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 ] 
Wednesday 22 February 2017, 11:00 at IPHT, Room 35  STRINT (Strings, integrability and beyond)  hepth 



Abstract:  In this talk, I will discuss entanglement entropy of integrable field theories in 1+1 dimensions in the presence of line defects which preserves integrability. For interacting field theories, integrable defects are topological while for free theories the defects can be nontopological. Using the replica trick and the form factor bootstrap method of integrable field theories, I will show that topological defects do not modify the UV behavior of the bulk entanglement entropy but lead to different corrections in the IR limit. On the contrary, nontopological defects modify both the UV and IR behavior of the bulk entanglement entropy. 
Wednesday 22 February 2017, 14:15 at IPHT, Room 35  STRINT (Strings, integrability and beyond)  hepth 



Abstract:  By recasting 4 point function by the usual confomal block expansion in terms of structure constants, we initiate the study of fourpoint functions of large BPS operators at any value of the coupling. We use the hexagon formalism to compute the structure constants. By using the nested bethe ansatz, we can compute the matrix part of the hexagon form factors for higher rank subgroups of psu(2,24). 
Wednesday 22 February 2017, 14:30 at IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  We study the role of the DingIoharaMiki (DIM) algebra, which is the simplest example of quantum toroidal algebra, in gauge theories, matrix models, qdeformed CFT and refined topological strings. We use DIM algebra to write down the Ward identities for the matrix models and show how it is connected to quiver Walgebras of the Aseries. We describe the integrable structure of refined topological strings arising from DIM algebra: the Rmatrix, Toperators and RTT relations. Finally, we write down the qKZ equation for the DIM algebra intertwiners and interpret its solutions as refined topological string amplitudes. 
Thursday 23 February 2017, 10:00 at IHP, Amphitheatre Darboux  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  Black holes are related to thermal states in strongly coupled systems. I will present some ideas about the interpretation of the region behind the horizon in statistical mechanics and the classification of non equilibrium states. 
Thursday 23 February 2017, 11:45 at IHP, Amphitheatre Darboux  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  The strongly coupled D1D5 conformal field theory is a microscopic model of black holes which is expected to have chaotic dynamics. We study the weak coupling limit of the theory where it is integrable rather than chaotic. In this limit, the operators creating microstates of the lowest mass black hole are known exactly. We consider the timeordered twopoint function of light probes in these microstates, normalized by the same twopoint function in vacuum. These correlators display a universal earlytime decay followed by latetime sporadic behavior. To find a prescription for temporal coarsegraining of these late fluctuations we appeal to random matrix theory, where we show that a progressive timeaverage smooths the spectral form factor (a proxy for the 2point function) in a typical draw of a random matrix. This coarsegrained quantity reproduces the matrix ensemble average to a good approximation. Employing this coarsegraining in the D1D5 system, we find that the earlytime decay is followed by a dip, a ramp and a plateau, in remarkable qualitative agreement with recent studies of the SachdevYeKitaev (SYK) model. We study the timescales involved, comment on similarities and differences between our integrable model and the chaotic SYK model, and suggest ways to extend our results away from the integrable limit. 
Thursday 23 February 2017, 14:00 at LPT, Salle cosmologie (110) LPT Orsay bat 210 1er etage  SEMLPT (Séminaire de Physique des Particules du LPT)  hepth 



Abstract:  The space based interferometer LISA has a great potential in probing cosmology. This talk presents two observables through which LISA could provide us with new information on the characteristics of the universe, complementary to what can be gathered from electromagnetic observations : the detection of a stochastic background of gravitational waves coming from the very early universe, and the use of massive black hole binaries as standard sirens to test the expansion of the universe. 
Thursday 23 February 2017, 16:00 at LPT, 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  We present the effective theory of a generic class of hidden sectors where supersymmetry is broken together with an approximate Rsymmetry at low energy. The light spectrum contains the gravitino and the pseudoNambuGoldstone boson of the Rsymmetry, the Raxion. We derive new modelindependent constraints on the Raxion decay constant for Raxion masses ranging from GeV to TeV, which are of relevance for hadron colliders, lepton colliders and Bfactories. The current bounds allow for the exciting possibility that the Raxion will be the first sign of SUSY. We point out the most distinctive signals of the Raxion, providing a new experimental handle on the properties of the hidden sector. 
Friday 24 February 2017, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/166 )  COURS (Cours)  astrophhepth 



Abstract:  Graphs, at their most abstract, provide a language for describing relationships, one which has long been beneficial for the program of physical prediction. Combined with the Wilsonian understanding of effective field theory, perturbative analysis finds a role in predictions relevant to all scales, from processes describing the scattering of primordial gravitons, to QCD interactions at CERN's Large Hadron Collider, to establishing the astrophysical inspiral and consequent postmerger ringing out of black holes, to the evolution of the largest scales cosmologically conceivable. Modern advances in scattering amplitude calculation have reemphasized the role of graphical organization towards efficient prediction, generalizing away from brute Feynman calculation, but yielding structural insights suggestive of a new type of unification touching predictions relevant to all of these scales. \par In these lectures I will talk about graphical organization of perturbative prediction, emphasizing scattering amplitudes, but with an eye towards generalization. \\  GENERALIZED UNITARITY METHODS. How verification can be inverted towards construction. 1 lecture. \\  COLORKINEMATICS (``BCJ'') DUALITY AND ASSOCIATED DOUBLECOPY. Exploring both computational advantages as well as unifying structure exposed. Relevant theories include: Chiral Pions, YangMills, QCD, BornInfeld, VolkovAkulov, Galileons, EinsteinHilbert Gravity, Open and Closed string theories. 2 lectures. \\  QCD. Generalizations particularly relevant to QCD calculations (massive, nonadjoint representations). 1 lecture. \\  GRAVITY/COSMOLOGY. Application of some of these ideas to astrophysical and cosmological classical solutions in gravity. 2 lectures.  
Attachments: 
Friday 24 February 2017, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  Measurements of gamma ray fluxes from celestial bodies is one of the pillars of dark matter searches. But have we explored all interesting options? I will argue that measurements of solar high energy gamma rays, an often overlooked channel, offers a complementary probe of dark matter dynamics. In addition, I will discuss the importance of correlated gamma ray signatures in observations of galactic and extragalactic sources, and point out novel signals (exotic) DM scenarios can provide in this context. 
Friday 24 February 2017, 16:00 at
LPT,
Salle 114 1er étage batiment 210 ( (warning : unusual day !) )  SEMLPT (Séminaire de Physique des Particules du LPT)  hepph 



Abstract:  We study a random matrix model for QCD at finite density via complex Langevin dynamics. This model has a phase transition to a phase with nonzero baryon density. We study the convergence of the algorithm as a function of the quark mass and the chemical potential and focus on two main observables : the baryon density and the chiral condensate. For simulations close to the chiral limit, the algorithm has wrong convergence properties when the quark mass is in the spectral domain of the Dirac operator. A possible solution of this problem is discussed. 
Monday 27 February 2017, 10:30 at IMPMC, Université Pierre et Marie CurieParis 6, tower 2322, 4th floor, room 401  JOURCLUB (Journal Club)  physics 



Abstract:  Our conventional understanding of spacetime, as well as our notion of geometry, break down once we attempt to describe the very early stages of the evolution of our universe. The extreme physical conditions near the Big Bang necessitate an intimate interplay between physics and mathematics. The main challenge is the construction of a theory of quantum gravity, the longsought unification of Einstein's general relativity with quantum mechanics. There are several attempts to formulate such a theory; they can be tested against experimental and observational results coming from high energy physics and astrophysics, leading to a remarkable interplay between gravity, particle physics and cosmology. 
Monday 27 February 2017, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  Hurwitz numbers are defined geometrically as enumerations of inequivalent branched covers of the Riemann sphere with specified ramification structure at the branch points. Weighted Hurwitz numbers include and generalize all previously studied special cases such as, e.g., only simple branch points (Okounkov and Pandharipande), or Belyi curves (3 branch points) or monotonic paths in the Cayley graph of the symmetric group generated by transpositions. The general classical weight consists of monomial sum symmetric functions of an arbitrary number of parameters $(c_1, c_2, \dots)$. The generating functions for such weighted Hurwitz numbers are KP or $2d$Toda $\tau$functions of hypergeometric type. The simplest quantum Hurwitz numbers are obtained by specialization to $c_i = q^i$. The weights for this case may be normalized to a probability measure that coincides with that for a Bose gas with linear energy spectrum. A further generalization consists of replacing the monomial sum symmetric functions with their Macdonald polynomial analogs. The semiclassical asymptotics $(q \to 1)$ of the simple quantum Hurwitz numbers are shown to reproduce, as leading term, the case studied by Pandharipande and Okounkov, while the zero temperature asymptotics $(q \to 0)$ have as leading term the Hurwitz numbers for Belyi curves. 
Tuesday 28 February 2017, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTGEN (Séminaire général du SPhT)  physics 



Abstract:  I report here on a series of joint works with Alessandro Zilio about systems of predators interacting with a single prey. We analyze the situation of predators like wolves that can divide up into several hostile packs. The questions are to understand the conditions under which predators segregate into packs, whether there is an advantage to have such hostile packs, and to compare the various territory configurations that arise in this context. Mathematically, we focus on the analysis of stationary states, stability issues, and the asymptotics of the system when the competition parameter becomes unbounded. This system bears some similarities with models arising in multiphase BoseEinstein condensates. 
Tuesday 28 February 2017, 11:00 at CPHT, Salle de conférences, bât. 6  IPNX (Séminaire commun de physique théorique des particules IPNCPHTX)  hepph 



Abstract:  Thermal field theory provides the natural framework to describe the thermodynamic properties and to study phase transitions of systems describe by quantum field theories, in particular, the quarkgluon plasma. However, its the perturbative realization faces important technical difficulties whenever massless bosons are considered, due to divergences in the IR sector. After briefly reviewing these IR divergences in thermal field theory, and especially the Linde problem, we analyze the IR behavior of YangMills theory in a Torus  $\mathbb{R}^2 \times S^1 \times S^1$  and show that, in this geometry, any perturbative calculation is expected to breakdown already at $\mathcal{O}(g^2)$. 
Tuesday 28 February 2017, 11:00 at LPTM, 554 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  condmat 



Abstract:  Extended coherence in quantum fluids can arise, typically in association with superfluidity, from a variety of mechanisms. Finite size twodimensional (2d) Bose gases present a subtle interplay between BoseEinstein Condensation, driven by quantum statistics, and the interactiondriven BerezinskiiKosterlitzThouless (BKT) phase transition, at which free vortices become suppressed and quasilong range order emerges. To explore the respective roles of quantum statistics and interactions, we study experimentally the critical point for the emergence of coherence in a harmonically trapped 2d Bose gas with tunable interactions. Over a wide range of interaction strengths we find excellent agreement with predictions based on the BKT theory of 2d superfluidity. This allows us to quantitatively show, without any free parameters, that the interactiondriven BKT transition smoothly converges onto the purely statistical BoseEinstein condensation (BEC) transition in the limit of vanishing interactions. 
Tuesday 28 February 2017, 14:00 at LPTENS, LPTENS Library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  The moduli space of vacua of 3d N=4 gauge theories splits essentially into two ``branches”: the Higgs branch parametrised by the vevs of hypermultiplet scalars and the Coulomb branch parametrised by the vevs of dressed monopole operators. Their description as complex algebraic varieties follows from ring relations for the gauge invariant chiral operators. I will present a new approach to the analysis of the Higgs and Coulomb branches based on the type IIB brane realisation of the gauge theory. Focusing on abelian theories, I will show how the addition of new ingredients in the brane setup leads to the path integral insertion of Higgs or Coulomb operators. I will explain how this construction can be used to derive the ring relations and study mirror symmetry. 
Tuesday 28 February 2017, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  Galileon models follow the Horndeski systematic construction to couple additional fields to gravity in order to modify the Einstein equations. There were first investigated from 2009 in the case of a single scalar field. Thus, there have been an increasing interest in similar models involving either a vector field or several scalar or vector fields. During this talk, I will present results from these different topics. After a review of the scalar Galileon case, I will present the vector Galileon model that is now complete, making explicit its construction and properties, as well as its coupling to gravity. We will then discuss the construction of multifields vector Galileon models, and present a systematic investigation method performed in order to obtain all the possible terms at a given order. I will finally examine more indepth the construction of scalar multiGalileon theories, and introduce in a natural way a new class of terms. This new class explains the discrepancies between the previous formulation of multiGalileon and recent papers finding additional terms. This will allow us to describe what could be the most general theory for scalar multiGalileons. 
Tuesday 28 February 2017, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  Future Dark Matter direct detection experiments will face the problem of detecting the neutrino floor, i.e. the irreducible background coming from the coherent scattering of solar neutrinos off nuclei. I will show that, contrary to the common lore, if there exists new physics which communicate with both the dark matter and the neutrino sector, the region of parameter space in which dark matter detection can be claimed is reduced even above the neutrino floor. 
Wednesday 1 March 2017, 10:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  Let X be a semistable arithmetic surface of genus at least two and $\omega$ the relative dualizing sheaf of X, equipped with the Arakelov metric. Parshin and MoretBailly have conjectured an upper bound for the arithmetic selfintersection of $\omega$. They proved that a weak form of the abc conjecture follows from this inequality. We shall discuss a way of making their conjecture more precise in order that it implies the full abc conjecture (a proof of which has been announced by Mochizuki). 
Wednesday 1 March 2017, 14:00 at LPT, L'amphi 1  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 


Wednesday 1 March 2017, 14:30 at IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  In the first part of the talk, I will discuss a joint project with Chris Elliott on realizing the geometric Langlands correspondence as an instance of Sduality by careful analysis of Kapustin and Witten's work using derived algebraic geometry. In the second part of the talk, I will report on work in progress to produce new instances of Langlands duality in geometric representation theory through the lens of quantum field theory. 
Wednesday 1 March 2017, 16:30 at LPT, salle 114, Bat 210, 1er etage, LPT Orsay  SEMLPT (Séminaire de Physique des Particules du LPT)  hepph 



Abstract:  General Relativity has been a successful theory for more than one century now. I will briefly review its accomplishments. However, most of the talk will be devoted to the reasons  both observational and theoretical that encourage us to modify our current theory of gravity. I will discuss some alternative theories of gravity and their implications. Among these, I will focus on the addition of one scalar degree of freedom to standard GR. We will see some implications for cosmology and black holes. 
Thursday 2 March 2017, 11:00 at LPTHE, Bibliothèque  SEMINFOR (Séminaire informel)  condmat.statmech 



Abstract:  Socalled 'bad metals' present a longstanding conundrum to theory. In particular, their electric resistivity is too high to be accounted for by weakly coupled quasiparticles as in conventional metals. In this talk, I will argue that ac and dc transport in the bad metallic regime can be explained by a long wavelength description of fluctuating charge density waves. Both ac and dc transport are governed by Planckian dynamics, which suggests that quantum fluctuations play an important role. I'll conclude by mentioning how gauge/gravity duality can be used to efficiently calculate conductivities in the quantum critical regime. 
Thursday 2 March 2017, 13:30 at DPTPHYSENS, room Conf. IV, 24 Rue Lhomond, ENS Paris  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  astroph 



Abstract:  TBA 
Thursday 2 March 2017, 16:00 at LPT, Salle 114, 1er etage, batiment 210  SEMLPT (Séminaire de Physique des Particules du LPT)  hepph 



Abstract:  We consider scenarios of Higgs compositeness where the Higgs doublet arises as a pseudoNambu Goldstone boson. Our focus is the scalar ("radial") excitation associated with the global symmetry breaking vacuum, which we dubbed the "global Higgs”. We study the interactions of the global Higgs and show that in a wide class of Composite Higgs models its coupling to gluons can be sizable. Some LHC signatures of the global Higgs are then investigated, including decay channels into EW bosons, top quarks, and possibly boosted top partners. 
Friday 3 March 2017, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/166 )  COURS (Cours)  astrophhepth 



Abstract:  Graphs, at their most abstract, provide a language for describing relationships, one which has long been beneficial for the program of physical prediction. Combined with the Wilsonian understanding of effective field theory, perturbative analysis finds a role in predictions relevant to all scales, from processes describing the scattering of primordial gravitons, to QCD interactions at CERN's Large Hadron Collider, to establishing the astrophysical inspiral and consequent postmerger ringing out of black holes, to the evolution of the largest scales cosmologically conceivable. Modern advances in scattering amplitude calculation have reemphasized the role of graphical organization towards efficient prediction, generalizing away from brute Feynman calculation, but yielding structural insights suggestive of a new type of unification touching predictions relevant to all of these scales. \par In these lectures I will talk about graphical organization of perturbative prediction, emphasizing scattering amplitudes, but with an eye towards generalization. \\  GENERALIZED UNITARITY METHODS. How verification can be inverted towards construction. 1 lecture. \\  COLORKINEMATICS (``BCJ'') DUALITY AND ASSOCIATED DOUBLECOPY. Exploring both computational advantages as well as unifying structure exposed. Relevant theories include: Chiral Pions, YangMills, QCD, BornInfeld, VolkovAkulov, Galileons, EinsteinHilbert Gravity, Open and Closed string theories. 2 lectures. \\  QCD. Generalizations particularly relevant to QCD calculations (massive, nonadjoint representations). 1 lecture. \\  GRAVITY/COSMOLOGY. Application of some of these ideas to astrophysical and cosmological classical solutions in gravity. 2 lectures.  
Attachments: 
Monday 6 March 2017, 14:00 at
IPN,
IPN, Bâtiment 100, salle A 015 ( $$ )  IPNTHEO (Séminaire du groupe de physique théorique de l'IPN Orsay)  nuclth 



Abstract:  The interacting shell model is a powerful theoretical framework for studying the nuclear structure. Unfortunately, the combinatorial scaling of the manybody space with the number of valence nucleons or the size of the singleparticle basis strongly restricts its applicability. Quantum MonteCarlo (QMC) methods may then be considered as attractive techniques to overcome such limitations by offering an alternative to the diagonalization of the Hamiltonian. In this context, I will present a new QMC approach for the shell model yielding nearly exact spectroscopies of nuclei. The originality of the formalism lies in the use of a variational symmetryrestored wave function to 'guide' the Brownian motion, as well as to control the sign/phase problem that generally makes the traditional QMC samplings totally ineffective by causing a prohibitive growth of the statistical errors.  
Attachments: 
Tuesday 7 March 2017, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTGEN (Séminaire général du SPhT)  physics 



Abstract:  Our intuition for how quantum field theories behave is guided by the principle of naturalness. This principle, which relies merely on the zeropoint energy of quantum systems, states that generic quantum field theories are wellcharacterized by dimensional analysis, unless contraints from symmetries intervene. But current null results from the Large Hadron Collider seem to suggest that particle physics (without gravity) is described by the Standard Model, a highly unnatural quantum field theory. The new question in particle physics is ''what is the question?'' Are there experimental violations of the Standard Model at the LHC that we have missed, or that we will find eventually using advanced methods? Or is the LHC's result truly null? If so, why has the principle of naturalness failed? Are we dealing with a theoretical subtlety, a selection bias, or some other consequence of cosmological history? 
Tuesday 7 March 2017, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  AirCherenkov telescopes have mapped the Galactic plane at TeV energies. Here we evaluate the prospects for detecting the neutrino emission from sources in the Galactic plane assuming that the highest energy photons originate from the decay of pions. Four promising sources are identified based on having a large flux and a flat spectrum. We subsequently evaluate the probability of their identification above the atmospheric neutrino background in IceCube data as a function of time. We show that observing them over the twentyyear lifetime of the instrumentation is likely, and that some should be observable at the 3 sigma level with six years of data. In the absence of positive results, we derive constraints on the spectral index and cutoff energy of the sources, assuming a hadronic acceleration mechanism. 
Tuesday 7 March 2017, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepphhepth 



Abstract:  Large and discrete gauge transformations can be converted to global symmetries by coupling the original theory to a topological model. I comment on the relevance of this remark for sphaleroninduced processes in the Standard Model, and for axionmonodromy models of inflation. 

[ English version ] 