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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 25 September 2017, 11:00 at 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.

Monday 25 September 2017, 14:00 at 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)

Tuesday 26 September 2017, 14:00 at APC, 483 A - Malevitch APC-TH (Seminar of the theory group of APC) hep-th
Micaela Oertel ( LUTH ) Neutron stars: probing ultra dense (and hot) matter
Abstract: Observed for the first time in 1967 as pulsars, neutron stars represent the most extreme bodies known in nowadays universe. Relict of the gravitational collapse and subsequent supernova explosion of a massive star at the end of its life, they gather a mass of up to twice that of our sun in a sphere with a radius of about 10 km. Their phenomenology is very rich and complex. They are not only very compact, but they are also rotating at frequencies of up to 700 Hz and can have strong magnetic fields of the order $10^{15}$ G. Their modelling requires many different fields of physics such as general relativity, nuclear physics and solid state physics. During this talk, after an introduction, I will discuss some examples of how the confrontation of observational data with neutron star models allows one to probe properties of ultra-dense matter. In the last part of my talk I will present future prospects on how to obtain additional reliable constraints, among others from the observations of binary neutron star mergers with gravitational waves.

Tuesday 26 September 2017, 14:30 at 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.

Tuesday 26 September 2017, 16:30 at 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?
  • AfficheEwineDishoeck.pdf (3350634 bytes) OPEN

Wednesday 27 September 2017, 10:30 at 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.

Wednesday 27 September 2017, 13:00 at 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.

Wednesday 27 September 2017, 14:15 at 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.

Thursday 28 September 2017, 11:00 at 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.

Thursday 28 September 2017, 11:00 at CPHT, Salle de conférences, bât. 6 IPN-X (Séminaire commun de physique théorique des particules IPN-CPHT-X) hep-ph
Rainer Stiele ( Lyon, IPN & Frankfurt U. ) Phase structure and thermodynamics of strongly-interacting matter
Abstract: Currently, large effort is undertaken, experimentally in heavy ion collisions and theoretically doing simulations on supercomputers, to explore the state of matter under the extreme conditions of the largest temperatures and densities in the universe. Effective models, such as Polyakov-loop-extended chiral models, which capture the main properties of the strong interaction, i.e. the creation of constituent quark masses and confinement, play the role of an important guidance that allow access at all temperature and density domains. Results of such a model, the Polyakov-loop-extended Quark-Meson truncation of QCD, for the phase diagram of strongly-interacting matter are presented and it will be discussed how constraints from the high-energy domain (lattice calculations) as well as low energy domain (astrophysics measurements on compact stars) can contribute to pin it down more precisely. The importance of including the quark backreaction on the gauge field dynamics is demonstrated and its impact on the structure of the phase diagram and on the surface tension for nucleation in a first order transition region discussed. Finally, the necessity to improve the description of the gauge part of the strong interaction with phenomenological Polyakov-loop potentials will be motivated and current ways to improve will be outlined.

Thursday 28 September 2017, 14:00 at 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.

Friday 29 September 2017, 14:00 at 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 $Z$.

Monday 2 October 2017, 11:00 at 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)

Monday 2 October 2017, 11:00 at 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.

Tuesday 3 October 2017, 14:00 at APC, 483 A - Malevitch APC-TH (Seminar of the theory group of APC) hep-th
Shinji Mukohyama Solving the flatness problem with an anisotropic instanton in Horava-Lifshitz gravity
Abstract: The first half of this talk reviews the basic construction and some known cosmological implications of a renormalizable theory of gravitation called Horava-Lishitz gravity. In particular, I will explain that (i) the anisotropic scaling with the dynamical critical exponent z=3 renders a field theory of gravity renormalizable, that (ii) the same anisotropic scaling solves the horizon problem and leads to scale-invariant cosmological perturbations even without inflation and that (iii) the infrared instability of the so-called projectable version of the theory can be tamed under a certain condition. We then propose a possible solution to the cosmological flatness problem, in which we assume that the initial condition of the Universe is set by a small instanton respecting the same anisotropic scaling.

Tuesday 3 October 2017, 17:15 at 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

Thursday 5 October 2017, 10:00 at IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Pierre Vanhove ( CEA Saclay ) TBA

Thursday 5 October 2017, 11:00 at 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.

Thursday 5 October 2017, 11:30 at IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Bruno Le Floch ( Princeton ) TBA

Thursday 5 October 2017, 14:00 at 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.

Monday 9 October 2017, 09:00 at IPHT, Amphi Claude Bloch, Bât. 774 SOUTEN-TH (Soutenance de thèse) physics
Thibault Lesieur ( IPhT ) (TBA)

Monday 9 October 2017, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774 IPHT-PHM (Séminaire de physique mathématique) math-ph
Severin Charbonnier ( IPhT ) Large Strebel graphs and $(3,2)$ Liouville CFT
Abstract: 2D quantum gravity is the idea that a set of discretized surfaces (called map, a graph on a surface), equipped with a graph measure, converges in the large size limit (large number of faces) to a conformal field theory (CFT), and in the simplest case to the simplest CFT known as pure gravity, also known as the gravity dressed $(3,2)$ minimal model. \par Planar Strebel graphs are linked to the Strebel foliation of the moduli space of genus 0 Riemann surfaces with n punctures. Restricting this set to graphs which have the same perimeter on every face, makes all computations explicit afterward. We also define the observables to be computed, and their encoding in generating functions. \par I will then define the spectral curve of this model, which --by the means of Topological Recursion-- allows to compute all the observables. It is computable explicitly thanks to the knowledge of intersection numbers of genus 0. \par In the end, by tuning the parameters of the model, we show how to reach a critical point. At this point, the behaviour of observables of large graphs is accessible. We show that at the critical point, the spectral curve is equivalent to the one of the $(3,2)$ minimal model in CFT. This new result is a strong hint that large Strebel graphs shall be equivalent to the the gravity dressed $(3,2)$ minimal model.

Monday 9 October 2017, 11:00 at 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.

Tuesday 10 October 2017, 14:00 at 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

Wednesday 11 October 2017, 10:30 at IHES, Centre de conférences Marilyn et James Simons MATH-IHES (TBA) hep-th
M. Temkin ( The Hebrew University of Jerusalem & IHES ) Logarithmic resolution of singularities
Abstract: The famous Hironaka's theorem asserts that any integral algebraic variety X of characteristic zero can be modified to a smooth variety X_res by a sequence of blowings up. Later it was shown that one can make this compatible with smooth morphisms Y → X in the sense that Y_res → Y is the pullback of X_res → X. In a joint project with D. Abramovich and J. Wlodarczyk, we construct a new algorithm which is compatible with all log smooth morphisms (e.g. covers ramified along exceptional divisors). We expect that this algorithm will naturally extend to an algorithm of resolution of morphisms to log smooth ones. In particular, this should lead to functorial semistable reduction theorems. In my talk I will tell about main ideas of the classical algorithm and will then discuss logarithmic and stack-theoretic modifications we had to make in the new algorithm.

Monday 16 October 2017, 14:30 at IHES, Amphithéâtre Léon Motchane
( Séminaire Géométrie et groupes discrets )
MATH-IHES (TBA) hep-th
Jean-Marc Schlenker ( Université du Luxembourg ) The renormalized volume of quasifuchsian manifolds
Abstract: Quasifuchsian manifolds are an important class of hyperbolic 3-manifolds, classically parametrized by two copies of Teichmüller space. Their volume is infinite, but they have a well-defined finite "renormalized volume" which has nice properties, both analytic and "coarse". In particular, considered as a function over Teichmüller space, the renormalized volume provides a Kähler potential for the Weil-Petersson metric; moreover, it is within bounded additive constants of the volume of the convex core and is bounded from above by the Weil-Petersson distance between the conformal structures at infinity. After describing these properties, we will outline some recent applications (by Kojima, McShane, Brock, Bromberg, Bridgeman, and others) to the Weil-Petersson geometry of Teichmüller space or the geometry of hyperbolic 3-manifolds that fiber over the circle. We will then explain how properties of the renormalized volume suggest new questions and viewpoints on quasifuchsian manifolds. The talk will be accessible to nonexperts.

Monday 16 October 2017, 16:30 at IHES, Amphithéâtre Léon Motchane
( Séminaire Géométrie et groupes discrets )
MATH-IHES (TBA) hep-th
Michelle Bucher ( Unniversité de Genève ) Vanishing simplicial volume for certain affine manifolds
Abstract: Affine manifolds, i.e. manifolds which admit charts given by affine transformations, remain mysterious by the very few explicit examples and their famous open conjectures: the Auslander Conjecture, the Chern Conjecture and the Markus Conjecture. I will discuss an intermediate conjecture, somehow between the Auslander Conjecture and the Chern Conjecture, predicting the vanishing of the simplicial volume of affine manifolds. In a joint work with Chris Connell and Jean-François Lafont, we prove the latter conjecture under some hypothesis, thus providing further evidence for the veracity of the Auslander and Chern Conjectures. To do so, we provide a simple cohomological criterion for aspherical manifolds with normal amenable subgroups in their fundamental group to have vanishing simplicial volume. This answers a special case of a question due to Lück. Joint work with Chris Connell and Jean-François Lafont.

Monday 16 October 2017, 17:15 at 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

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

Thursday 19 October 2017, 10:00 at IHP, 314 RENC-THEO (Rencontres Théoriciennes) hep-th
Niko Jokela ( University of Helsinki ) TBA
Abstract: TBA

seminars from series at institute
in subject with field matching

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