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Theorique d'Orsay

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Agenda > Séminaires / Seminars > Particules Dernier ajout : jeudi 2 octobre 2014.

Séminaires Particules 2009-2010

Les séminaires se tiennent en salle 114 au 1er étage du bâtiment 210, généralement le jeudi à 16h, sauf indication contraire.

Contact pour les séminaires : Benoît Blossier.


-  Jeudi 29 Juillet 2010 à 16h, salle 114

Pablo Roig (LPT Orsay) : A precise determination of the eta_c mass and width from radiative J/Psi decays seminaireroig10bis, PDF - 1.7 Mo

Motivated by two recent analysis by the CLEO and KEDR collaborations of the eta_C line shape in radiative J/Psi decays, we have studied the problem within an EFT approach provided by potential-NRQCD (pNRQCD) that exploits : the non-relativistic nature of the problem, the weak-coupling regime where these states lie and the multiple expansion in the photon energy in a consistent framework. Relativistic corrections to the lowest order result are also included. We compare our results for the eta_c mass and width to those found by CLEO and KEDR and comment on the related uncertainties and issues.


-  Mercredi 21 Juillet 2010 à 16h, salle 114

Igor Bogolubsky (JINR Dubna) : Towards the continuum limit of the lattice Landau-gauge gluon and ghost propagators seminairebogo2010, PDF - 378.6 ko

Considerable efforts have been devoted during the last decade to exploring QCD’s elementary two-point functions using the framework of lattice QCD. Thereby, much attention has been paid to the gluon and ghost propagators in Landau gauge whose low-momentum behavior has been explored using relatively coarse lattices to reach momenta as low as possible. To ultimately confront such lattice results with corresponding predictions from continuum functional theory, the extrapolation to the continuum limit has to be under control, however. Also, the influence of the Gribov ambiguity needs to be understood, in particular as there are strong indications that this ambiguity has a big impact on these propagators at low momenta.

To further clarify this still actively debated issue we have launched a large scale lattice study of this problem in SU(2) gluodynamics, paying special attention to the continuum limit of the gluon and ghost propagators and the associated coupling at a fixed physical volume.


-  Jeudi 3 Juin 2010 à 11h, salle 114 (HORAIRE INHABITUEL)

Julien Serreau (APC) : 2PI functional techniques for gauge theories PDF - 4.1 Mo

Two-particle-irreducible (2PI) techniques provide a powerful resummation tool in quantum field theory, of interest for the description of quantum fields at high temperature, or of far-from-equilibrium dynamics. We discuss the formulation of 2PI techniques for gauge theories, with particular emphasis on the key issues of symmetries and renormalization.


-  Mardi 1er Juin 2010 à 16h, salle 114

Nils Offen (Université de Regensburg) : On one-loop renormalization of heavy-light light-ray operators

In light-cone gauge the renormalization at one loop of light-ray operators is governed by 2-particle kernels. Based on work done by Bukhvostov, Frolov, Lipatov, Kuraev and Braun, Manashow, Rohrwild in the light-light case this property is used to generalize known results for the one-loop renormalization of heavy-light operators. Comparing to results for light-light operators, we tentatively point out similarities and take first steps towards an understanding of the mixing pattern of different heavy-light light-ray operators.


-  Jeudi 27 Mai 2010 à 16h, salle 114

Slava Rychkov (LPT ENS et Université Paris VI) : Gravitational scattering at transplanckian energies

Suppose that a TeV-scale gravity scenario, like in Large Extra Dimensions, is realized in Nature, so that LHC protons will collide at CM energies exceeding the Planck scale. What shall we see ? In this talk we will discuss the common lore and continuing theoretical work trying to clarify this question.


-  Jeudi 20 Mai 2010 à 16h, salle 114

Mauro Anselmino (Universite de Turin) : Spin effects at high energy and the nucleon structure

Several surprising spin effects have been and keep being observed and measured in the last years in several inclusive processes at high energies. Their interpretation and description can be related to the intrinsic motion of quarks, thus leading to a possible 3-dimensional exploration of the partonic structure of protons and neutrons.


-  Jeudi 29 Avril 2010 à 16h, salle 114

Dru Renner (DESY) : Hadronic contribution to g-2 from lattice QCD

The hadronic contributions to the anomalous magnetic moment of the muon are an interesting challenge for lattice QCD calculations, especially given a persistent discrepancy between theory and experiment. We have calculated the leading order hadronic contribution for pion masses from 600 MeV to 270 MeV using dynamical twisted mass fermions. This observable receives a significant contribution from two pion states, in particular the rho resonance. Time permitting, I’ll show some results from our current efforts to analyze pion-pion scattering on the lattice.


-  Jeudi 22 Avril 2010 à 16h, salle 114

Pasquale di Bari (Université de Southampton) : N_2-dominated leptogenesis

In my talk I will discuss a scenario of minimal leptogenesis (thermal + type I seesaw mechanism) that is interesting because potentially testable just at future low energy neutrino experiments. In the last years it become clear that a reliable calculation of the final asymmetry in leptogenesis has in general to take into account the contribution produced from the heavier RH neutrino decays. In particular the contribution from the next-to-lightest RH neutrinos (the "N_2" neutrinos) decays can be the dominant source when the RH neutrino mass spectrum exhibits a strong hierarchy and the lightest RH neutrino N_1 is sufficiently light to give a negligible contribution to the final asymmetry. Interestingly, this scenario can be motivated within grand unified theories. In this case further restrictions can be imposed on the seesaw parameters such that the final asymmetry can be expressed just in terms of the low energy parameters. Furthermore, imposing successful leptogenesis could potentially yield predictions on the low energy neutrino parameters. I will show how recently studied effects, flavour coupling and so called phantom terms, can remarkably influence the final result and have therefore to be taken into account.


-  Jeudi 15 Avril 2010 à 16h, salle 114

Kirill Semenov (LPT et CPHT Ecole Polytechnique) : Pion-nucleon transition distribution amplitudes : conformal PW expansion v.s. spectral representation seminairesemenov2010, PDF - 2.4 Mo

Pion-nucleon transition distribution amplitudes are the recently proposed non-perturbative objects which arise e.g. in the description of exclusive production of baryons off nucleons on the base of QCD factorization. I am going to discuss the possible approaches to the problem of suggesting of phenomenological parametrizations for pion-nucleon TDAs.


-  Jeudi 8 Avril 2010 à 16h, salle 114

Domenec Espriu (CERN et Université de Barcelone) : Using high energy cosmic rays to detect the axion halo

We investigate the propagation of a charged particle in a spatially constant, but time dependent, pseudoscalar background. Physically this pseudoscalar background could be provided by a relic axion density. The background leads to an explicit breaking of Lorentz invariance ; as a consequence the process p-> p gamma is possible and the background acts as a shield against extremely energetic cosmic rays, an effect somewhat similar to the GZK cut-off effect. The effect is model independent and can be computed exactly. The hypothetical detection of the photons radiated via this mechanism would provide an indirect way of verifying the cosmological relevance of axions.


-  Mardi 6 Avril 2010 à 16h30, salle 114

Javier Virto (Université de Rome) : Flavor Physics in the MSSM seminairevirto2010, PDF - 11.6 Mo

Flavor changing processes involving mesons have been used for over 15 years to constrain the soft SUSY breaking sector of the MSSM. The fact that the flavor structure of this sector is highly non-generic is called the SUSY flavor problem. Most of the phenomenological analyses on the general MSSM have therefore assumed that the spectrum is almost aligned or degenerate. I will review the calculation of the effective low energy theory for quark flavor changing processes in the MSSM, and the related phenomenology, going beyond the degenerate squark approximation.


-  Vendredi 26 Mars 2010 à 15h30, Amphi 1

Swarup Kumar Majee (Université de Louvain) : Neutrino mass and leptogenesis in a SUSY SO(10) model

The smallness of the neutrino mass can be explained by different type of seesaw mechanism. Type-I seesaw is realised with a heavy right handed Majorana neutrino, natrual element in SO(10) GUT model, which can also generate the observed lepton asymmetry through it’s decay. On the other hand low scale supersymmetry not only helps to explain the wide disparity between the weak and GUT scales but also leads to a unification of gauge couplings at high energies. The mass scale of this right-handed neutrino, thus, constrained by several aspects of physics. In our work, introducing an SO(10) singlet lepton, we find a novel way to accommodate the observed neutrino masses and mixings as well as generate the desired lepton asymmetry.


-  Jeudi 18 Mars 2010 à 16h30, salle 114

Alessio Notari (CERN et Université de Heidelberg) : Inflation from Phase Transitions in Scalar-Tensor theories and an Approach to the Hierarchy Problem

Inflation with tunneling from a false to a true vacuum is viable in the presence of a non-minimally coupled scalar field. This has precise interesting predictions on cosmological scalar and tensor fluctuations in the CMB. Moreover we predict a spectrum of gravity waves produced at reheating with large amplitude. As a by-product the additional field also sets dynamically the value of the Planck mass, which can be exponentially large. Therefore along with Inflation we also suggest a dynamical explanation for why gravity is so weak today. In this case the spectrum of gravity waves is peaked at 0.1 mHz and thus detectable by the planned space inteferometer LISA. Finally we discuss possible ways of making the additional scalar compatible with late-time constraints.


-  Mardi 16 Mars 2010 à 16h30, salle 114

David Greynat (Université de Barcelone) : Mellin-Barnes representation and calculations in Quantum Field Theory

In a first part of my talk, I will show how the Mellin-Barnes representation of Feynman diagrams with one scale (i.e. one ratio of masses and/or momenta), when combined with the converse mapping theorem, allows the simplification of the analytic evaluation, to an arbitrary order, of their asymptotic expansions in powers and logs of this scale. In a second part, I will extend this method to Feynman diagrams containing several scales. For this, we will use multidimensional complex analysis and especially multidimensional residues theory. This very general technique can be applied to different domains. I will illustrate it by evaluating analytically a specific class of 5-loop QED contributions to the anomalous magnetic moment of the muon, involving the masses of the electron, muon and tau and some other integrals involved in the calculation of the hadronic contributions to the g-2. At last, in a third part, I will show that the Mellin-Barnes representation may also deal with non-perturbative effects, although its kernel is of perturbative type. Mixing Mellin-Barnes representation, inverse factorial expansions and Borel resummation, we will see that it is possible to rewrite, in terms of non-perturbative series, the tail of the (divergent) formal power series which constitutes the perturbative expansion of an arbitrary N-point function for the simple case of zero-dimensional $phi^4$ field theory. The perturbative results will then give birth to hyperasymptotic expansions.


-  Vendredi 12 Mars 2010 à 16h30, salle 114

Duc Ninh LE (Max Planck Institute) : Electroweak radiative corrections at colliders. seminaireninhle2010, PDF - 1.2 Mo

In this talk I will discuss the electroweak radiative corrections to WWZ and ZZZ production at the linear collider, and also bbH production at the LHC. In so doing I will explain in some detail how to do an one-loop multi-leg calculation. The topic of Landau singularity and its phenomenological consequences in bbH production at the LHC will also be considered.


-  Jeudi 11 Mars 2010 à 16h30, salle 114

Emilie Passemar (Université de Valence) : Study of eta —> 3 pi decays with a dispersive approach seminairepassemar2010, PDF - 970.9 ko

Recently, an important effort has been devoted at KLOE, MAMI and COSY to precisely measure the eta —> 3 pi decays. These new measurements require to revisit the theoretical analyses of these decays. In this talk, we will present a new analysis of the eta —> 3 pi decay amplitude relying on dispersive methods. Using analyticity and unitarity, the amplitude is determined up to subtraction constants which are then fixed by a combined matching to the experimental measurements and to the calculations of chiral perturbation theory. This approach is particularly interesting, since it allows to take into account the pi pi rescattering effects, which are known to be significant in this channel. We will show how the study of this decay allows to extract a fundamental parameter of the Standard Model, namely the quark mass ratio (m_d^2-m_u^2)/(m_s^2-\hatm^2) with a good precision.


-  Jeudi 4 Mars 2010 à 16h30, salle 114

Giovanni Chirilli (LPT et CPHT Ecole Polytechnique) : High-Energy Amplitudes in Gauge Theories at next to leading order seminairechirilli2010, PDF - 4.4 Mo

At high-energy (Regge limit) the T product of two currents can be expanded in terms of coefficient functions (impact factors) and matrix elements of "composite color dipoles" made of Wilson line operators with rapidity cutoff preserving conformal invariance. The behavior of the amplitude in gauge theories can then be reformulated in terms of Wilson-line operators, and the evolution at leading order is governed by the non-linear Balitsky-Kovchegov (BK) equation. In order to see if the BK equation is relevant for existing or future deep inelastic scattering (DIS) accelerators (like Electron Ion Collider or Large Hadron electron Collider) one needs to know the NLO corections. In addition, the NLO corrections define the scale of the running-coupling constant in the BK equation and therefore determine the magnitude of the leading-order cross section. Using the high-energy OPE, we find the next-to-leading order (NLO) correction to the BK equation and calculate the impact factor for virtual photons in deep inelastic scattering.


-  Mardi 2 Mars 2010 à 16h30, salle 114

Jean-Philippe Lansberg (CPHT Ecole Polytechnique) : Looking at hadrons in the backward direction with hard photons : the Transition Distribution Amplitudes seminairelansberg2010, PDF - 1.3 Mo

I will discuss the potentialities offered by the study of backward exclusive processes in the scaling regime, such as backward DVCS, backward electroproduction of a meson. I shall first introduce the concept of Transition Distribution Amplitudes (TDAs) by underlining some similarities and differences compared to Generalised Parton Distributions (GPDs). As a first illustration, I will discuss the simple case of gamma* gamma -> rho pi at small t, for which we can extend models used for GPDs. I will discuss also the possibility to study DVCS on a virtual-pion target. Finally, I shall focus on the baryonic transitions such as p -> pi, which appear in backward electroproduction of a meson at JLab and Compass as well as in the production of a hard dilepton with a pion in exclusive antiproton-proton annihilations at GSI. In the latter case, I will discuss our first estimate of some cross sections that will be measured soon and our plans to study the heavy quark content in the proton.


-  Jeudi 25 Février 2010 à 16h30, salle 114

Stefano Actis (Paul Scherrer Institut) : NLO electroweak corrections to Higgs production in gluon-gluon fusion seminaireactis2010, PDF - 553.3 ko

The production of the Higgs boson via gluon fusion is a key processes at the LHC and several classes of higher order corrections have been computed in the last few years. In this seminar I will focus on the evaluation of the two-loop electroweak corrections in the context of the Standard Model, comparing results obtained through different schemes for dealing with unstable particles and showing the numerical relevance for collider physics.


-  Jeudi 11 Février 2010 à 16h30, salle 114

Adam Falkowski (Rutgers University) : Hidden Higgs seminairefalkowski2010, PDF - 2.1 Mo

I will talk about a class of models that allow the Higgs boson to be much lighter than the naive LEP limit of 114.4 GeV. This is possible because the Higgs searches at LEP are less sensitive to Higgs decaying into multiparticle final states. Recent theoretical ideas include models where the Higgs decays into (more than two) hadronic jets, or into lepton jets, which allow the Higgs to be as light as 90-100 GeV without violating any experimental constraints. I will discuss the prospects to discover such Higgs at Tevatron and the LHC, as well as in the old LEP data.


-  Jeudi 4 Février 2010 à 16h30, salle 114

Pablo Roig-Garces (LPT) : Recent improvements in our understanding of Tau decays seminaireroig2010, PDF - 1.8 Mo

A convenient framework to study hadron decays of the tau is that of Resonance Chiral Theory, an Effective Field Theory based on the following properties of QCD : its approximate chiral limit at low-energies, its large N_C limit and the known asymptotic behaviour of its form factors. We will present some ongoing developments in the decays to pi/K gamma nu and to eta pi pi nu and check the consistency with previous results in other three meson decay modes. Our results are being used to improve the description of the hadronization of QCD currents in hadron tau decays (TAUOLA) and the hadron cross section e^+e^- at low energies.


-  Jeudi 21 Janvier 2010 à 16h30, salle 114

Nazario Tantalo (Université de Rome) : A lattice study of semileptonic decays of B mesons into D^(*) mesons seminairetantalo2010, PDF - 1.7 Mo

I will discuss the results of a quenched lattice calculation of the decay rates of the semileptonic processes B—>D^(*) l nu at non vanishing momentum transfer. In particular, I will describe the strategies adopted to handle with heavy-light mesons on the lattice and to calculate three-point correlation functions at non-vanishing spatial momenta with reasonable accuracy. Finally, I will discuss the phenomenological relevance of these results in the extraction of the CKM matrix element |V_cb| from experimental data and some future developments.


-  Jeudi 14 Janvier 2010 à 16h30, salle 114

Séminaire à 2 voix : Mounir El Beiyad et Charles Bouchart (LPT)

1) Mounir El Beiyad : Structure des Hadrons dans les Réactions Exclusives

Les réactions exclusives en Chromodynamique Quantique permettent de déterminer les grandeurs des différentes caractéristiques de la structure des Hadrons. Cette étude théorique a permis de mettre en évidence notamment les Distributions de Partons Généralisées (GPD) et les Distributions d’Amplitude Généralisées (GDA) et leur intérêt phénoménologique. Je présenterai donc ces différentes notions, en mettant en avant la possibilité, via un processus physique particulier, d’extraire des informations sur la structure en spin du proton.

2) Charles Bouchart : Phénoménologie du Higgs dans le modèle de Randall-Sundrum seminairebouchart2010, PDF - 728 ko

Depuis une dizaine d’années, de nombreux modèles à dimension(s) supplémentaire(s) ont fait leur apparition, proposant des alternatives intéressantes à la SuperSymétrie pour tenter de résoudre le problème de hiérarchie. Je commencerai par présenter l’un de ces modèles, introduit par Lisa Randall et Raman Sandrum, dans lequel s’inscrivent mes travaux de thèse. Puis, j’introduirai la phénoménologie du Higgs dans ce modèle, ses différents couplages aux particules du modèle standard, et le rôle des mesures de précisions électrofaibles pour contraindre le modèle. Enfin, je concluerai sur les perspectives qu’offrent ce modèle.


-  Jeudi 7 Janvier 2010 à 16h30, salle 114

Cyrille Marquet (IPhT CEA/Saclay) : Forward particle production in dA collisions seminairemarquet2010, PowerPoint - 4.2 Mo

Single particle observables (inclusive spectra and nuclear modification factors) in d-Au collisions at RHIC are often quoted as evidence for the Color Glass Condensate (CGC), condisering the suppressed production at forward rapidities. Indeed, these kinematics probe partons in the nucleus that have a small fraction of momentum $x,$ and it is natural to expect non-linear QCD to play a role. Following the recent d-Au run at RHIC, new measurements provide further tests of the CGC picture. In particular, di-hadron correlations in azimuthal angle reveal the disappearance of the away-side peak at forward rapidities, in quantitative agreement with CGC predictions made earlier. I will review the theory and phenomenology of this "jet quenching phenomenon" in d-Au collisions, and argue that it completes the evidence that a nucleus probed at small-x is described by a CGC.


SOUTENANCE DE THESE

-  Vendredi 11 Décembre à 11h, salle 114

Emmanuel Chang (LPT Orsay) : QCD sur réseaux et les propriétés des mésons lourds-légers. Les distributions radiales dans les mésons lourds-légers et le mélange B^0-\bar B^0 dans la limite statique

La phénoménologie des mésons lourds-légers est étudiée à l’aide de simulations de QCD sur réseau. Le présent travail est particulièrement centré sur la dynamique du quark léger dans des systèmes lourds-légers lorsque le quark lourd est infiniment massif. La différence de masse entre l’état fondamental et les états excités est étudiée grâce à des données réseau "unquenched" possédant N_f=2 quarks légers dynamiques. Une très haute précision des résultats sur réseau pour les couplages d’un pion mou est obtenue en améliorant plusieurs aspects des précédents calculs sur réseau de ces couplages. De plus, ce travail propose une nouvelle méthode permettant de déterminer pour la première fois l’émission d’un pion au cours de la transition entre l’état fondamental et le premier état excité d’un méson lourd-léger. Ces couplages constituent des ingrédients nécessaires pour la description des mésons lourds-légers à l’aide d’une théorie effective connue sous le nom de Théorie Chirale des Perturbations pour les Mésons Lourds. Ils sont aussi essentiels pour l’extrapolation chirale des résultats obtenus sur réseau en matière de phénoménologie de la physique du B.

Nous portons un soin particulier à l’amélioration de la méthode employée pour calculer le propagateur du quark lourd statique sur réseau en utilisant les techniques de mise en bloc hyper-cubique (HYP). Nous procédons ensuite à une étude détaillée des éléments de matrice hadronique de tous les opérateurs \Delta B=2 à quatre quarks conservant la parité qui entrent dans la description théorique de l’amplitude du mélange B^0-\bar B^0 dans le Modèle Standard ainsi que dans ses extensions supersymétriques. C’est la première étude de ce genre avec des lignes de Wilson avec mise en bloc HYP, avec un bénéfice supplémentaire : le mélange spurieux d’opérateurs calculés sur réseau est nettement réduit par rapport aux travaux antérieurs sur le sujet. La renormalisation et le matching de la Théorie Effective de Quark Lourd sur réseau et de la QCD dans le continu est effectué en utilisant la théorie de perturbations boostée. Nous fournissons également une brève discussion de l’impact de nos résultats sur la phénoménolgie du méson B.


-  Jeudi 3 Décembre à 16h30, salle 114

Mathieu Segond (Leipzig) : Small-x resummation in collinear factorization

The resummation of the small-x corrections to hard scattering amplitudes in pQCD by collinear factorisation method is reconsidered and the resulting correction factor is derived in leading logarithm approximation. Our result is compared and disagrees with the corresponding expression by Catani and Hautmann (1994). The significance of the correction is demonstrated in the examples of the longitudinal structure function and of exclusive vector meson electroproduction. The formulation covers the channels of non-vanishing conformal spin $n$ paving the way for new applications.


SOUTENANCE DE THESE

-  Vendredi 27 Novembre à 11h, Amphi I

Benjamin Haas (LPT Orsay) : QCD sur réseau et physique du charme

We will present the results obtained on precision calculations of some charm quark properties relevant for phenomenology. As every quark, the charm quark interacts through the electroweak interaction and the strong interaction. At present, solving the strong interactions analytically is impossible. To compute the physical properties, we used a well-defined numerical and model-independent approach namely Lattice QCD. We used two different realizations of the Wilson quarks, namely the Wilson—Clover quark and the twisted mass quarks. When correctly tuned, both offer an O(a) improvement which is essential in studying the charm physics on the lattice. We worked out new techniques that reduce the systematic error so that a 1% accuracy can be achieved by only increasing the statistics. Moreover, we worked with Nf=2 quarks in the sea so that the main contribution to the quantum fluctuations of the vacuum has correctly been taken into account. The u/d quarks are always degenerated with the sea quarks so that the theory does not suffer from the breaking of unitarity that arises in quenched theories.

We studied the properties of the D*-meson decays in a comprehensive way which has never been done before. Our unquenched calculations of the coupling of D*-meson to the D-meson and the pion is an essential update of previous calculations. Among the new techniques we used, the twisted boundary conditions allowed us to control the momentum on the lattice in very fine way. We used this technique to devise the first calculation of the coupling of the D*-meson do the D-meson and the soft photon. We emphasize that from our computation we can confirm the compatibility of the experiment with the theory without making any assumption, and emphasize that our calculation should be improved in the future by just increasing the statistics.

We then significantly improved the calculations of the properties of the D-meson decays. We extracted the pseudoscalar and vector decay constants from simulations with Wilson-Clover quarks and twisted mass quarks. We also studied the coupling of the vector meson to the tensor density which can be helpful for constraining the physics beyond the Standard Model. Finally, we computed the vector and scalar form factors of the semileptonic decay of the D -> pi l nu decay. We also computed the tensor form factor that is interesting for studies of the new physics.

We finally combined all our results for studying the shape of the vector form factor and compare it with Vector Meson Dominance.


SOUTENANCE DE THESE

-  Vendredi 20 Novembre à 10h30, salle 114

Charles-Christophe Jean-Louis (LPT Orsay) : Secteurs de Higgs et neutrinos dans le NMSSM

Le NMSSM est une extension supersymétrique du Modèle Standard très bien motivée du point de vue expérimental et du point de vue théorique. En effet, ce modèle apporte une solution au problème mu du MSSM tout en étant moins contraint que ce dernier expérimentalement. Après un bref rappel des modèles supersymétriques les plus utilisés, nous discuterons la brisure de la supersymétrie par médiation de jauge dans le NMSSM, nous verrons ensuite que la brisure de R-parité permet de générer des masses pour les neutrinos à l’ordre de l’arbre tout en conservant un candidat viable pour la matière noire. Finalement, une possibilité de contraindre la supersymétrie via l’observation des neutrinos émis lors d’une supernova est analysée.


-  Jeudi 19 Novembre à 16h30, salle 114

Fu-Sin Lin (Université de Bruxelles) : Inert Multiplet Dark Matter and Direct Detection experiments

The addition of a new, odd under some parity symmetry and weakly interacting scalar multiplet provides a simple yet rich extension of the Standard Model which can account for Dark Matter. Direct detection experiments provide strong constraints on such models. When the additional multiplet is a doublet, two solutions provide a simultaneous fit of the DAMA modulation data and all the other constraints. Either the DM is light (mDM 10 GeV) and scatters elastically with a nucleus, with Higgs portal type scalar interactions. Either the DM is heavy (mDM 1 to 10 TeV) and scatters inelastically on nuclei, through a Z boson. For higher multiplets, at the renormalizable level, only multiplets with zero hypercharge are allowed. For real multiplets, the predicted signal is below current limits but above future ton sized experiments projections. If non renormalizable operators are allowed, suppressed by some cut-off scale, small mass splittings as needed for the inelastic solution of DAMA may naturally appear and rescue some models with non zero hypercharge.


-  Vendredi 11 Septembre à 11h, salle 100, LAL, Bâtiment 208

Séminaire LAL / LPT

N. Nikitin (Moscow State University) : Theoretical overview of the rare B-decays with leptons in the final state

In current talk we will present the theoretical overview for rare semileptonic and rare radiative leptonic decays. Additionaly we will compare the theoretical predictions with the experimental data and will consider the applications of the theoretical approaches to the Monte-Carlo Generators.