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 ] 
Friday 20 October 2017, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  JOURCLUB (Journal Club)  physics 



Abstract:  \noindent ``Integrability meeting ENS/IPhT'' \\ \\ We consider a problem of Bethe vectors scalar products of the models solvable by the (nested) algebraic Bethe ansatz. For the models with gl(2) symmetry or its qdeformation, the scalar products can be calculated straightforwardly via the standard arguments of the algebraic Bethe ansatz. However, for the models with higher rank symmetry, the technical complexity of such a calculation increases immensely. We suggest a new method based on the coproduct properties of the Bethe vectors. We illustrate this method by the example of the scalar products in the gl(2) based models. \\ \\ (IPhT organizer: Ivan Kostov) 
Friday 20 October 2017, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  JOURCLUB (Journal Club)  physics 



Abstract:  \noindent ``Integrability meeting ENS/IPhT'' \\ \\ (Based on arXiv:1610.08032) \\ We present a new way to construct eigenstates of integrable XXX quantum spin chains with SU(N) symmetry which bypasses the nesting procedure. The states are built by repeatedly acting on the vacuum with a single operator Bgood(u) evaluated at the Bethe roots. Our proposal serves as a compact alternative to the usual nested algebraic Bethe ansatz. Furthermore, the roots of this operator give the separated variables of the model, explicitly generalizing Sklyanin's approach to the SU (N) case. We present many tests of the conjecture and prove it in several special cases. We focus on rational spin chains with fundamental representation at each site, but expect that our main results are valid more generally. \\ \\ (IPhT organizer: Ivan Kostov) 
Tuesday 24 October 2017, 11:30 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  Studying strongly coupled CFTs with some global symmetry in sectors where the associated global charge is large, often leads to an effective action which is weakly coupled. In this regime, the computation of anomalous dimensions and fusion coefficients becomes perturbatively meaningful. I review our recent progress [arXiv:1610.04495, 1612.08985, 1707.00710] in understanding the largecharge sectors of classes of scalar CFTs in three dimensions, both at the level of the linear as well as nonlinear sigma model. Additionally, I comment on the verification of the analytic prediction via lattice simulations. 
Tuesday 24 October 2017, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 


Tuesday 24 October 2017, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  Abstract: Dark Matter which interacts strongly with itself, but only feebly with the Standard Model is a possibility that has been entertained to solve apparent smallscale structure problems that are pertinent to the noninteracting cold Dark Matter paradigm. We study the simple case in which the selfscattering rate today is regulated by kinematics and/or the abundance ratio, through the masssplitting of nearly degenerate pseudoDirac fermions or real scalars. We calculate the relic density of these states in a scenario where self scattering proceeds through offdiagonal couplings with a vector particle V (Dark Photon) and where the abundance is set through numberdepleting 4to2 reactions in the hidden sector, or, alternatively, via freezein. We study the implications of the considered models and their prospect of solving astrophysical smallscale structure problems. We also show how the introduction of the (meta)stable heavier state may be probed in future dark matter searches. 
Wednesday 25 October 2017, 14:00 at
LPTHE,
Bibliothèque du LPTHE ( PhD seminar )  SEMINFOR (Séminaire informel)  mathph 



Abstract:  TBA 
Wednesday 25 October 2017, 14:00 at LKB, Collège de France, salle 2  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  quantph 



Abstract:  The so called "fluctuation theorems" are one of the most important results in non equilibrium thermodynamics obtained during the last decades. They connect the behavior of a system evolving far away from equilibrium with certain properties of thermal equilibrium states of the same system. The work probability distribution plays a major role in such theorems and its measurement attracted a lot of interest recently. In this talk I will review a new strategy for measuring work on a quantum system which evolves out of equilibrium. I will also show how these ideas have been recently implemented in an experiment which enabled us to directly sample the work probability distribution. The "quantum work meter" I will present, built with an ensemble of cold Rubidium atoms manipulated by an atom chip, enabled us to perform a direct test of the most notable fluctuation theorem: the Jarzynski identity. 
Thursday 26 October 2017, 11:00 at IPN, Salle A015  IPNX (Séminaire commun de physique théorique des particules IPNCPHTX)  hepph 



Abstract:  Understanding the angular momentum decomposition and helicity sum rule for nucleons is of great interest in hadron physics. I will prove the Lorentz invariance of the angular momentum conservation law in the lightfront formulation. I will show explicitly that the zcomponent of the angular momentum for any relativistic system remains unchanged under Lorentz transformations generated by the lightfront kinematical boost operators. Applying the Lorentz invariance of angular momentum in the front form, I will present a selection rule for the orbital angular momentum which can be used to eliminate certain interaction vertices in QED and QCD. The selection rule can be generalized to any renormalizable theory to give an upper bound on the change of orbital angular momentum in scattering processes at any fixed order in perturbation theory. 
Tuesday 31 October 2017, 11:30 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  Quantum magnets in 2 spatial dimensions are effectively described by a 2+1D abelianhiggs theory with monopoles. Such materials support a phase of highly entangled ground state called the Valence Bond Solid phase, where spin1/2 excitations are confined into spin1 object. Moreover the ground state breaks lattice symmetries spontaneously and is therefore degenerate. The effective description has a striking resemblance to a version of QCD with adjoint matter, including the N=1 and N=2 Super YangMills theory as well as theta=pi pure YangMills theory. The common feature of all these theories is that they are confining and support domain walls which, in turn, are deconfining. The underlying reason for deconfinement are the underlying 't Hooft anomalies between various global symmetries of the theories. 
Tuesday 7 November 2017, 11:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepth 



Abstract:  In this talk we will present an effective field theory approach to various problems in gravitational physics. By computing scattering amplitudes in quantum gravity we derive longrange classical and quantum contributions to the gravitational bound state of two bodies. We explain how modern amplitude techniques enable much simplified computations. We describe how classical general gravity emerges from quantum loop. Using an eikonal procedure we extract postNewtonian general relativity correction as well as long range quantum corrections. We will explain why these quantum effects are universal to any quantum gravity and independent of the highenergy completion. 
Tuesday 7 November 2017, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 


Tuesday 7 November 2017, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  The thermal relic abundance of the dark matter is now determined observationally to a per cent level accuracy. It is also an increasingly useful tool to exclude, constrain or motivate models beyond the Standard Model of particle physics. It comes then with no surprise that in the recent years a considerable effort has been made to revise and improve some of the aspects of thermal relic density calculations. In this talk I will discuss some of the recent advances in such calculations, with special emphasis on the validity of an assumption of local thermal equilibrium. I will describe a refined formalism relying on the inclusion of higher moments of the Boltzmann equation and compare it to an approach based on solving the evolution of the phase space distribution function fully numerically. 
Tuesday 7 November 2017, 16:30 at DPTPHYSENS, Conf. IV, 24 Rue Lhomond, ENS Paris  SEMEXCEP (Séminaire exceptionel)  condmat.statmech 



Abstract:  Nonequilibrium quantum physics has become one of the central fields of research in particular due to an impressive degree of control in recent cold atom and quantum optics experiments. On the theoretical side, the topic provides a very fruitful playground where many seemingly diverse fields of theoretical and mathematical physics meet and overlap, such as condensed matter theory, statistical mechanics and field theory, string theory, quantum information, and dynamical systems. Having relevant and nontrivial exactly solvable models displaying key universal phenomena is a crucial aspect of every successful theory. In nonequilibrium quantum interacting manybody systems, such exact solutions have been very rare, and only very recently substantial progress has been made. In this talk I will describe one thread of recent progress, which started from exact solutions of boundary driven master equations of interacting quantum spin chains and ended up in discovering new families of quasilocal conservation laws. The latter are relevant for describing equilibration after quantum quenches and rigorously establishing ballistic or diffusive high temperature transport in integrable systems. 
Wednesday 8 November 2017, 10:00 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire de Géométrie Arithmétique ParisPékinTokyo )  MATHIHES (TBA)  hepth 



Abstract:  Bloch and Kato formulated conjectures relating sizes of padic Selmer groups with special values of Lfunctions. Iwasawa theory is a useful tool for studying these conjectures and BSD conjecture for elliptic curves. For example the Iwasawa main conjecture for modular forms formulated by Kato implies the Tamagawa number formula for modular forms of analytic rank 0. In this talk I'll first briefly review the above theory. Then we will focus on a different Iwasawa theory approach for this problem. The starting point is a recent joint work with Jetchev and Skinner proving the BSD formula for elliptic curves of analytic rank 1. We will discuss how such results are generalized to modular forms. If time allowed we may also explain the possibility to use it to deduce BlochKato conjectures in both analytic rank 0 and 1 cases. In certain aspects such approach should be more powerful than classical Iwasawa theory, and has some potential to attack cases with bad ramification at p. 
Wednesday 8 November 2017, 10:00 at LPT, salle 114 bat 210 1er etage  WORKCONF (Workshop or Conference)  hepph 


Wednesday 8 November 2017, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  TBA TBA 
Thursday 9 November 2017, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  In its simplest version, the Weak Gravity Conjecture (WGC) states that, in any sensible effective field theory coupled to gravity, there are light particles whose chargetomass ratio is larger than that of an extremal black hole. This conjecture, together with its generalizations to axions and other fields, has the potential to constrain effective field theories of phenomenological interest, like models of large field inflation, clockwork, or relaxation. However, a number of loopholes complicate this task. After a brief survey of the relevant versions of the WGC, I will explain the difficulties in obtaining precise constraints for EFT’s, and how some of these may be ameliorated by additional input of stringy physics. Finally, I will describe what can be learned from looking at the WGC from a holographic perspective. 
Thursday 9 November 2017, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  It is conventional to associate quantum gravity physics with the Planck mass energy scale and to argue that, by the principle of separation of scales, it is not important at energy scales that are much lower. I will discuss recent work on when this expectation breaks down. For example, in the presence of a weakly coupled gauge field or when scalar fields undergo superPlanckian field variations. I will also discuss new ideas on the possibility that the principle of separation of scales does not apply to quantum gravity, so that it exhibits UV/IR mixing, with potential implications for naturalness and the hierarchy problem. 
Thursday 9 November 2017, 10:00 at LPT, salle 114 Bat 210 1er etage  WORKCONF (Workshop or Conference)  hepph 


Thursday 9 November 2017, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmech 



Abstract:  In the presence of a strong magnetic field, and for an integer filling of the Landau levels, Coulomb interactions favor a ferromagnetic groundstate. It has been shown already twenty years ago, both theoretically and experimentally, that when extra charges are added or removed to such systems, the ferromagnetic state becomes unstable and is replaced by spin textures called Skyrmions. We have generalized this notion to an arbitrary number d of internal states for the electrons, which may correspond to the combination of spin, valley, or layer indices. The first step is to associate a many electron wavefunction, projected on the lowest Landau level, to any classical spin texture described by a smooth map from the plane to the projective space CP(d1). In the large magnetic field limit, we assume that the spin texture is slowly varying on the scale of the magnetic length, which allows us to evaluate the expectation value of the interaction Hamiltonian on these many electron quantum states. The first non trivial term in this semiclassical expansion is the usual CP(d1) nonlinear sigma model, which is known to exhibit a remarkable degeneracy of the many electron states obtained from holomorphic textures. Surprisingly, this degeneracy is not lifted by reintroducing quantum fluctuations. It is eventually lifted by the subleading term in the effective Hamiltonian, which selects a hexagonal Skyrmion lattice and therefore breaks both translational and internal SU(d) symmetries. I will show that when the space manifold is a torus, these optimal classical textures can be interpreted in an appealing way using geometric quantization. 
Friday 10 November 2017, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/194 )  COURS (Cours)  condmat 



Abstract:  The complex behavior of a large variety of systems can often be ascribed to the competition of many quasioptimal equilibria. In these cases metastability deeply affects both the structural and dynamical properties. Glasses are the prototype of such systems, with glassy behavior arising not only in condensed matter but also in a wide variety of fields ranging from optimization to computer science. \par In these lectures I will introduce different kinds of glassy systems and I will describe their fundamental similarities, which emerge from their statistical description. Then I will focus on a representative model, the random perceptron, and I will discuss the main techniques that can be used to solve it. \par These techniques provide a versatile theoretical toolbox that can be applied to several problems such as for example the physics of the jamming transition, its interpretation in the context of constraint satisfaction, as well as the design of new efficient algorithms to solve statistical problems. \\ 1.Introduction to glassy systems: structural glasses and constraint satisfaction problems. \\ 2.The random perceptron model. The replica approach. The replica symmetric solution and phase diagram. \\ 3.Replica symmetry breaking and marginal stability. The full RSB solution of the random perceptron. \\ 4.The jamming transition as a satisfiability threshold; critical exponents. \\ 5.Belief propagation approach and the algorithmic version of the ThoulessAndersonPalmer equations. \\ Supported by ``Investissements d'Avenir'' LabEx PALM (ANR10LABX0039PALM)  
Attachments: 
Tuesday 14 November 2017, 11:30 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  I will give a short introduction into a frameindependent formulation of Newtonian gravity, called NewtonCartan Gravity, and explain why there is a renewed interest into nonrelativistic gravity. As a particular application I will discuss a recent proposal for an Effective Field Theory describing a massive spin2 mode (the socalled GMP mode) in the Fractional Quantum Hall Effect. 
Tuesday 14 November 2017, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  The radiative decay of sterile neutrinos with typical masses of 10 keV is investigated in the presence of a strong magnetic field and degenerate electron plasma. The modification of the photon dispersion relation by the active external medium is taken into account. The limiting cases of relativistic and nonrelativistic plasma are analyzed. The decay rate in a strongly magnetized plasma as a function of the plasma electron number density is compared with the unmagnetized case. It Was found that the strong magnetic field suppresses the catalyzing influence of the electron plasma on the decay rate. 
Tuesday 14 November 2017, 17:15 at DPTPHYSENS, Salle Dussane (45 rue d'Ulm)  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  condmat.soft 


Friday 17 November 2017, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/194 )  COURS (Cours)  condmat 



Abstract:  The complex behavior of a large variety of systems can often be ascribed to the competition of many quasioptimal equilibria. In these cases metastability deeply affects both the structural and dynamical properties. Glasses are the prototype of such systems, with glassy behavior arising not only in condensed matter but also in a wide variety of fields ranging from optimization to computer science. \par In these lectures I will introduce different kinds of glassy systems and I will describe their fundamental similarities, which emerge from their statistical description. Then I will focus on a representative model, the random perceptron, and I will discuss the main techniques that can be used to solve it. \par These techniques provide a versatile theoretical toolbox that can be applied to several problems such as for example the physics of the jamming transition, its interpretation in the context of constraint satisfaction, as well as the design of new efficient algorithms to solve statistical problems. \\ 1.Introduction to glassy systems: structural glasses and constraint satisfaction problems. \\ 2.The random perceptron model. The replica approach. The replica symmetric solution and phase diagram. \\ 3.Replica symmetry breaking and marginal stability. The full RSB solution of the random perceptron. \\ 4.The jamming transition as a satisfiability threshold; critical exponents. \\ 5.Belief propagation approach and the algorithmic version of the ThoulessAndersonPalmer equations. \\ Supported by ``Investissements d'Avenir'' LabEx PALM (ANR10LABX0039PALM)  
Attachments: 
Tuesday 21 November 2017, 11:30 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  Fourdimensional N=1 vacua of Ftheory are determined by three discrete choices. A topological type of elliptically fibered CalabiYau fourfolds, a choice of flux and a minimum of the corresponding scalar potential. While there are several constructions that provide an abundance of elliptic CalabiYau the choice of properly quantized flux is in general more involved. We will start with a review of Ftheory and the geometry of CalabiYau fourfolds. We then describe how homological mirror symmetry can be used to determine properly quantized choices for a particular class of fluxes. As an application in topological string theory we discuss modular properties of the GromovWitten potentials on nonsingular CalabiYau fourfolds. (based on 1709.02820 ) 
Tuesday 21 November 2017, 14:00 at APC, 483 A  Malevitch83 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  A model suited for calculating correlation functions in QCD from the ultraviolet to the infrared is reviewed. The model consist in standard FaddeevPopov Lagrangian for Landau gauge with an extra mass term for gluons. It is shown that once this mass term is included, two and three point correlation functions can be calculated with good precision at oneloop order even at very low momenta in the quenched approximation. After that, the inclusion of quarks is analyzed. It is shown that in that case, the perturbative calculation only gives the qualitative behavior in some correlation functions. In particular, it is shown that the analysis of spontaneous chiral symmetry breaking requires to go beyond perturbation theory. A non perturbative scheme but controlled by two small parameters is discussed and the corresponding results are shown to agree with high precision to Monte Carlo numerical simulations also in the quark sector. 
Wednesday 22 November 2017, 14:00 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  Liouville conformal field theory (LCFT hereafter), introduced by Polyakov in his 1981 seminal work "Quantum geometry of bosonic strings", can be seen as a random version of the theory of Riemann surfaces. LCFT appears in Polyakov's work as a 2d version of the Feynman path integral with an exponential interaction term. Since then, LCFT has emerged in a wide variety of contexts in the physics literature and in particular recently in relation with 4d supersymmetric gauge theories (via the AGT conjecture). A major issue in theoretical physics was to solve the theory, namely compute the correlation functions. In this direction, an intriguing formula for the three point correlations of LCFT was proposed in the middle of the 90's by DornOtto and ZamolodchikovZamolodchikov, the celebrated DOZZ formula. The purpose of the course is twofold (based on joint works with F. David, A. Kupiainen and R. Rhodes). First, I will present a rigorous probabilistic construction of Polyakov's path integral formulation of LCFT. The construction is based on the Gaussian Free Field. Second, I will show that the three point correlation functions of the probabilistic construction indeed satisfy the DOZZ formula. This establishes an explicit link between probability theory (or statistical physics) and the socalled conformal bootstrap approach of LCFT. 
Thursday 23 November 2017, 11:00 at LPTHE, bibliothèque  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  mathmath.MP 


Thursday 23 November 2017, 14:00 at LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  mathph 



Abstract:  TBA 

[ English version ] 