter. We exploit the su(22) algebra to derive a systematic expansion of the electronic correlations, and describe the resulting leading approximations to electronic spectral function. These reveal a splitting in two of the electronic band, a violation of the Luttinger sum rule, and a Mott metalinsulator transition. We conclude with a reinterpretation of the meaning of the term ``strongly correlated'', and offer a scheme which encompasses magnetic, electronic, and local moment systems. 
Tuesday 11 December 2018, 11:00 at CPHT, Louis Michel  COURS (Cours)  hepth 



Abstract:  Chaos is a wellunderstood phenomenon within classical physics. According to its simplest definition, it stems from the dynamics of particles, which follow trajectories with extreme sensitivity to initial conditions. Two commonly associated phenomena are the exponential Lyapunov divergence of initially nearby trajectories and the butterfly effect. In manybody quantum physics, the situation is completely different. There, the very definition of what quantum chaos is remains unclear. Even more elusive are its characterisation and classification. In this fourhour lecture course, I will discuss exciting recent revival of interest in addressing these questions, which was largely ignited by studies of the physics of black holes.  
Attachments: 
Tuesday 11 December 2018, 11:00 at LPTMS, LPTMS, salle 201, 2ème étage, Bât 100, Campus d'Orsay  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  physics 



Abstract:  Stabilizing and manipulating exotic emergent quasiparticles is one of the main goal of modern condensed matter physics. The quest for observing Majorana fermions and their nonAbelian braiding statistics in superconducting nanostructures is currently attracting a lot of attention, with fascinating prospects in faulttolerant quantum computation. Parafermions are the simplest generalization of Majorana fermions: they show nonAbelian fractional statistics and are typically associated with topological phases. We will discuss the possibility of harboring these exotic excitations in genuinely onedimensional electronic platforms. We focus on a specific model of fermions in one dimension with a generalized ZN multiplet pairing extending the standard and socalled Kitaev chain model. Using a combination of analytical techniques, we find an interesting topological phase intertwined with spontaneous symmetry breaking. Each symmetrybreaking sector is shown to possess a pair of boundary Majorana fermions encoding a topological character. A careful study of the quantum anomaly through pumping in the system finally reveals that parafermions exist in one dimension but only as nonlocal operators. References: Fernando Iemini, Christophe Mora & Leonardo Mazza, Topological phases of parafermions: a model with exactlysolvable ground states, Phys. Rev. Lett. 118, 170402 (2017) Leonardo Mazza, Fernando Iemini, Marcello Dalmonte & Christophe Mora, Poor man’s parafermions in a lattice model with even multiplet pairing, preprint condmat arXiv:1801.08548. 
Tuesday 11 December 2018, 14:00 at CPHT, Louis Michel  COURS (Cours)  hepth 



Abstract:  Chaos is a wellunderstood phenomenon within classical physics. According to its simplest definition, it stems from the dynamics of particles, which follow trajectories with extreme sensitivity to initial conditions. Two commonly associated phenomena are the exponential Lyapunov divergence of initially nearby trajectories and the butterfly effect. In manybody quantum physics, the situation is completely different. There, the very definition of what quantum chaos is remains unclear. Even more elusive are its characterisation and classification. In this fourhour lecture course, I will discuss exciting recent revival of interest in addressing these questions, which was largely ignited by studies of the physics of black holes.  
Attachments: 
Tuesday 11 December 2018, 14:00 at APC, 646 A  Mondrian  APCTH (Seminar of the theory group of APC)  hepth 


Tuesday 11 December 2018, 16:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  In this talk I will outline work I have done over the past 12 months or so on nonlinearly realised symmetries in effective field theories both on Lorentz invariant and Lorentz violating backgrounds. I will first discuss the general formulism of the coset construction and inverse Higgs constraints as a tool to construct nonlinear realisations of spontaneously broken symmetries. I will then explain how this provides a useful classification of scalar quantum field theories in flat space followed by discussing how it provides a useful tool for building inflationary models. I will also present a general classification of nonlinearly realised symmetries within the effective field theory framework of single clock cosmologies. I will make the talk very pedagogical. 
Thursday 13 December 2018, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 



Abstract:  (based on 1607.08467 ) 
Thursday 13 December 2018, 14:00 at CPHT, Salle de Conference Louis Michel (Bât.6 CPHT)  SEMCPHT (Séminaire du CPHT)  hepth 


Friday 14 December 2018, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmechhepthmathph 



Abstract:  In this talk I revisit Stokes drift in shallow water from a geometric perspective inspired by conformal field theory. Given a fluid on a circular pool supporting periodic waves, I argue that the displacement of fluid particles after one period involves a Berry phase associated with adiabatic conformal transformations. In particular, the phase shift produced by cnoidal waves can be evaluated in closed form, and matches the results of previous numerical estimates. Conceptually, this relates fluid dynamics, symplectic geometry, conformal field theory and Thomas precession. 
Friday 14 December 2018, 14:00 at APC, Amphitheatre Pierre Gilles de Gennes  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  TBA 
Monday 17 December 2018, 10:45 at LPTMC, Jussieu, tower 1312, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Tuesday 18 December 2018, 14:00 at APC, 646 A  Mondrian  APCTH (Seminar of the theory group of APC)  hepth 


Wednesday 19 December 2018, 11:00 at LPTMC, Jussieu, tower 1312, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Wednesday 19 December 2018, 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: 
Friday 21 December 2018, 10:30 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 


Friday 21 December 2018, 13:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTSEM (Séminaire du IPHT)  physics 


Tuesday 15 January 2019, 14:00 at APC, 646 A  Mondrian  APCTH (Seminar of the theory group of APC)  hepth 


Wednesday 16 January 2019, 11:30 at
IPN,
Bâtiment 100, Salle A015 ( $ $ )  IPNTHEO (Séminaire du groupe de physique théorique de l'IPN Orsay)  nuclth 



Abstract:  An exotic type of decay  cluster emission  was observed in actinides region in 1980's [1, 2, 3]. In this process a light nucleus, but heavier then alpha particle is emitted, while the heavy mass residue is close to doubly magic lead in all observed cases. Microscopic description of this phenomenon treated as a very asymmetric fission has been successfully performed within HFB model with Gogny interactions D1S [4]. The fission valley on the potential energy surface has been found and fission fragments have been identified as cluster radioactivity products. Recently the characteristic very asymmetric fission valleys have been also found in some superheavy nuclei. It has been shown that cluster radioactivity plays a nonnegligible role in this part of nuclear chart [5].\newline [1] H. J. Rose and G. A. Jones, Nature (London) 307, 245 (1984).\newline [2] A. Sandulescu, D. N. Poenaru, and W. Greiner, Sov. J. Part. Nucl. 11, 528 (1980).\newline [3] R. Bonetti and A. Guglielmetti, in Heavy Elements and Related Phe nomena, Vol. II, edited by W. Greiner and R. K. Gupta (World Scientific, Singapore, 1999), p. 643.\newline [4] M. Warda, J.M. Robledo, Phys. Rev. C 84, 044608 (2011).\newline [5] M. Warda, A. Zdeb, L.M. Robledo, arXiv:1807.00342  
Attachments: 

[ English version ] 