Pantheon SEMPARIS Le serveur des séminaires parisiens Paris

Le serveur de séminaires SEMPARIS accueille toutes les annonces de séminaires de la région parisienne, dans tous les domaines de la physique et des mathématiques. Il vous permet aussi de recevoir par courrier électronique la sélection de votre choix. Enfin, il permet l'archivage des présentations au format PDF ou Powerpoint.   [ Plus d'informations ]

Séminaires à venir [30 suivants]
[ vue agenda ]

Mercredi 20 Septembre 2017, 10:30 à IHES, Centre de conférences Marilyn et James Simons
( Séminaire Mathématique Paris-Tunis )
MATH-IHES (TBA) hep-th
Antoine TouzÉ ( Université Lille 1 ) Structure des foncteurs exponentiels et applications
Abstract: Les foncteurs exponentiels (gradués commutatifs) apparaissent naturellement dans un certain nombre de calculs homologiques (homologie des groupes, des foncteurs...). Dans cet exposé, nous donnerons quelques résultats de structure des foncteurs exponentiels et des applications à des calculs concrets.

Mercredi 20 Septembre 2017, 11:45 à IHES, Centre de conférences Marilyn et James Simons
( Séminaire Mathématique Paris-Tunis )
MATH-IHES (TBA) hep-th
Dorra Bourguiba ( Faculté des Sciences de Tunis ) Complexes associés à une action libre d'un 2-groupe abélien élémentaire sur un CW-complexe fini
Abstract: Soient V=(Z/2Z)n et X un V-CW complexe fini. On construit deux complexes dans la catégorie H*V-U, le premier "algébrique" basé sur la structure de H*V-module de la cohomologie équivariante H*_VX et le second "topologique" utilisant l'action du groupe V sur X. Sous certaines conditions, on montre que ces deux complexes sont acycliques et équivalents.

Jeudi 21 Septembre 2017, 10:00 à IHP, Room 314 RENC-THEO (Rencontres Théoriciennes) hep-th
James Drummond ( Southampton University ) Quantum gravity from conformal field theory
Abstract: I will describe how to recast perturbative quantum gravity using non-perturbative techniques from conformal field theory, focussing on the case of N=4 super Yang-Mills theory. By resolving the degeneracy among double trace operators at large N we are able to bootstrap one-loop supergravity corrections from the OPE of the CFT.

Jeudi 21 Septembre 2017, 11:00 à LPTHE, Bibliothèque SEM-INFOR (Séminaire informel) cond-mat.stat-mech
Olivier Blondeau-Fournier ( Université Laval, Québec ) The KP hierarchy and its superspace construction (2)
Abstract: The Kadomtsev-Petviashvili (KP) hierarchy is a dynamical system that can be viewed as defined on a infinite dimensional Grassmannian and which contains an infinite tower of nonlinear differential equations. This system is completely integrable, meaning that one can find all the conserved quantities, and the various solutions are known exactly. The KP hierarchy interplays with many physical system, such as the related KdV system, and is equivalently formulated as a boson-fermion correspondence. This latter construction is of particular interest since it beautifully connects with the theory of symmetric polynomials, through the formalism of vertex operators and Bernstein operators. In view of its great impact in mathematical physics, the KP hierarchy can be extended to include larger classes of systems with the supersymmetry. In this talk, I will first show a brief review of the KP hierarchy system focusing on its connection with symmetric polynomials and in particular the Schur functions. Then, I will present my recent work on the supersymmetric generalization of the KP hierarchy from the point of view of a superspace analogue of the Bernstein operators.

Jeudi 21 Septembre 2017, 11:45 à IHP, Room 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Miguel Paulos ( LPTENS ) The S-matrix strikes back
Abstract: In this talk I will describe recent work aiming to reinvigorate the 50 year old S-matrix program, which seeks to constrain scattering of massive particles non-perturbatively. I will begin by considering quantum fields in anti-de Sitter space and show that one can extract information about the S-matrix by considering correlators in conformally invariant theories. The latter can be studied with "bootstrap" techniques, which allow us to constrain the S-matrix. I will also show that this can be done directly, without using the CFT crutch, by using crossing symmetry and unitarity and a particular ansatz. In this way we derive universal bounds on QFTs in 2,3 and 4 dimensions.

Jeudi 21 Septembre 2017, 14:30 à IPHT, Amphi Claude Bloch, Bât. 774 SOUTEN-TH (Soutenance de thèse) physics
Lais Sarem-Schunk ( IPhT ) Understanding jet substructure at the LHC
Abstract: Jets are collimated structures emerging from high-energy quarks and gluons. They are ubiquitous in colliders physics, like at the LHC. As we probe higher energies (boosted regimes), new objects are seen as jets. To separate them from quarks and gluons, it is necessary to access the internal dynamics of jets, that is to explore their substructure. These methods are used in a variety of measurements and searches at the LHC. In my PhD thesis I study jet substructure techniques at the LHC, focusing on the identification of two-pronged jets like boosted W/Z/H bosons. I adopt an analytical approach based on all-order resummation techniques in perturbative QCD. I will present studies of different methods and use the insight from these calculations to propose new variants and tools that have a better separation performance and are more resilient to model-dependent non-perturbative effects.

Jeudi 21 Septembre 2017, 16:00 à LPT, 114 LPT-PTH (Particle Theory Seminar of LPT Orsay) hep-ph
Rajan Gupta ( Los Alamos National Laboratory ) Nucleon structure and nEDM from lattice QCD
Abstract: This talk will summarize the calculation of matrix elements of various bilinear quark operators within nucleon states being done at LANL to extract isovector charges and form factors. I will then describe the calculation of matrix elements of novel CP violating operators that contribute to the neutron EDM.

Lundi 25 Septembre 2017, 11:00 à IAP, Salle des séminaires SEM-GRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP) astro-ph
Christian Marinoni ( CPT Marseille ) `E pur si muove’ A real-time detection of our motion through space.
Abstract: High-precision astrometric experiments will allow to detect our proper acceleration through space via real-time observations of the change in the aberration of sources at cosmic distances. This Aberration Drift effect is a powerful consistency test of FLRW metrics, it may set independent constraints on the amplitude of the Hubble constant and the linear growth rate of cosmic structures, and it may also be instrumental in searching for evidences of new physics beyond the standard model. I will present the mechanics of this novel test of cosmology, discuss the physics to which it is sensitive and show simulated forecasts of the accuracy with which it can be implemented by ongoing satellite missions such as Gaia or upgraded future experiments.

Lundi 25 Septembre 2017, 14:00 à IPHT, Salle Claude Itzykson, Bât. 774 IPHT-STA (Séminaire de Physique Statistique, CEA/Saclay) cond-mat
Nicholas Sedlmayr ( Institute of Mathematical and Theoretical Physics, Michigan State University ) The Superconductivity of Topologically Protected Surface States
Abstract: The superconducting proximity effect induced in materials in close contact with a superconductor is well known. Similarly the topologically protected surface states recently found on the surfaces of special crystals can leak into appropriate adjoining materials. We bring these two effects into proximity and study how superconductivity and topologically protected surface states interact with each other, a situation of interest in the search for Majorana bound states. We look at the scanning tunneling microscopy of a large topological insulator with superconducting islands deposited on the surface, and analyze theoretical models which capture the hybridization between the topological surface states and the superconducting states. The density of states of both the topological insulator and the superconductor turn out to exhibit interesting proximity effects and open up new possibilities for observing Majoranas. \\ \\ (Organizer: Cristina Bena)

Mardi 26 Septembre 2017, 14:00 à APC, 483 A - Malevitch APC-TH (Seminar of the theory group of APC) hep-th
Micaela Oertel ( LUTH ) TBA

Mardi 26 Septembre 2017, 14:30 à IHES, Amphithéâtre Léon Motchane PT-IHES (Séminaire de physique théorique de l'IHES) hep-th
Carlangelo Liverani ( Universita' di Roma Tor Vergata & IHES ) The Lorentz Gas : New Results and Open Problems
Abstract: I will make a quick review of old and new results concerning the Lorentz gas; discuss new directions in which I’d like to proceed (e.g. non periodic obstacles, interacting particles, …) and some (very) partial results toward such directions.

Mardi 26 Septembre 2017, 16:30 à UPMC, Amphithéâtre Charpak CPMC (Colloquium Pierre et Marie Curie) astro-ph
Ewine Van Dishoeck ( Leiden Observatory ) Building stars, planets and the ingredients for life in space
Abstract: One of the most exciting developments in astronomy is the discovery of thousands of planets around stars other than our Sun. But how do these exo-planets form, and why are they so different from those in our own solar system? Which ingredients are available to build them? Thanks to powerful new telescopes, especially the Herschel Space Observatory and the Atacama Large Millimeter Array (ALMA), astronomers are starting to address these age-old questions scientifically. Stars and planets are born in the cold and tenuous clouds between the stars in the Milky Way, and ALMA allows us to zoom in on planetary construction zones for the first time. Water and a surprisingly rich variety of organic materials are found, including simple sugars. Can these pre-biotic molecules end up on new planets and form the basis for life elsewhere in the universe?
Fichiers attachés:
  • AfficheEwineDishoeck.pdf (3350634 bytes) OPEN

Mercredi 27 Septembre 2017, 10:30 à IHES, Centre de conférences Marilyn et James Simons
( Séminaire de Géométrie Arithmétique Paris-Pékin-Tokyo )
MATH-IHES (TBA) hep-th
T. Kato ( University of Chicago ) Toroidal compactifications of moduli spaces of Drinfeld modules
Abstract: For the moduli space of Drinfeld modules, the compatification of Satake-Baily-Borel type was constructed by Kapranov in a special case and by Pink in general. The toroidal compactification was studied by Pink and Fujiwara in early 1990's and Pink wrote a short summary. However details were not yet published. Fukaya, Sharifi and I are completing a joint paper which describes the constructions of toroidal compactifications in detail. I will explain it. Polyhedral enlargements of Bruhat-Tits buildings play important roles there.

Mercredi 27 Septembre 2017, 13:00 à LPT, Amphi 1, bat 210, 2eme etage, LPT-Orsay SOUTEN-TH (Soutenance de thèse) hep-ph
Olcyr Sumensari ( LPT Orsay ) Search of new physics through flavor observables/Recherche de la nouvelle physique a travers les observables de la physique de la saveur
Abstract: Indirect searches of physics beyond the Standard Model through flavor physics processes at low energies are complementary to the ongoing efforts at the LHC to observe the New Physic phenomena directly. In this thesis we discuss several scenarios of physics beyond the Standard Model by (a) reusing the effective field theory approach and (b) by considering explicit extensions of the Standard Model, namely the two-Higgs doublet models and the scenarios involving the low energy scalar leptoquark states. Particular emphasis is devoted to the issue of the lepton flavor universality violation in the exclusive decays based on $b \to s\ell\ell$ et $b\to c\tau\nu$, and to the possibility of searching for signs of lepton flavor violation through similar decay modes. A proposal for testing the presence of the light CP-odd Higgs through quarkonia decays is also made. La recherche indirecte des effets de la physique au-delà du Modèle Standard à travers les processus de la saveur est complémentaire des efforts au LHC pour observer directement la nouvelle physique. Dans cette thèse, nous discutons plusieurs scénarios au-delà du Modèle Standard (a) en utilisant une approche basée sur les théories de champs effectives et (b) en considérant des extensions explicites du Modèle Standard, à savoir les modèles à deux doublets de Higgs et les scénarios postulant l’existence des bosons leptoquarks scalaires à basse énergie. En particulier, nous discutons le phénomène de la brisure de l'universalité des couplages leptoniques dans les désintégrations basées sur les transitions $b \to s\ell\ell$ et $b\to c\tau\nu$, et la possibilité de chercher les signatures de la violation de la saveur leptonique à travers les modes de désintégration similaires. Une proposition pour tester la présence d'un boson pseudo-scalaire léger à travers les désintégrations des quarkonia est aussi présentée.

Mercredi 27 Septembre 2017, 14:15 à IPHT, Salle Claude Itzykson, Bât. 774 IPHT-MAT (Séminaire de matrices, cordes et géométries aléatoires) hep-th
Susha Parameswaran ( University of Liverpool ) Anti-D3 branes and moduli in non-linear supergravity
Abstract: With a view towards string cosmology and de Sitter vacua, I will consider a probe anti-D3 brane in a supersymmetric flux compactification with non-perturbative effects. Postponing questions of backreaction, singularities and tachyons, the anti-D3 brane spontaneously breaks supersymmetry and the effective field theory describing the system at low energies is a supergravity theory with non-linearly realised supersymmetry. \par Guided by string theory modular symmetry, I will show how to compute this non-linear supergravity theory, including dependence on all bulk moduli. Using either a constrained chiral superfield or a constrained vector field, the uplifting contribution to the scalar potential from the anti-D3 brane can be parameterised either as an F-term or Fayet-Iliopoulos D-term. Using again the modular symmetry, we show that 4D non-linear supergravities that descend from string theory have an enhanced protection from quantum corrections by non-renormalisation theorems. The superpotential giving rise to metastable de Sitter vacua is robust against perturbative string-loop and $\alpha ^\prime$ corrections.

Jeudi 28 Septembre 2017, 11:00 à LPTHE, Bibliothèque SEM-INFOR (Séminaire informel) cond-mat.stat-mech
Camille Aron ( LPTENS ) (Non) equilibrium dynamics: a (broken) symmetry
Abstract: It is fascinating that most many-body systems, if unperturbed, tend to relax towards thermal equilibrium. I will discuss a recent result showing that quantum equilibrium dynamics can be elevated to the rank of a universal (model-independent) symmetry of Keldysh field theories. This fundamental symmetry imposes strong constraints on the equilibrium correlation functions. But more importantly, this allows to study non-equilibrium dynamics as symmetry-breaking processes, providing important clues on the so-far poorly understood production of entropy in quantum mechanical systems.

Jeudi 28 Septembre 2017, 14:00 à LPT, amphi 1, bat 210, 2eme etage SOUTEN-TH (Soutenance de thèse) hep-ph
Mattias Rodriguez ( LPT Orsay, LAPTH Annecy ) La recherche de bosons de Higgs supplémentaires au LHC/Search for supplementary Higgs bosons at the LHC
Abstract: Despite its incontestable experimental success, the Standard Model of particle physics leaves unanswered many fundamental questions like the hierarchy problem and the origin of dark matter, motivating the study of physics beyond its scope. The NMSSM is a well-motivated extension of the SM addressing these two issues. It features a rich phenomenology accessible, in principle, at the LHC. In particular, the Higgs sector of the NMSSM is extended with respect to the SM giving rise to six scalars. It is the aim of this thesis to study the discovery potential of these extra Higgs bosons at the LHC. After introducing the NMSSM and its motivation, we first study the discovery prospects for a scalar lighter than the 125 GeV resonance found at CERN, reviewing its possible production and detection at the upcoming runs of the LHC and its possible impact on couplings of the Standard Model Higgs boson. Next, prospects for searches via Higgs cascades involving extra light and heavy Higgs bosons are presented. Detailed studies by means of Monte Carlo methods are performed, and new dedicated analysis are proposed. These last results are not confined to the NMSSM and can be interpreted in a wide class of models. Malgr´e un succ`es exp´erimental incontestable, le Mod`ele standard (MS) de la physique des particules laisse de nombreuses questions fondamentales sans r´eponse, comme le probl`eme de hi´erarchie et l’origine de la mati`ere noire, motivant l’´etude de la “ nouvelle physique”. Le Next-to- Minimal Supersymmetric Standard Model (NMSSM) est une extension tr`es int´eressante du MS r´epondant `a ces deux probl`emes. Il comprend une riche ph´enom´enologie, en principe accessible au Grand Collisionneur de Hadrons (LHC). En particulier, son secteur de Higgs est ´etendu par rapport au MS, g´en´erant six scalaires. Le but de cette th`ese est d’´etudier le potentiel de d´ecouverte de ces bosons de Higgs suppl´ementaires au LHC. Apr`es une introduction du NMSSM et de ses motivations, nous ´etudions d’abord les perspectives de d´ecouverte d’un scalaire, plus l´eger que la r´esonance `a 125 GeV mise en ´evidence au CERN, en passant en revue ses possibles modes de production et de d´etection dans les phases `a venir du LHC, et ses possibles impacts sur les couplages du boson de Higgs du MS. Ensuite, les perspectives de recherche via les cascades de Higgs, impliquant des bosons de Higgs suppl´ementaires l´egers et lourds, est pr´esent´ee. Des ´etudes d´etaill´ees au moyen de m´ethodes Monte-Carlo ont ´et´e r´ealis´ees, et de nouvelles analyses d´edi´ees sont pr´esent´ees. Ces derniers r´esultats ne sont pas restreints au NMSSM, et peuvent ˆetre interpr´et´es dans une large classe de mod`eles.

Vendredi 29 Septembre 2017, 14:00 à LPT, Amphi 1, bat 210, 2eme etage, LPT SOUTEN-TH (Soutenance de thèse) hep-ph
Andrei Angelescu ( LPT Orsay ) Scalars in (Warped) Extra Dimensions: Climbing from the Bottom to the Top
Abstract: Almost two decades ago, the paradigm of extra-dimensional models addressing the gauge hierarchy problem attracted much attention through the elegant proposals of large, flat extra dimensions (EDs) -- the Arkani-Hamed-Dimopoulos-Dvali or ADD model -- and warped EDs -- the Randall-Sundrum or RS model. In this thesis, we discuss several models inspired from such extra-dimensional scenarios. We start by introducing some key elements of field theory in five space-time dimensions and showing how such scenarios provide a solution to the hierarchy problem. Afterwards, in a first part of this work, we adopt a bottom-up approach and study several models containing Vector-Like Fermions (VLFs), which are typically predicted in ED frameworks. We show how adding Vector-Like Quarks (VLQs) to the Standard Model (SM) allows one to simultaneously explain the anomalies in the (i) $b$-quark forward-backward asymmetry ($A_{\rm FB}^b$) measured at the Large Electron-Positron collider (LEP) and (ii) the $t\bar{t} h$ production cross section measured at the Large Hadron Collider (LHC). Using the so-called Higgs decay ratios, we also estimate the sensitivity of the upgraded LHC, the High-Luminosity LHC, to the presence of VLQs. Then, we consider a Two-Higgs Doublet Model (2HDM) extended with Vector-Like Leptons (VLLs) in order to fit the mysterious 750~GeV excess observed at LHC in late 2015. Within a similar model, we also explain the Dark Matter (DM) abundance in the Universe, our DM candidate being a neutral VLL, which is rendered stable by a suitable $\mathbb{Z}_2$ symmetry. Later on, in a second part of the thesis, we focus on the more concrete warped ED scenario endowed with a bulk custodial symmetry, which protects the model from large electroweak (EW) corrections. In this framework, we first interpret the 2~TeV diboson bump observed at LHC in 2015 as a superposition of Kaluza-Klein (KK) gauge bosons produced in the $s$-channel. Afterwards, we study the phenomenology of the mixed Higgs-radion scalar sector of the aforementioned model. In particular, we estimate the sensitivity of the LHC and of a future electron-positron collider (the International Linear Collider - ILC) to the existence of a radion via its production in association with a $Z$ boson. Il y a près de deux décennies, l'utilisation des modèles à dimensions supplémentaires pour résoudre le problème de hiérarchie des théories de jauge a reçu beaucoup d'attention, gr\^{a}ce \`{a} d'élégantes propositions: des dimensions supplémentaires (DS) étendues et plates -- le modèle d'Arkani-Hamed-Dimopoulos-Dvali, ou ADD -- ainsi que des DS courbées -- le modèle de Randall-Sundrum, ou RS. Dans cette thèse, nous discutons plusieurs modèles inspirés de tels scénarios de dimension sup\`{e}rieure. Pour commencer, nous introduisons des éléments-clés de la théorie des champs en cinq dimensions, et nous montrons comment de tels scénarios apportent une réponse au problème de hiérarchie. Ensuite, dans une première partie, nous adoptons une approche ``de bas en haut'' et étudions plusieurs modèles contenant des fermions vectoriels (FV), prédits génériquement dans les modèles de DS. Nous montrons qu'en ajoutant des quarks vectoriels (QV) au Modèle Standard (MS), on peut expliquer en même temps les anomalies (i) d'asymétrie avant-arrière des quarks $b$ ($A^b_{\rm FB}$) mesurée au Large Electron-Positron collider (LEP) et (ii) de section efficace de production de $t\bar{t} h$ mesurée au Large Hadron Collider (LHC). En utilisant des rapports de taux de désintégration du Higgs, nous estimons aussi la sensibilité du LHC amélioré, le LHC à haute luminosité, à la présence de QV. Puis nous considérons un modèle à deux doublets de Higgs (2HDM), accompagné de leptons vectoriels (LV) pour expliquer le mystérieux excès à 750 GeV observé au LHC fin 2015. Dans un modèle similaire, nous expliquons également l'abondance de matière noire (MN) dans l'Univers, notre candidat pour la MN étant un LV neutre, stabilisé par une symétrie $\mathbb{Z}_2$ appropriée. Dans une deuxième partie de la thèse, nous nous penchons sur le scénario plus concret des DS courbées dotées d'une symétrie custodiale dans l'espace \`{a} cinq dimensions, qui protège le modèle vis-à-vis de larges corrections aux observables de précision électrofaibles. Dans ce cadre, nous interprétons tout d'abord la r\'{e}sonance à deux bosons observée à 2 TeV au LHC comme \'{e}tant une superposition de bosons de jauge de Kaluza-Klein, produits dans le canal $s$. Dans un deuxième temps, nous étudions la phénoménologie du secteur scalaire du modèle susdit, qui m\'{e}lange le boson de Higgs et le radion. En particulier, nous estimons la sensibilité du LHC et d'un futur collisionneur électron-positron (l'International Linear Collider - ILC) à la pr\'{e}sence d'un radion, via la production de celui-ci en association avec un boson $Z$.

Lundi 2 Octobre 2017, 11:00 à IPHT, Salle Claude Itzykson, Bât. 774 IPHT-STA (Séminaire de Physique Statistique, CEA/Saclay) cond-mat
Aurélien Decelle ( Lab. de Recherche en Informatique, Univ. Paris Sud, Orsay ) (TBA)

Lundi 2 Octobre 2017, 11:00 à IAP, Salle des séminaires SEM-GRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP) hep-th
Sebastian Garcia-Saenz ( IAP ) Phonons in holographic superfluids and solids
Abstract: After reviewing the gravitational dual of superfluids in the context of AdS/CFT, I will describe an analytical method to derive the low-energy spectrum of the boundary theory. The result confirms that, at zero temperature, the effective theory consists of a longitudinal phonon with the correct speed of sound. I will next move on to consider the EFT of solids and use it to motivate the construction of a holographic dual. Here too we are able to derive the correct low- energy effective theory of the phonons in a conformally invariant solid. Lastly we obtain some numerical solutions including backreaction and calculate the free energy, finding evidence that the system “melts” into a black hole as the temperature is raised, which we interpret as a solid- to-liquid phase transition on the field theory side.

Mardi 3 Octobre 2017, 17:15 à DPT-PHYS-ENS, Salle Jean Jaurès (29 rue d'Ulm) SEM-PHYS-ENS (Colloquium du Département de Physique de l'ENS) quant-ph
Michel Brune ( LKB ) Prix des Trois Physiciens

Jeudi 5 Octobre 2017, 10:00 à IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Pierre Vanhove ( CEA Saclay ) TBA

Jeudi 5 Octobre 2017, 11:00 à LPTHE, Bibliothèque SEM-LPTHE (Séminaire du LPTHE) cond-mat.stat-mech|hep-th|math-ph
Jean-Bernard Zuber ( LPTHE ) Horn's problem, from classical to quantum
Abstract: Horn's (classical) problem deals with the following question: what can be said about the spectrum of eigenvalues of the sum C=A+B of two Hermitian matrices of given spectrum ? Curiously this problem is intimately related to the "quantum" problem : given two irreducible representations of SU(n), which irreps appear in their tensor product ? The support of the spectrum of C is well understood, after a long series of works from Weyl (1912) to Knutson and Tao (1999), and the classical problem is known to provide an asymptotic approach of the quantum one. Here I show how an explicit computation based on a well-known matrix integral enables one to determine the probability distribution of the eigenvalues of C, and sheds some new light on the relation between the classical and quantum problems.

Jeudi 5 Octobre 2017, 11:30 à IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Bruno Le Floch ( Princeton ) TBA

Jeudi 5 Octobre 2017, 14:00 à LPTM, 4.13 St Martin II SEM-LPTM-UCP (Seminaires du LPTM , Universite de Cergy Pontoise) cond-mat
Andreas Honecker ( LPTM UCP Cergy Pontoise ) The magnetocaloric effect: history and perspectives
Abstract: The magnetocaloric effect, i.e., the change of temperature induced by an adi- abatic change of an external magnetic field was discovered by Warburg in 1881 during his investigations of iron. Subsequently, back in 1933, cooling by adia- batic demagnetization of paramagnetic salts was the first method to reach tem- peratures below 1 K. Until today, adiabatic demagnetization remains the method of choice to cool solids to the milli-Kelvin range or below. In addition, cooling by adiabatic demagnetization at intermediate temperatures (Kelvin-range) is un- der discussion for space applications and future linear colliders. Such applica- tions would benefit from more efficient materials. On this background, we re- view recent ideas how to go beyond single-ion systems, and exploit interactions between magnetic moments of dipolar or Heisenberg nature to enhance mag- netocaloric properties. Specifically, we discuss the enhanced magnetocaloric effect observed in geometrically frustrated magnets and close to field-induced quantum phase transitions.

Lundi 9 Octobre 2017, 09:00 à IPHT, Salle Claude Itzykson, Bât. 774 SOUTEN-TH (Soutenance de thèse) physics
Thibault Lesieur ( IPhT ) (TBA)

Lundi 9 Octobre 2017, 11:00 à IAP, Salle des séminaires SEM-GRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP) hep-th
David Andriot ( CERN ) Classical de Sitter string backgrounds
Abstract: Realising cosmological models in string theory, by for instance embedding inflation models in a string compactification, typically requires to have a metastable de Sitter background. The latter would correspond to e.g. the vacuum at the end of inflation. Here we focus on classical backgrounds: those only contain well-controlled ingredients to realise the embedding as a compactification. Such de Sitter solutions are very difficult to obtain, and there exists so far no metastable example. We study this problem and as a first step, we derive new constraints on the existence of classical de Sitter solutions, considering various configurations of D-branes and orientifolds. While some configurations completely forbid having de Sitter solutions, others still allow for it in small regions of the parameter space that we identify.

Mardi 10 Octobre 2017, 14:00 à APC, 483 A - Malevitch83 A - Malevitch APC-TH (Seminar of the theory group of APC) hep-th
Nicolás Wschebor ( Universidad de la República, Montevideo ) Naturally light scalars

Lundi 16 Octobre 2017, 17:15 à DPT-PHYS-ENS, TBA
( ¡¡ Please be aware of the unusual day: Monday !! )
SEM-PHYS-ENS (Colloquium du Département de Physique de l'ENS) physics.chem-ph
Jean-Pierre Sauvage ( Université de Strasbourg ) TBA

Mardi 17 Octobre 2017, 14:00 à APC, 483 A - Malevitch APC-TH (Seminar of the theory group of APC) hep-th
Eugeny Babichev ( LTP Orsay ) TBA

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