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 ]  
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Monday 16 December 2019, 09:30 at IHP, Amphi Darboux  WORKCONF (Workshop or Conference)  hepth 



Abstract:  Bernard has made many significant contributions to science, amongst which the description of supergravity in eleven dimensions (with Eugene Cremmer and Joël Scherk), the JuliaZee dyon as well as dualities in supergravity. Bernard's contributions have been farsighted. We foresee two days of exciting science to honour the multifaceted career of our friend and colleague Bernard Julia. Program at https://bernardjulia.sciencesconf.org/program 
Monday 16 December 2019, 10:45 at LPTMC, Jussieu campus, tower 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  The Hall coefficient has long been used to characterise the number and sign of charge carriers in metals and semiconductors. This assignment has only been justified in the weak disorder and interactions regimes. Unexpected Hall coefficient sign reversals (a.k.a. ``Hall anomalies’’) have been observed in strongly interacting metals, flux flow regime of superconductors and thermal Hall effect in antiferromagnets. I describe recent theoretical developments which shed light on Hall anomalies: New computable formulas for the Hall and thermal coefficients of gapless metals, and a revised theory of fluxflow conductivity. Hall anomalies are found to be produced by proximity to Mott insulator phases, topological density fluctuations in antiferromagnets, and by moving vortex charge in superconductors. 1.Equilibrium formulae for transverse magnetotransport of strongly correlated metals <https://phsites.technion.ac.il/publications/assa/Phys_Rev_B99_115115.pdf>, A. Auerbach, Phys. Rev. B 99, 115115 (2019). 2.Hall Number of Strongly Correlated Metals <https://phsites.technion.ac.il/publications/assa/Phys_Rev_Lett_121_066601.pdf>, A. Auerbach, Phys. Rev. Lett. 121, 066601 (2018). 3. Ilia Khait and A. Auerbach, in preparation. 4. Noga Basha and A. Auerbach, in preparation. 5. A. Auerbach and Dan Arovas, in preparation. 
Monday 16 December 2019, 13:30 at LPENS, Conf IV  LPA (Séminaire du laboratoire Pierre Aigrain)  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. 
Tuesday 17 December 2019, 09:30 at IHP, Amphi Darboux  WORKCONF (Workshop or Conference)  hepth 



Abstract:  Bernard has made many significant contributions to science, amongst which the description of supergravity in eleven dimensions (with Eugene Cremmer and Joël Scherk), the JuliaZee dyon as well as dualities in supergravity. Bernard's contributions have been farsighted. We foresee two days of exciting science to honour the multifaceted career of our friend and colleague Bernard Julia. Program at https://bernardjulia.sciencesconf.org/program 
Tuesday 17 December 2019, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  The observed dark matter (DM) abundance in the Universe can be fully accounted for by a minimally coupled spectator scalar field that was light during cosmic inflation. In this scenario, dark matter was produced during inflation by amplification of quantum fluctuations of the spectator field. I will discuss the DM isocurvature perturbations that are unavoidably generated in such scenarios and the circumstances under which they are not problematic for the viability of nonthermal DM models. I will also discuss implications of DM isocurvature for structure formation, showing that the model has interesting consequences which allow one to test the scenario. 
Wednesday 18 December 2019, 10:00 at IHES, Centre de conférences Marilyn et James Simons  MATHIHES (TBA)  hepth 



Abstract:  I would like to explain a classification result for pdivisible groups, which unifies many of the existing results in the literature. The main tool is the theory of prisms and prismatic cohomology recently developed by Bhatt and Scholze. This is joint work with Johannes Anschütz. 
Wednesday 18 December 2019, 12:00 at LPENS, Conf. IV  FORUMENS (Forum de Physique Statistique @ ENS)  condmat.statmech 



Abstract:  Abelian sandpiles, looperased random walks, and chargedensity waves at depinning all belong to the same universality class, as does the O(n) model at n=2. The equivalences between these systems are exciting, as they related models with quenched disorder, cellular automata, and the classical O(n) symmetric phi^4 theory for which we know results up to 7 loops. 
Wednesday 18 December 2019, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  I will look at the structure of generic D=4, N=1 Minkowski flux backgrounds of string theory via generalised geometry. I will show how we can completely characterise the geometry via integrable Gstructures and the objects defining them. We will be able to give expressions for the Kahler and superpotential of the lower dimensional effective theory in terms of these objects. Moreover I will give an analysis of the moduli of these structures, recovering the known results for G2 manifolds as well as extending results for GMPT and socalled 'type 0' solutions. In looking at the moduli we will find that there is a subtlety involving a quotient by a complexified group. Upon a closer look we will see that understanding the full picture will leads us to some interesting possible links with Geometric Invariant Theory and G2 stability. 
Wednesday 18 December 2019, 16:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  I will describe the Cosmological Bootstrap  an approach to compute correlation functions of primordial fluctuations based on symmetries and singularities. Using this approach, I will present some new results for inflationary three and fourpoint functions of scalars and tensors. These shapes do not depend on the specific inflationary model, as long as the fluctuations minimally break de Sitter symmetry 
Thursday 19 December 2019, 10:00 at IHP, Salle 314  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  I will prove a theorem about 2D CFTs: Every unitary 2D CFT must contain a nontrivial Virasoro primary of scaling dimension at most c/8 + 1/2, where c is the central charge. At large c, this is an improvement of the Hellerman bound c/6 + O(1), and is relevant for constraining the spectrum of gravitational theories in AdS3. The proof follows from the modular bootstrap and uses analytic extremal functionals, originally developed in the context of fourpoint SL(2) conformal bootstrap. In the second part of the talk, I will discuss a surprising connection between modular bootstrap and the spherepacking problem from discrete geometry. In particular, the above bound on the gap becomes a bound on the spherepacking density. In 8 and 24 dimensions, this bound is sharp and leads to a solution of the spherepacking problem in these dimensions, as originally proved by Viazovska et al. 
Thursday 19 December 2019, 15:00 at LPTMC, Jussieu tower 1312 5th floor room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  In this talk, I will recall some results I got during my PhD and show new results obtained since then. In a second part, I will present part of the results I got during my postdoc in Geneva. The question of firstpassage time, typically the time needed for two particles to encounter, is of importance to quantify the rate of reaction of any diffusionlimited process. If the problem is essentially solved for markovian (that is memoryless) random walks such as brownian motion, only sparse results do exist for nonmarkovian random walks. I will present a formalism we have developed to quantify the mean first passage time to a target for a confined nonmarkovian random walker, whose position statistics is gaussian and with stationary increments. Then, I will present some features of confined ageing processes (that is : if the stationary increments hypotheses is relaxed), and decipher the links with the associated unconfined processes. In particular, the importance of the socalled persistance exponent will be emphasised. I will finally show how our gaussian formalism can be extended to ageing unconfined processes in order to get the value of the persistance exponent. In a second part, I will present a physical description of the actin cytoskeleton, which is a layer of fibers in interaction with molecular motors. This layer is polymerizing along the plasma membrane. Usual model typically see it as a thin layer, that is neglecting the dynamics in the direction orthogonal to the membrane. I will show that a more precise description that account for this direction leads to a new instability mechanism that cannot be observed within the thinlayer approach. Finally, I will briefly mention experimental works in agreement with this predicted instability. 
Friday 20 December 2019, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Friday 20 December 2019, 15:00 at IPHT, Amphi Claude Bloch, Bât. 774  SOUTENHDR (Soutenance d'Habilitation à Diriger des Recherches)  physics 


Monday 6 January 2020, 10:45 at LPTMC, Jussieu tower 1312 5th floor room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Thursday 9 January 2020, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 9 January 2020, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 9 January 2020, 14:00 at LPTMC, Jussieu tower 1312 5th floor room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Friday 10 January 2020, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 


Tuesday 14 January 2020, 11:00 at CPHT, Salle Louis Michel  SEMCPHT (Séminaire du CPHT)  hepth 


Wednesday 15 January 2020, 14:15 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://www.ipht.fr/Phocea/Vie_des_labos/Seminaires/index.php?id=993966 )  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Thursday 16 January 2020, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepthmath 



Abstract:  Classical genus zero proposes a duality phenomenon for CalabiYau (CY) manifolds, relating the Yukawa coupling for a large structure limit of CY's and enumerative invariants of rational curves on a mirror CY. For the higher genus counting problem, the corresponding conjectural program was proposed by BershadskyCecottiOoguriVafa (BCOV). In particular, they predict that a combination of holomorphic analytic torsions of large structure limits of CY's encapsulate genus one enumerative invariants on a mirror. In this talk I would like to present and discuss a refined conjecture which bypasses spectral theory and pertains to the realm of complex geometry, as for the Yukawa coupling. I will then explain a proof of this conjecture for the mirror family of CalabiYau hypersurfaces in projective space, which relies on the arithmetic RiemannRoch theorem in Arakelov geometry. The result is compatible with the BCOV predictions, as well as related work by Zinger. 
Friday 17 January 2020, 11:00 at APC, Amphithéatre Pierre Gilles de Gennes  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  I will present the stageIV Dark Energy Spectroscopic Instrument (DESI). The scientific goals of DESI on dark energy, redshift space distortions and constraints on inflation or neutrino mass will be compared to current measurements and limits set by ongoing experiments, in particular by the SDSS BOSS and eBOSS projects. I will illustrate the construction status of DESI, which is nearing completion, and give the timeline of the fiveyear survey. The project has successfully observed its first spectroscopic light and is now under commissioning. When it will enter survey mode, DESI is expected to be one of the world’s best facilities for wide field spectroscopy throughout the decade. 
Friday 17 January 2020, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 


Tuesday 21 January 2020, 11:00 at CPHT, Salle Louis Michel  SEMCPHT (Séminaire du CPHT)  hepth 


Wednesday 22 January 2020, 14:30 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  hepth 



Abstract:  Filtration by ramification groups of the Galois group of an extension of local fields with possibly imperfect residue fields is defined by Abbes and the speaker. The graded quotients are abelian groups and annihilated by the residue characteristic in the general case. We discuss the main ingredients of the proof and the construction of injections of the character groups of the graded quotients. 
Thursday 23 January 2020, 10:00 at LPTHE, LPTHE Library  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 23 January 2020, 11:40 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  (based on 1906.09228 ) 
Tuesday 28 January 2020, 11:00 at CPHT, Salle Louis Michel, CPHT, Ecole Polytechnique  SEMCPHT (Séminaire du CPHT)  hepth 



Abstract:  I consider a model of fluid particle motion given by the reconstructed KdV equation on a circle. For travelling waves that are "uniformizable" in a suitable sense, the map that governs stroboscopic motion can be derived analytically. The particle's drift velocity, then, is essentially the Poincaré rotation number of that map, and has a geometric origin: it is the sum of a dynamical phase, a geometric/Berry phase, and an "anomalous phase". The last two phases are universal, as they follow entirely from the underlying Virasoro group structure. The Berry phase, in particular, is produced by a sequence of adiabatic conformal transformations due to the moving wave profile, and was previously found in twodimensional conformal field theories. 
Tuesday 28 January 2020, 11:30 at LPTHE, LPTHE library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 


Friday 31 January 2020, 11:00 at APC, 454A  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 


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