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  
[ scheduler view ] 
Thursday 22 April 2021, 11:00 at
IHP,
Zoom ( https://zoom.us/j/97507124810 Password: 1234 )  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  There are no particles in conformal field theory, but it is still possible to define scattering amplitudes using a conformal version of the LSZ reduction formalism, which makes use of branch points instead of poles in correlation functions expressed in momentum space. These amplitudes have many familiar properties, including crossing symmetry and unitarity cuts. They match ordinary scattering amplitudes in perturbative examples, but are truly nonperturbative and can potentially be used as a new approach to bootstrap a theory. 
Monday 26 April 2021, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  We discuss the construction of logarithmic representation of Virasoro algebra at generic central charge by using derivative of fields with respect to their conformal dimensions. The resulting representations come with a free parameter $\kappa$ which can be fixed based on the existence of degenerate fields. As an application, we describe the logarithmic structure in the critical $Q$state Potts model at generic central charge. We validate our description by numerically bootstrapping the fourpoint connectivities in the Potts model. Our results hold for generic values of $Q$ on the complex plane. 
Monday 26 April 2021, 11:00 at IAP, Webinar for zoom details contact fumagall@iap.fr  SEMGRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP)  astroph 



Abstract:  The recent detections of gravitational waves (GWs) from binary black holes (BBHs) from LIGOVirgo and the latest data releases allow to open different major windows on our understanding of the universe, among which GWbased measurements of cosmological parameters, new tests of General Relativity (GR) at cosmological scales, and BBHs population studies. In this talk I will present some results in these directions based on the GWTC2 catalogue and discuss the interplay among them. In particular, cosmological tests are based on the fact that the luminosity distance is measured directly from the GW signal. By adding independent information on the redshift we can thus test the distanceredshift relation. Moreover, this is modified in presence of new physics at cosmological scales, providing a possibility to test GR. I will discuss in particular two ways of obtaining the redshift information for ``dark sirens'' (i.e., compact binary coalescences without an electromagnetic counterpart), namely using galaxy catalogues or information from the BBH mass distribution and rate evolution. Besides showing results for the measurement of the Hubble constant and the parameters that govern deviations from GR, I will be focussing on methodological aspects and relevant sources of systematics. I will finally discuss the fact that the two methods are tightly related, so population studies and cosmology have to proceed together. This is particularly relevant for modifications of gravity. All the python code written to produce the joint population and cosmological analysis, as well as correlation with galaxy catalogues, is (or will shortly be) publicly available. 
Tuesday 27 April 2021, 16:00 at IHP, Seminar via zoom https://ijclab.zoom.us/j/94900481972  P^3 (Particle Physics in Paris)  hepphhepth 



Abstract:  Recent data in semileptonic Bmeson decays indicate a coherent pattern of deviations from the Standard Model. I critically review these data and discuss their interpretation, both in terms of a generic effectivetheory approach and in terms of more complete, but also more speculative, extensions of the Standard Model. Implications for future measurements are also briefly discussed 
Tuesday 27 April 2021, 17:00 at
IHES,
zoom ( Zoom Réunion : https://us02web.zoom.us/j/81778962715?pwd=QnpNS2ErSnBCTWRYUHphd1VMMysyZz09 ID de réunion : 817 7896 2715 Code secret : 800452 )  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  Recently methods of quantum statistical mechanics have been fruitfully applied to the study of phases of quantum lattice systems at zero temperature. For example, a rigorous definition of a ShortRange Entangled phase of matter has been given and a classification of such phases in one spatial dimension has been achieved. I will discuss some of these developments, focusing on the topology and geometry of the space of ShortRange Entangled states. According to a conjecture of A. Kitaev, these spaces form a loop spectrum in the sense of homotopy theory. This conjecture implies that to any family of ShortRange entangled states in one dimension one can associate a gerbe on the parameter space. I will show how to construct such a gerbe. Thе curvature of this gerbe is a closed 3form with quantized periods and can be regarded as a higherdimensional generalization of the curvature of the Berry connection. 
Friday 30 April 2021, 14:00 at DPTPHYSENS, GoToMeeting  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  Positivity bounds are powerful tools to constrain effective field theories. Utilizing the partial wave expansion in the dispersion relation and the full crossing symmetry of the scattering amplitude, we derive several sets of generically nonlinear positivity bounds for a generic scalar effective field theory: We refer to these as the PQ, Dsu, Dstu and D¯stu bounds. While the PQ bounds and Dsu bounds only make use of the s↔u dispersion relation, the Dstu and D¯stu bounds are obtained by further imposing the s↔t crossing symmetry. In contradistinction to the linear positivity for scalars, these inequalities can be applied to put upper and lower bounds on Wilson coefficients, and are much more constraining as shown in the lowest orders. In particular we are able to exclude theories with soft amplitude behaviour such as weakly broken Galileon theories from admitting a standard UV completion. We also apply these bounds to chiral perturbation theory and we find these bounds are stronger than the previous bounds in constraining its Wilson coefficients. (based on 2011.02400 ) 
Monday 3 May 2021, 11:00 at IAP, Webinar for zoom details contact fumagall@iap.fr  SEMGRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP)  astroph 


Tuesday 4 May 2021, 10:30 at
LPTMC,
online, INSP ( https://zoom.us/j/3630156422?pwd=anVyV3BkUXQ5RDVwaGg2SFk0NzlnZz09 )  COURS (Cours)  condmat.meshall 



Abstract:  This set of three lectures is essentially a basic introduction to quantum computing from a physicist point of view. For each theoretical concept, I will try to analyse what it would take for an actual hardware to work in practice and identify probable bottlenecks. The talks should be accessible to anyone with a working knowledge of quantum mechanics. The lectures will be organised around a few questions: Lecture 1) What's a quantum computer? How can a quantum computer be exponentially faster than a classical one? What would it take to get this to work? Lecture 2) How could one get rid of the ubiquitous and infamous decoherence with "quantum error correction"? Is this feasible? Lecture 3) Where are we now? Have we really reached quantum supremacy? And what does supremacy mean by the way? 
Thursday 6 May 2021, 14:00 at LPTM, Distanciel TEAMS  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  mathph 



Abstract:  Defining the chaotic properties of quantum systems is a notoriously difficult problem, because of the fundamental fact that in quantum mechanics trajectories are not welldefined. A historically very productive direction has been the investigation of spectral properties of quantum Hamiltonian in a statistical way: it emerges that chaos is associated with strong repulsion between energy levels. When one tries to apply this recipe to manybody systems, it is clear that a hierarchy of energy/time scales can emerge due to the interplay of farther components of the system which are less and less correlated. Recently, the use of quantum circuits composed by random gates has allowed explicit calculations clarifying to what extent chaos emerges for spatially extended systems. In this talk, I will review some recent advances in the field with an emphasis on the strong success of a "Wick rotation" which exchanges space and time. Thanks to this formulation, we have been able to connect spectral properties to a spectrum of Lyapunov exponents, which emerge from the infinite product of random operators in the space direction. 
Monday 10 May 2021, 11:00 at IAP, Webinar for zoom details contact fumagall@iap.fr  SEMGRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP)  astroph 


Tuesday 11 May 2021, 10:30 at
LPTMC,
online, INSP ( https://zoom.us/j/3630156422?pwd=anVyV3BkUXQ5RDVwaGg2SFk0NzlnZz09 )  COURS (Cours)  condmat.meshall 



Abstract:  This set of three lectures is essentially a basic introduction to quantum computing from a physicist point of view. For each theoretical concept, I will try to analyse what it would take for an actual hardware to work in practice and identify probable bottlenecks. The talks should be accessible to anyone with a working knowledge of quantum mechanics. The lectures will be organised around a few questions: Lecture 1) What's a quantum computer? How can a quantum computer be exponentially faster than a classical one? What would it take to get this to work? Lecture 2) How could one get rid of the ubiquitous and infamous decoherence with "quantum error correction"? Is this feasible? Lecture 3) Where are we now? Have we really reached quantum supremacy? And what does supremacy mean by the way? 
Tuesday 11 May 2021, 14:00 at
LPTENS,
GoToMeeting ( https://www.gotomeet.me/LPENSIF Code: 418109349 )  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 


Tuesday 18 May 2021, 10:30 at
LPTMC,
online, INSP ( https://zoom.us/j/3630156422?pwd=anVyV3BkUXQ5RDVwaGg2SFk0NzlnZz09 )  COURS (Cours)  condmat.meshall 



Abstract:  This set of three lectures is essentially a basic introduction to quantum computing from a physicist point of view. For each theoretical concept, I will try to analyse what it would take for an actual hardware to work in practice and identify probable bottlenecks. The talks should be accessible to anyone with a working knowledge of quantum mechanics. The lectures will be organised around a few questions: Lecture 1) What's a quantum computer? How can a quantum computer be exponentially faster than a classical one? What would it take to get this to work? Lecture 2) How could one get rid of the ubiquitous and infamous decoherence with "quantum error correction"? Is this feasible? Lecture 3) Where are we now? Have we really reached quantum supremacy? And what does supremacy mean by the way? 
Monday 31 May 2021, 11:00 at IAP, Webinar for zoom details contact fumagall@iap.fr  SEMGRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP)  astroph 


Tuesday 8 June 2021, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTSEM (Séminaire du IPHT)  physics 



Abstract:  Sera annoncÃ© ultÃ©rieurement. 

[ English version ] 