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 29 January 2020, 11:30 at IJCLAB, 015  NUCTHEO (Séminaire de physique nucléaire théorique)  nuclth 



Abstract:  The extension of nuclear physics to the strange sector is a difficult challenge due to the shortage of experimental data, and the difficulty in solving QCD at low energies. With the forthcoming new facilities and new experiments dedicated to the study of single and doublelambda hypernuclei we prospect new and important developments in this field in the very near future. Reliable theories are essential to support and analyze these experimental campaigns. In this talk, we present the first comprehensive application of pionless effective field theory to single and double $\Lambda$ hypernuclei composed of up to 6 baryons. The theory, fitted to reproduce available experimental data, solves the longstanding overbinding problem of the $^5_\Lambda$He hypernucleus and predicts the existence of a fivebody double$\Lambda$ Hypernuclear bound state yet to be found. Pionless effective field theory is revealed to be a very successful approach to hypernuclei due to the small number of free parameters, and the good theoretical accuracy, enhanced by the large breaking scale and the small momentum of the lambda particles. 
Wednesday 29 January 2020, 16:00 at LPENS, Conf IV  LPENSACE (Astronomy and Cosmology at ENS)  astroph 



Abstract:  Do all spiral galaxies exhibit coherent magnetic fields? How are galactic magnetic fields amplified and maintained? What is the distribution of field strengths? How did this change with time? In this talk, I address these questions using a model which computes the magnetic properties of a statistical sample of evolving galaxies. It employs a semianalytic model of galaxy formation to produce realistic timevarying galactic properties and numerically solves the dynamo equations from the early universe until the present. I will also discuss what are the prospects for observationally constraining this and similar models using a range of tracers. 
Wednesday 29 January 2020, 17:00 at LPENS, Conf IV  LPENSACE (Astronomy and Cosmology at ENS)  astroph 



Abstract:  About half of the energy emitted by stars in galaxies was absorbed by dust and reemitted in the farinfrared. This phenomenon is particularly dramatic for the UV radiation from young stars tracing the star formation. Estimating this intrinsic UV emission is key to understand the star formation across cosmic times. We thus need to know both the amount of UV and farinfrared emitted by the galaxies. During the last decade, Herschel and ALMA have pushed our knowledge of the dusty Universe up to the end of the reionization. It is now clear that very dusty objects exist very early in the Universe and a large fraction of the star formation budget at very high redshift (z~6) is still hidden by dust. I will review the main results from the last years and discuss the consequence on our understanding of galaxy formation. Finally, I will discuss how the SPICA mission can improve our knowledge of this dusty Universe. In particular, the BBOP instrument will offer us the first opportunity to detect the polarized signal from highredshift dusty galaxies. 
Thursday 30 January 2020, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepthmath.AG 



Abstract:  The K3 surfaces are complex algebraic surfaces with remarkable properties. A property that characterizes them, is the existence of a unique, up to scalar multiplication, global holomorphic two form which is never zero. In the last years their group of symmetry, the automorphisms of the K3 surfaces, aroused a lot of interest and it has been much studied. Depending on the action on the holomorphic two form, which can be trivial or not, an automorphism is called symplectic or nonsymplectic. After an introduction on the subject, the aim of the talk is to show recent results in the study of nonsymplectic automorphisms of 2power order. In particular in the case of the order 16, I give a full description of the families of K3 surfaces carrying such automorphisms. 
Friday 31 January 2020, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=en/node/246 )  COURS (Cours)  hepphhepth 



Abstract:  This series of lectures is primarily associated with collider physics where one seeks to learn about fundamental interactions by colliding particles at high energy and by studying the products of these collisions. In this sense, talking about jets is essentially talking about the highlyenergetic quarks and gluons produced in these collisions and their dynamics governed by the strong interaction. This is ubiquitous in all recent colliders and jets are (to varying degrees) present in almost all aspects of collider phenomenology. This set of lectures is mostly twofolded: on one side it will try to give a taste of the broad range of aspects and applications of jet physics, on the other side it will show how it is rooted in (perturbative) Quantum Chromodynamics (QCD). Lectures 45/5  Jet substructure in QCD:I will cover several aspects of QCD calculations in the context of jet substructure with a specific focus on their conceptual interpretation. This will cover applications to quark/gluon separation, heavyboson (W/Z/Higgs) tagging as well as a few curiosities that arise in the process of understanding jet substructure from first principles in perturbative QCD. Remarks:In terms of reference material, most of material covered in the lectures can be found in the set of Springer Lecture Notes "Looking Inside Jets: an introduction to jet substructure and boostedobject phenomenology" (arXiv:1901.10342).Some of the material covered in the first lecture can also be found in the review "Towards Jetography" (arXiv:0906.1833) as well as in standard QCD textbooks (e.g. "QCD and collider physics" by Keith Ellis, James Stirling and Brian Webber). The first and third lectures will be oriented towards concepts and phenomenological aspects. While keeping physics consequences as a target, lectures 2, 4 and 5 will focus more on calculations in the context of perturbative QCD. Note however that this is a tentative plan: I am happy to make adjustments if, in the course of the lectures, it appears that some aspects are worth exploring in more details or some different directions worth being introduced.  
Attachments: 
Friday 31 January 2020, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmech 



Abstract:  The perturbative expansions of many physical quantities are divergent, and defined only as asymptotic series. It is well known that this divergence reflects the existence of nonperturbative, exponentially damped contributions, such as instanton effects, which are not captured by a perturbative analysis. This connection between perturbative and nonperturbative contributions of a given physical observable can be systematically studied using the theory of resurgence, allowing us to construct a full nonperturbative solution from perturbative asymptotic data. In this talk I will start by reviewing the essential role of resurgence theory in the description of the analytic solution behind an asymptotic series, and its relation to the socalled Stokes phenomena and phase transitions. I will then exemplify how these techniques can be applied to to the LeeYang zeros in the context of matrix models, a subject of great interest in both mathematics and physics. 
Friday 31 January 2020, 11:00 at APC, 454A  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  With the advent of groundbased gravitational waves detectors, such as Advanced Ligo and Advanced Virgo, the era of multimessenger astrophysics from compact binary merger has started. Such a kind of events represent bright sources of gravitational waves and electromagnetic radiation, as well as neutrinos and heavy nuclei. The detection and interpretation of multimessenger signals from the collision of two compact objects requires a fruitful interplay between the observational efforts and the theoretical modeling. The pivotal role of all fundamental interactions, as well as the multiscale, multiphysics nature of the process, represents a great challenge in the path towards a deeper understanding of the coalescence process and of its rich phenomenology. In this talk, I will review our present understanding of the major processes involved in the merger of two neutron stars and on their impact on some of the many observable we can presently detect. A special emphasis will be given to the role of neutrinos and weak interactions. 
Monday 3 February 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 



Abstract:  We present an N=2supersymmetric extension [1] of JackiwPi´s chiral gauge theory (CGT) [2] originally designed to describe Dirac electrons in graphene. The augmented framework allows for the identification of nonperturbative solutions, as vortexlike configurations that saturate a topologically nontrivial (BPS )bound are proven to be. Remarkably, that regime reveals to be free from extra scalar degrees of freedom brought about to the model as needed partners to fermions in such a linear realisation of supersymmetry, but lacking a phenomenological interpretation. Furthermore, inherent RParity provides the room for incorporating a global phasefermion number symmetry already manifest in the CGT, but now regarded as an external (superspace) invariance. Comments on the fermionic massmatrix and perspectives shall compose our conclusions. [1] E.M.C. Abreu, M.A. De Andrade, L.P.G. De Assis, J.A. HelayëlNeto, A.L.M.A. Nogueira, R.C. Paschoal, Annals of Physics 354 (2015) 618–636. [2] R. Jackiw, S.Y. Pi, Phys. Rev. Lett. 98 (2007) 266402. 
Monday 3 February 2020, 13:30 at LPENS, Conf IV  LPENSMDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS)  condmat 



Abstract:  While the integration of nanocrystals for display application has demonstrated the viability of these nanomaterials for a mass market, their use for infrared sensing appears also quite promising. When infrared wavelengthes are considered, I will show that HgTe nanocrystals offer a unique combination of broadly tunable optical absorption in the infrared from 1 to 100 µm [1 and top part of figure] and photoconductive properties. However, the maturity of the current device remains far weaker what have been achieve for solar cell using PbS nanocrystals. Current limitations are the result of limited material development and poor understanding of the electronic structure of the material under colloidal form. In this talk, I will discuss some of the recent developments relative to HgTe nanocrystal integration into photodiodes operating in the short wave and mid wave infrared. I will present how the concepts of unipolar barrier has been transferred from IIIV semiconductor to colloidal HgTe nanocrystal film [2]. Another important limitation to address is tradeoff between the absorption depth (> 1 µm) and the carrier diffusion length (< 100 nm) which make that most current devices have a weak light absorption (10 % of the incident light typically). This issue can be addressed by two strategies which are the development of ink to achieve thick high mobility film [3] and by enhancing the light matter coupling thanks to the introduction of plasmonic resonator (bottom left part of figure). I will briefly also report about recent development relative to the integration into focal plane array to conduct imaging (bottom right part of figure). Finally, I will discuss about how it is possible to take advantage of intraband transitions in self doped nanocrystal to design mid wave infrared detector [45]. I will in particular discuss how early limitations of the doped nanocrystals (large dark current in particular) can be overcome by carefully engineering the energy landscape of the nanocrystal film. To reach this goal design inspired from IIV semiconductor has been used. References [1] Terahertz HgTe nanocrystals: beyond confinement, N. Goubet, A. Jagtap, C. Livache, B. Martinez, H. Portales, X. Zhen Xu, R.P.S.M. Lobo, B. Dubertret, E. Lhuillier, J. Am. Chem. Soc. 140, 5053 (2018). [2] Design of Unipolar Barrier for Nanocrystal Based Short Wave Infrared Photodiode, A.Jagtap, B. Martinez, N. Goubet, A. Chu, C. Livache, C. Greboval, J. Ramade, D. Amelot, P. trousset, A. triboulin, S. Ithurria, M. G. Silly, B. Dubertret, E. Lhuillier, ACS Phot. 5, 4569 (2018) [3] HgTe Nanocrystal Inks for Extended Short Wave Infrared Detection, B. Martinez, J. Ramade, C. Livache, N. Goubet, A. Chu, C. Gréboval, J. Qu, W. L. Watkins L. Becerra, E. Dandeu, J.L. Fave, C. Méthivier, E. Lacaze, E. Lhuillier, Adv Opt Mat 1900348 (2019). [4] Infrared photodetection based on colloidal quantumdot films with high mobility and optical absorption up to the THz, E. Lhuillier, M. Scarafagio, P. Hease, B. Nadal, H. Aubin, X. Z. Xu, N. Lequeux, G. Patriache, S. Ithurria, B. Dubertret, Nano Lett 16, 1282 (2016) [5] A Colloidal Quantum Dot Infrared Photodetector and its use for Intraband Detection, C. Livache, B. Martinez, N. Goubet, C. Greboval, J. Qu, A. Chu, S. Royer, S. Ithurria, M. G. Silly, B. Dubertret, E. Lhuillier, Nature Comm 10, 2125 (2019) 
Monday 3 February 2020, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  hepth 



Abstract:  In low dimension, it is expected that topological properties determine a natural geometry. In this spirit, several characterizations are conjectured for Kleinian groups, i.e. discrete subgroups of PSL(2,C). We will survey different methods that lead to their topological and dynamical characterizations, and point out their limits and the difficulties encountered in obtaining a complete answer. 
Monday 3 February 2020, 16:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  hepth 



Abstract:  Let W be a Coxeter group. We provide a precise description of the conjugacy classes in W, yielding an analogue of Matsumoto's theorem for the conjugacy problem in arbitrary Coxeter groups. This extends to all Coxeter groups an important result on finite Coxeter groups by M. Geck and G. Pfeiffer from 1993. In particular, we describe the cyclically reduced elements of W, thereby proving a conjecture of A. Cohen from 1994. 
Tuesday 4 February 2020, 11:00 at LPTHE, Library, tour 1314, 4th floor  P^3 (Particle Physics in Paris)  hepphhepth 



Abstract:  Effective Field Theories (EFTs) appear everywhere there is a mass scale. They serve to simplify complex multiscale problems (e.g. the theory of fermions below the electroweak scale), and they serve as general tools to parametrise the unknown or incalculable (e.g. the pion chiral Lagrangian, gravity, or physics beyond the standard model). In this sense, they are perhaps even too general (everything which is not forbidden is compulsory). In this talk I will present a tool to distinguish EFTs that can originate from microscopic unitary theories and I will show that this strongly limits the (classic and quantum) running of EFTs scattering amplitudes. In particular, Massive gravity, theories with isolated massive higherspin particles, and theories with very irrelevant interactions, cannot originate from unitary theories. 
Tuesday 4 February 2020, 11:00 at IPHT, Amphi Hermite  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  Effective Field Theories (EFTs) appear everywhere there is a mass scale. They serve to simplify complex multiscale problems (e.g. the theory of fermions below the electroweak scale), and they serve as general tools to parametrise the unknown or incalculable (e.g. the pion chiral Lagrangian, gravity, or physics beyond the standard model). In this sense, they are perhaps even too general Â (everything which is not forbidden is compulsory). In this talk I will present a tool to distinguish EFTs that can originate from microscopic unitary theories and I will show that this strongly limits the (classic and quantum) running of EFTs scattering amplitudes. In particular, Massive gravity, theories with isolated massive higherspin particles, and theories with very irrelevant interactions, cannot originate from unitary theories. Â 
Tuesday 4 February 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:  The organization of fluid systems into a turbulent layer adjacent to a stably stratified one is common both in Nature (atmospheres, stellar interiors, ...) and in the industry (e.g. nuclear power plant in accidental configurations). Understanding the exchanges of mass and momentum at the interface and the coupled dynamics of such systems is challenging, because of the large range of involved time and lengthscales, from the rapid smallscale turbulence associated to the excitation of propagating waves, to their longterm nonlinear interactions associated to largescale circulations. I will present the results of various experimental investigations of idealised configurations, complemented by numerical simulations: a turbulent jet impinging a density interface, the convection in water around 4 degree Celsius, etc. Applications in meteorology, stellar evolution, and nuclear safety, will be addressed. 
Wednesday 5 February 2020, 12:00 at LPENS, Conf. IV  FORUMENS (Forum de Physique Statistique @ ENS)  condmat.statmech 



Abstract:  Abstract: I will consider the nonequilibrium dynamics of a recently introduced class of "statistically solvable” manybody quantum systems: the dualunitary circuits. These systems furnish a minimal modelling of generic locally interacting manybody quantum systems: they are generically nonintegrable and include a quantum chaotic subclass. I will first discuss the dynamics of initialstate dependent quantities, such as the entanglement entropies and local correlators, showing that it is possible to find (and classify) a family of initial states in MPS form that allow for an exact solution of the dynamics (also in the presence of quantum chaos). Then I will discuss the dynamics of an initialstate independent quantity, the so called “operator entanglement”, that measures the growth of entanglement that the Heisenberg evolution induces in operator space. I will show that one can identify different subclasses of dual unitary circuits. In particular I will describe a “maximally chaotic” subclass, where the entanglement of local operators grows linearly, and a “dynamically constrained” one, where the entanglement of local operators is bounded. 
Wednesday 5 February 2020, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Thursday 6 February 2020, 10:00 at LPTHE, LPTHE Library  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  > This talk is dedicated to recent doublecopy constructions that unify massless treelevel amplitudes in a variety of perturbative string theories. All the polarization dependence in gauge and gravity amplitudes of typeI, typeII, bosonic and heterotic string theories is proposed to enter via fieldtheory building blocks with a known Lagrangian origin. The second doublecopy component of massless string amplitudes involves modulispace integrals over punctured sphere and disk worldsheets whose lowenergy expansion introduces multiple zeta values. At each order in the inverse string tension alpha’, the coefficients of highest transcendental weight turn out to be universal across the above perturbative string theories. These phenomena have not been explained by the known string dualities and are hoped to reflect a deeper principle in the theory of quantum gravity. 
Thursday 6 February 2020, 11:40 at LPTHE, LPTHE Library  RENCTHEO (Rencontres Théoriciennes)  hepth 


Thursday 6 February 2020, 14:00 at LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  mathph 



Abstract:  Classical chaos refers to exponential sensitivity of phasespace trajectories to small changes in initial conditions. It is not straightforward to extend this notion to quantum systems, which undergo linear evolution and moreover do not exhibit precise phase space trajectories. One possible way to define quantum chaos is via statistical properties of energy levels, which have been related to those of random matrices. Recently, motivated by studies of black holes, exponential growth of outoftimeorder correlators has received a lot of attention as another possible diagnostic of quantum chaos, and an upper bound on the corresponding “Lyapunov exponent” has been obtained. Chaos is closely related to the thermalization of isolated quantum systems. Via holography, quantum chaos is reflected in the physics of black holes, which are dual to thermal states. In the same way, the study of black hole formation has given a new handle on the thermalization of strongly correlated systems. This talk contains a review of these ideas as well as brief discussions of some recent projects in our group. 
Friday 7 February 2020, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=en/node/246 )  COURS (Cours)  hepphhepth 



Abstract:  This series of lectures is primarily associated with collider physics where one seeks to learn about fundamental interactions by colliding particles at high energy and by studying the products of these collisions. In this sense, talking about jets is essentially talking about the highlyenergetic quarks and gluons produced in these collisions and their dynamics governed by the strong interaction. This is ubiquitous in all recent colliders and jets are (to varying degrees) present in almost all aspects of collider phenomenology. This set of lectures is mostly twofolded: on one side it will try to give a taste of the broad range of aspects and applications of jet physics, on the other side it will show how it is rooted in (perturbative) Quantum Chromodynamics (QCD). Lectures 45/5  Jet substructure in QCD:I will cover several aspects of QCD calculations in the context of jet substructure with a specific focus on their conceptual interpretation. This will cover applications to quark/gluon separation, heavyboson (W/Z/Higgs) tagging as well as a few curiosities that arise in the process of understanding jet substructure from first principles in perturbative QCD. Remarks:In terms of reference material, most of material covered in the lectures can be found in the set of Springer Lecture Notes "Looking Inside Jets: an introduction to jet substructure and boostedobject phenomenology" (arXiv:1901.10342). Some of the material covered in the first lecture can also be found in the review "Towards Jetography" (arXiv:0906.1833) as well as in standard QCD textbooks (e.g. "QCD and collider physics" by Keith Ellis, James Stirling and Brian Webber). The first and third lectures will be oriented towards concepts and phenomenological aspects. While keeping physics consequences as a target, lectures 2, 4 and 5 will focus more on calculations in the context of perturbative QCD. Note however that this is a tentative plan: I am happy to make adjustments if, in the course of the lectures, it appears that some aspects are worth exploring in more details or some different directions worth being introduced.  
Attachments: 
Friday 7 February 2020, 11:00 at LPTHE, Bibliothèque  SEMLPTHE (Séminaire du LPTHE)  condmat.statmechhepthmathph 



Abstract:  The study of irrelevant perturbations has profound implications on our understanding of the space of QFTs and possesses important applications in Statistical and Condensed Matter Physics  e.g. the control on subleading corrections to the scaling limits of lattice models. In 1+1 D a partial map of the above mentioned space can be traced out thanks to the existence of integrable systems, which grant us a high degree of control on certain renormalization flows trajectories. In this talk I will present some results from a recent work concerning a large class of irrelevant perturbations that, in the framework of factorized scattering, can be described by generic deformations of the Smatrix by a CDD factor. I will show how these deformations can be described as certain fielddependent twists in the boundary conditions of the fields  a natural generalization of the geometric interpretation of the $T\bar{T}$ deformation  and that there exists a relation amongst CDD deformations and the thermodynamics of the Generalized Gibbs Ensemble. Exploiting the integrability of the models, I will derive a general flow equation for the finite size spectrum and, for the particular case of the sinhGordon model, will present a connection with the fermionic basis description of finitesize onepoint functions. 
Friday 7 February 2020, 11:00 at APC, Amphithéatre Pierre Gilles de Gennes  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 


Friday 7 February 2020, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  (TBA) 
Tuesday 11 February 2020, 11:00 at CPHT, Salle Louis Michel  SEMCPHT (Séminaire du CPHT)  hepth 


Wednesday 12 February 2020, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  Higher Spin Gravities are supposed to be minimalistic extensions of gravity that embed it into a quantum consistent theory. However, such minimality turns out to be in tension with the field theory approach, as well as with the numerous nogo theorems. We report on the recent progress in constructing Higher Spin Gravities and testing quantum effects therein. The same time, via AdS/CFT Higher Spin Gravities should be related to a variety of interesting threedimensional CFT 
Tuesday 18 February 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 18 February 2020, 17:15 at DPTPHYSENS, Amphi Jaurès  Département de Physique de l'ENS 24 rue Lhomond 75005 PARIS  COLLOQUIUMENS (Colloquium of the Physics Department of ENS)  physics 



Abstract:  Modeling fluid flows in channels is a general problem in science and engineering. For ideal liquids, the situation is simple: there is no dissipation due to fluid movement. For real liquids, some energy is lost. Navier, in his pioneering work on fluid mechanics identified two possible sources of dissipation: bulk dissipation, associated to the viscosity and the friction of the last layer of liquid molecules sliding on the solid surface. For surface dissipation, a classical assumption of fluid dynamics is that a liquid element adjacent to the surface is equal to the velocity of the surface, i.e. a nonslip boundary condition, which leads to no surface dissipation. This is not the only possibility. Navier, postulating the existence of a slip velocity at the surface, introduced the possibility of surface dissipation. He proposed a linear relation between the shear stress at the solidliquid interface and the slip velocity: σ=kV, where k is the interfacial friction coefficient. Indeed, it is also possible to define the slip length b as the distance from the solid surface where the fluid velocity profile extrapolates linearly to zero. During this presentation, I will briefly review what we know on the boundary condition for simple Newtonian liquids and show that polymers, due to their entanglements present a unique tool to study and understand the Navier condition. Based on a setup using the photobleaching of fluorescent polymers, I will present our last results on the slip of polymer melts and polymer solutions. 
Wednesday 19 February 2020, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  I will first provide a birdeye view upon the infrared structure of gravity. I will shortly describe the relationship between BMS symmetry, soft theorems and memory effects at leading and subleading orders in the large radius expansion, while emphasizing the specificities of superLorentz symmetries. Secondly, I will present a nogo result on the soft hair conjecture: supertranslations induced by matter creating and falling inside black holes do not affect Hawking radiation, though they do affect scattering amplitudes. I will start by proving that Unruh radiation is unaffected by supertranslations induced by a shockwave and then show that Hawking radiation is mathematically related to this system, as a consequence of the principle of equivalence. Third, I will explain how BMS symmetry is associated to fluxbalance laws that provide constraints upon the motion of binary compact mergers. Finally, I will present the extension of the BMS group to asymptotically de Sitter spacetimes. 
Monday 24 February 2020, 10:30 at
LPTMC,
Jussieu tower 1312 5th floor room 523 ( Minilecture: three times 1.5 hours )  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  TBA 
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. 

[ English version ] 