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 ] 
Monday 24 February 2020, 10:30 at
LPTMC,
Jussieu tower 1312 5th floor room 523 ( Minilecture: three times 1.5 hours + questions Lecture 1: "Kitaev's Toric Code and Surface Code" )  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  Building largescale quantum computers from imperfect components requires quantum error correction, for which the most promising approach builds on concepts from topological order. In this minicourse (3 lectures) we will introduce topological order on the example of Kitaev's toric code model, and show how this leads to quantum error correction in the socalled surface code and the socalled color code. We will deepen the concepts of topological order and of topological quantum computing, introducing simple examples of models with nonabelian anyons: an abstract model for Fibonacci anyons and topological superconductors with Majorana zero modes (Ising anyons). 
Monday 24 February 2020, 14:00 at LPTM, 4.13 St Martin II  SOUTENTH (Soutenance de thèse)  mathph 



Abstract:  Mean Field Games provide a powerful theoretical framework to deal with stochastic optimization problems involving a large number of coupled subsystems. They can find application in several fields, be it finance, economy, sociology, engineering ... However, this theory is rather recent and still poses many challenges. Its constitutive equations, for example, are difficult to analyse and the set of behaviours they highlight are illunderstood. While the large majority of contributions to this discipline come from mathematicians, economists or engineering scientists, physicist have only marginally be involved in it. In this thesis I try and start bridging the gap between Physics and Mean Field Games through the study of a specific class of models dubbed "quadratic". 
Tuesday 25 February 2020, 10:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  Hodge theory, as developed by Deligne and Griffiths, is the main tool for analyzing the geometry and arithmetic of complex algebraic varieties. It is an essential fact that at heart, Hodge theory is NOT algebraic. On the other hand, according to both the Hodge conjecture and the Grothendieck period conjecture, this transcendence is severely constrained. Tame geometry, whose idea was introduced by Grothendieck in the 80s, seems a natural setting for understanding these constraints. Tame geometry, developed by model theorists as ominimal geometry, has for prototype real semialgebraic geometry, but is much richer. It studies structures where every definable set has a finite geometric complexity. The aim of this course is to present a number of recent applications of tame geometry to several problems related to Hodge theory and periods. After recalling basics on ominimal structures and their tameness properties, I will discuss:  the use of tame geometry in proving algebraization results (PilaWilkie theorem; ominimal Chow and GAGA theorems in definable complex analytic geometry);  the tameness of period maps; algebraicity of images of period maps;  functional transcendence results: AxSchanuel conjecture from abelian varieties to Shimura varieties and variations of Hodge structures. Applications to atypical intersections (AndréOort conjecture and ZilberPink conjecture);  the geometry of Hodge loci and their closures. 
Tuesday 25 February 2020, 11:15 at IJCLAB, Building 210 room 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  Event generation for the LHC can be supplemented by generative adversarial networks, which generate physical events and avoid highly inefficient event unweighting. For top pair production we show how such a network describes intermediate onshell particles, phase space boundaries, and tails of distributions. In particular, we introduce the maximum mean discrepancy to resolve sharp local features. The generative network can be extended to perform addition and subtraction of event samples, a common problem in LHC simulations. We show how generative adversarial networks can produce new event samples with a phase space distribution corresponding to added or subtracted input samples. We illustrate its performance for the subtraction of the photon continuum from the complete Drell–Yan process. 
Tuesday 25 February 2020, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  The discovery of a Higgs boson in 2012 has been a milestone in particle physics and the start of a new era of collider physics where the exploration of a new type of particle is possible, which was not accessible before. The properties of this Higgs boson can serve as a window to new physics, and high experimental but also precise theoretical input is needed to open it. In this talk, after a short review of the status of the investigation of the discovered Higgs boson, I will discuss how the determination of its properties can shed light on physics beyond the Standard Model of particle physics and consider different approaches to possible new physics. I will comment on current and future improvements on the theory side needed to draw reliable conclusions from the experimental data. 
Wednesday 26 February 2020, 10:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  Hodge theory, as developed by Deligne and Griffiths, is the main tool for analyzing the geometry and arithmetic of complex algebraic varieties. It is an essential fact that at heart, Hodge theory is NOT algebraic. On the other hand, according to both the Hodge conjecture and the Grothendieck period conjecture, this transcendence is severely constrained. Tame geometry, whose idea was introduced by Grothendieck in the 80s, seems a natural setting for understanding these constraints. Tame geometry, developed by model theorists as ominimal geometry, has for prototype real semialgebraic geometry, but is much richer. It studies structures where every definable set has a finite geometric complexity. The aim of this course is to present a number of recent applications of tame geometry to several problems related to Hodge theory and periods. After recalling basics on ominimal structures and their tameness properties, I will discuss:  the use of tame geometry in proving algebraization results (PilaWilkie theorem; ominimal Chow and GAGA theorems in definable complex analytic geometry);  the tameness of period maps; algebraicity of images of period maps;  functional transcendence results: AxSchanuel conjecture from abelian varieties to Shimura varieties and variations of Hodge structures. Applications to atypical intersections (AndréOort conjecture and ZilberPink conjecture);  the geometry of Hodge loci and their closures. 
Wednesday 26 February 2020, 12:00 at LPENS, Conf. IV  FORUMENS (Forum de Physique Statistique @ ENS)  condmat.statmech 



Abstract:  Thermal soaring is a major natural instance of animal behavior in the presence of complex orientation cues. The problem is deeply rooted in physics and biology, with the prowess by birds constituting a challenge for artificial systems built for technological applications. I will first introduce the natural phenomenology, then review the physics that controls the complexity of the orientation cues, and finally show how machine learning methods are brought to bear on identifying effective flying strategies. Results are applied to gliders in the field, and provide insight into the decision processes and the sensorimotor cues utilized by birds. 
Wednesday 26 February 2020, 13:45 at LKB, Ecole Normale supérieure – 24, rue Lhomond – Conf IV – 75005 Paris  SEMLKB (Séminaire du Laboratoire Kastler Brossel)  quantph 



Abstract:  Ultrashort laser pulses grant access to an instantaneous and controlled creation of electrons and ions in a quantum gas. A single femtosecond laser pulse can ionize up to several thousand atoms, thus triggering the formation of strongly coupled ultracold plasmas. We report on the observation of ultrafast electron cooling in an expanding microplasma from 5000 K to about 1 K within less than one picosecond. Our experimental setup allows measuring the electronic kinetic energy distribution with meV resolution. Furthermore, we have performed numerical simulations of the plasma dynamics that are in excellent agreement with the measurements and provide insights into the thermalization mechanisms on subnanosecond timescales. 
Thursday 27 February 2020, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 27 February 2020, 11:15 at IJCLAB, Building 210 room 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  In this talk I will discuss collider searches for new physics with top quarks from two perspectives. Heavy new physics is best searched for through indirect effects in precision observables. Light and feebly coupled new physics can produce exotic signatures with longlived particles. I will present new ideas how to search effectively in both directions at the LHC and at Belle II. 
Thursday 27 February 2020, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  I will discuss worldvolume effective theories describing black holes and branes in higherdimensional gravity and supergravity. I will review how these can be used to perturbatively construct nontrivial black holes solutions with various topologies, geometries and with arbitrary asymptotics. Examples include asymptotically flat black helicoidal branes, rings and tori as well as asymptotically plane wave black Scherksurfaces. I will also briefly discuss extremal horizons and applications to antibrane metastable states in supergravity. Finally, I will show how this effective theory can be used to study instabilities of asymptotically flat black rings as well as (Anti)de Sitter black rings. 
Thursday 27 February 2020, 13:30 at
LPTMC,
Jussieu tower 1312 5th floor room 523 ( Minilecture: three times 1.5 hours + questions Lecture 2: "Fibonacci anyons, and theoretical topological quantum computing" )  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  Building largescale quantum computers from imperfect components requires quantum error correction, for which the most promising approach builds on concepts from topological order. In this minicourse (3 lectures) we will introduce topological order on the example of Kitaev's toric code model, and show how this leads to quantum error correction in the socalled surface code and the socalled color code. We will deepen the concepts of topological order and of topological quantum computing, introducing simple examples of models with nonabelian anyons: an abstract model for Fibonacci anyons and topological superconductors with Majorana zero modes (Ising anyons). 
Thursday 27 February 2020, 14:00 at LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  condmat 



Abstract:  We report the structural and electronic properties of the graphene/MoS 2 bilayer heterostructures, for theoretical study calculations we used Density functional theory [Abinit] with Van der Waals corrections. We analyze the interlayer spacing between the graphene and MoS 2 layers and also the charge transfer between the layers. In particular, we focus on the structural and electrical properties of bilayer heterostructures with different supercell geometries, with and without optimized bilayer heterostructures. These heterostructures are created with different supercell geometries like graphene (4x4)/MoS 2 (3x3) [4:3], graphene (5x5)/MoS2(4x4)[5:4] and graphene (9x9)/MoS2(7x7)[9:7] having different magnitudes of lattice mismatch. 
Friday 28 February 2020, 13:00 at DPTPHYSENS, Conf IV  BIOPHYENSESPCI (Séminaire de biophysique ENSESPCI)  physics.bioph 



Abstract:  The extensive heterogeneity of biological data poses challenges to analysis and interpretation. Construction of a largescale mechanistic model of Escherichia coli enabled us to integrate and crossevaluate a massive, heterogeneous dataset based on measurements reported by various labs over decades. We identified inconsistencies with functional consequences across the data, including: that the data describing total output of the ribosomes and RNA polymerases is not sufficient for a cell to reproduce measured doubling times; that measured metabolic parameters are neither fully compatible with each other nor with overall growth; that essential proteins are absent during the cell cycle  and the cell is robust to this absence. Finally, considering these data as a whole leads to successful predictions of new experimental outcomes, in this case protein halflives. 
Monday 2 March 2020, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  I will present a new method for studying UV complete unitary quantum field theories. The method relies on unitarity formulated as a semidefinite condition on a certain 3 by 3 matrix involving partial amplitudes, form factors and the spectral density. I will apply this method to integrable models in 2d. I will then discuss its applications to higher dimensions. 
Monday 2 March 2020, 11:30 at LPTENS, Scherk library (formerly LPTENS library)  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 


Monday 2 March 2020, 13:30 at LPENS, Conf IV  LPENSMDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS)  condmat 



Abstract:  According to quantum mechanics, an electromagnetic mode without real photon excitations is nontrivial. It gives rise to vacuum electric field fluctuations. Despite averaging to zero over time, these fluctuations are responsible for the spontaneous emission, the Lamb shift and the Casimir effect. Using Landau polaritons, we demonstrate experimentally that the vacuum electric field acts on electron transport. The DC magneto resistance of the cavityembedded 2D electron gas is changed due to the coupling to vacuum. Intriguingly, our experimental platform allows to tune the vacuum mode insitu, while observing the response in the resistance. 
Monday 2 March 2020, 14:00 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire Géométrie et Quantification )  MATHIHES (TBA)  math 



Abstract:  Whereas the exponential map from a Lie algebra to a Lie group can be viewed as the monodromy of a singular connection A dz/z on a disk, the wild character varieties are the receptacles for the monodromy data for arbitrary meromorphic connections on Riemann surfaces. This suggests one should think of the wild character varieties (or the full nonabelian Hodge triple of spaces, bringing in the meromorphic Higgs bundle moduli spaces too) as global analogues of Lie groups, and try to classify them. As a step in this direction I'll explain some recent joint work with D. Yamakawa that defines a diagram for any algebraic connection on a vector bundle on the affine line. This generalises the definition made by the speaker in the untwisted case in 2008 in arXiv:0806.1050 Apx. C, related to the « quiver modularity theorem », that a large class of Nakajima quiver varieties arise as moduli spaces of meromorphic connections on a trivial vector bundle the Riemann sphere, proved in the simplylaced case and conjectured in general in op.cit. (published in Pub. Math. IHES 2012), and proved in general by HiroeYamakawa (Adv. Math. 2014). In particular this construction of diagrams yields all the affine Dynkin diagrams of the Okamoto symmetries of the Painlevé equations, and recovers their special solutions upon removing one node. The case of Painlevé 3 caused the most difficulties. 
Monday 2 March 2020, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  Recent work of AlessandriniLeeSchaffhauser generalized the theory of higher Teichmüller spaces to the setting of orbifold surfaces. In particular, these authors proved that, as in the torsionfree surface case, there is a "Hitchin component" of representations into PGL(n,R) which is homeomorphic to a ball. They explicitly compute the dimension of Hitchin components for triangle groups, and find that this dimension is positive except for a finite number of lowdimensional examples where the representations are rigid. In contrast with these results and with the torsionfree surface group case, we show that the composition of the geometric representation of a hyperbolic triangle group with a diagonal embedding into PGL(2n,R) or PSp(2n,R) is always locally rigid. 
Monday 2 March 2020, 15:30 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire Géométrie et Quantification )  MATHIHES (TBA)  math 



Abstract:  A classical principle in deformation theory asserts that any formal deformation problem over a field of characteristic zero is classified by a differential graded Lie algebra. Using the Koszul duality between Lie algebras and commutative algebras, Lurie and Pridham have given a more precise description of this principle: they establish an equivalence of categories between dgLie algebras and formal moduli problems indexed by Artin commutative dgalgebras. I will describe a variant of this result for deformation problems around schemes over a field of characteristic zero. In this case, there is an equivalence between the homotopy categories of dgLie algebroids and formal moduli problems on a derived scheme. This can be viewed as a derived version of the relation between Lie algebroids and formal groupoids. 
Monday 2 March 2020, 16:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  We investigate properties of some spherical fonctions defined on hyperbolic groups using boundary representations on the Gromov boundary endowed with the PattersonSullivan measure class. We prove sharp decay estimates for spherical functions as well as spectral inequalities associated with boundary representations. This point of view on the boundary allows us to view the socalled property RD (Rapid Decay, also called Haagerup's inequality) as a particular case of a more general behavior of spherical functions on hyperbolic groups. Then I will explain how these representations are related to the socalled "complementary series". The problem of the unitarization of such representations will be at the heart of the discussion. If time permits, I will try to explain the idea of a constructive proof, using a boundary unitary representation, of a result due to de la Harpe and Jolissaint asserting that hyperbolic groups satisfy property RD. 
Tuesday 3 March 2020, 10:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  Hodge theory, as developed by Deligne and Griffiths, is the main tool for analyzing the geometry and arithmetic of complex algebraic varieties. It is an essential fact that at heart, Hodge theory is NOT algebraic. On the other hand, according to both the Hodge conjecture and the Grothendieck period conjecture, this transcendence is severely constrained. Tame geometry, whose idea was introduced by Grothendieck in the 80s, seems a natural setting for understanding these constraints. Tame geometry, developed by model theorists as ominimal geometry, has for prototype real semialgebraic geometry, but is much richer. It studies structures where every definable set has a finite geometric complexity. The aim of this course is to present a number of recent applications of tame geometry to several problems related to Hodge theory and periods. After recalling basics on ominimal structures and their tameness properties, I will discuss:  the use of tame geometry in proving algebraization results (PilaWilkie theorem; ominimal Chow and GAGA theorems in definable complex analytic geometry);  the tameness of period maps; algebraicity of images of period maps;  functional transcendence results: AxSchanuel conjecture from abelian varieties to Shimura varieties and variations of Hodge structures. Applications to atypical intersections (AndréOort conjecture and ZilberPink conjecture);  the geometry of Hodge loci and their closures. 
Tuesday 3 March 2020, 11:00 at CPHT, Salle Louis Michel  SEMCPHT (Séminaire du CPHT)  hepth 



Abstract:  TBA 
Tuesday 3 March 2020, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  In cosmological scenarios beyond thermal freezeout dark matter interactions with standardmodel particles can be tiny. This leads to mediators with a lifetime that is long compared with the scales of particle colliders. In this talk I will discuss two new ideas for collider searches with longlived mediators: soft displaced objects as signs of compressed dark sectors at the LHC; and displaced vertices from long lived light scalars at Belle II. I will show that novel search strategies allow us to explore dark matter interactions ranging over several orders of magnitude. 
Tuesday 3 March 2020, 14:00 at LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  mathph 



Abstract:  Even though the Heisenberg spin chain is one of the best studied examples of quantum integrable systems the crucial problem of analytic description of equilibrium and outof equilibrium dynamics remains mostly unsolved for this fundamental model. In particular, there exist very few analytic results for timedependent correlation functions even for the equilibrium case. The main obstacle is the lack of manageable analytic representations for the relevant form factors and overlaps. In this talk I’ll discuss the new method we developed to compute explicitly the form factors for lowenergy excited states of the XXX chain. I will show how to use this technique for simplest excitations and how to take into account bound states corresponding to the complex roots of the Bethe equations. 
Tuesday 3 March 2020, 17:15 at DPTPHYSENS, Conf IV (E244)  Département de Physique de l'ENS 24 rue Lhomond 75005 PARIS  COLLOQUIUMENS (Colloquium of the Physics Department of ENS)  physics 



Abstract:  Gravitational astronomy, which began on September 14th, 2015 with the LIGO detection of the merger of two black holes, has demonnstrated all its scientific potential during the 01 (LIGO) and 02 (LIGOVirgo) observation periods, between 2015 and 2017. At present, LIGO and Virgo are carrying out a third observation run, started on April 1st 2019, with the detection of a few gravitationalwave candidates per month. A program of detector upgrades, alternated with observation runs, will continue for most of the 2020 decade. After that period, a radical change of the detector infrastructure is necessary. The Einstein Telescope Europan project aims to continue the scientific program of Virgo and LIGO, with a detector having tenfold greater sensitivity than current instruments, 10 km arms, and an underground infrastructure. In this presentation, I will begin by introducing the scientific motivations for Einstein Telescope, then I will describe the planned technology and the implementation plans for the detector. 
Wednesday 4 March 2020, 10:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  Hodge theory, as developed by Deligne and Griffiths, is the main tool for analyzing the geometry and arithmetic of complex algebraic varieties. It is an essential fact that at heart, Hodge theory is NOT algebraic. On the other hand, according to both the Hodge conjecture and the Grothendieck period conjecture, this transcendence is severely constrained. Tame geometry, whose idea was introduced by Grothendieck in the 80s, seems a natural setting for understanding these constraints. Tame geometry, developed by model theorists as ominimal geometry, has for prototype real semialgebraic geometry, but is much richer. It studies structures where every definable set has a finite geometric complexity. The aim of this course is to present a number of recent applications of tame geometry to several problems related to Hodge theory and periods. After recalling basics on ominimal structures and their tameness properties, I will discuss:  the use of tame geometry in proving algebraization results (PilaWilkie theorem; ominimal Chow and GAGA theorems in definable complex analytic geometry);  the tameness of period maps; algebraicity of images of period maps;  functional transcendence results: AxSchanuel conjecture from abelian varieties to Shimura varieties and variations of Hodge structures. Applications to atypical intersections (AndréOort conjecture and ZilberPink conjecture);  the geometry of Hodge loci and their closures. 
Wednesday 4 March 2020, 13:30 at
LPTMC,
Jussieu tower 1312 5th floor room 523 ( Minilecture: three times 1.5 hours + questions Lecture 3: "Majorana Zero Modes and practical topological quantum computing" )  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  Building largescale quantum computers from imperfect components requires quantum error correction, for which the most promising approach builds on concepts from topological order. In this minicourse (3 lectures) we will introduce topological order on the example of Kitaev's toric code model, and show how this leads to quantum error correction in the socalled surface code and the socalled color code. We will deepen the concepts of topological order and of topological quantum computing, introducing simple examples of models with nonabelian anyons: an abstract model for Fibonacci anyons and topological superconductors with Majorana zero modes (Ising anyons). 
Wednesday 4 March 2020, 13:45 at LKB, Ecole Normale supérieure – 24, rue Lhomond – Conf IV – 75005 Paris  SEMLKB (Séminaire du Laboratoire Kastler Brossel)  quantph 



Abstract:  Gravitational Quantum States (GQS) and WhisperingGallery Quantum (WGS) states of light neutral particles are a useful tool for highprecision measurements. Such quantum states of neutrons have been observed [1] and used ourdays by several research groups to constrain fundamental shortrange interactions. Analogous states of ultracold atoms and antiatoms have been predicted [2]; they appear due to quantum reflection of ultracold (anti)atoms from surface [3]. Studies with hydrogen is the goal of a new GRASIAN collaboration. Those with antihydrogen can be pursuit in the future by GBAR collaboration at CERN in more precise experiments, which test the equivalence principle with antimatter [4]. In all these cases, a long observation time thus a much better energy resolution and precision can be achieved in a novel Magneto Gravitational Trap (MGT), where the particles will be trapped vertically by gravity and a mirror, and horizontally by a magnetic field [5]. The ultralow energies of (anti)atoms and long lifetimes of GQS provide unique conditions for precision gravitational, optical and hyperfine spectroscopy of (anti)atoms. In this talk we will discuss some experimental and theoretical results as well as prospects of these activities 
Wednesday 4 March 2020, 14:00 at LPENS, L369  LPENSACE (Astronomy and Cosmology at ENS)  astroph 



Abstract:  I will discuss an approach to search for axion dark matter with an especially desigend superconducting radio frequency cavity. Our approach exploits axioninduced transitions between nearly degenerate resonant modes of frequency close to a GHz. Compared to traditional detection strategies this allows for parametrically enhanced signal power for axions lighter than a GHz (~microeV). The projected sensitivity covers unexplored parameter space for QCD axion dark matter for axion masses between a GHz and 10 MHz. It is also sensitive to about eight orders of magnitude in axionlike dark matter coupling to photons for axion masses between GHz and Hz. 

[ English version ] 