Laboratoire de Physique
Theorique d'Orsay

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

Séminaires Particules 2007-2008

Les séminaires se tiennent en salle 114 au 1er étage du bâtiment 210, généralement le jeudi à 16h30, sauf indication contraire.

Contacts pour les séminaires : Yann Mambrini et Sébastien Descotes-Genon.

-  Jeudi 10 Juillet à 16h30, salle 114

Gautam Bhattacharyya (Saha Institute, Kolkata) : Electroweak Symmetry Breaking and BSM Physics (A review)

I shall start with the electroweak symmetry breaking scenario, triggered by the Higgs mechanism, as envisaged in the standard model, and then I shall highlight some of its deficiencies making a case for the need to go beyond the standard model (BSM). The BSM tour will be guided by symmetry arguments. I shall discuss four specific BSM scenarios, namely, supersymmetry, Little Higgs, Gauge-Higgs unification, and the Higgsless models.

-  Mardi 1er Juillet à 16h30, salle 114

Pietro Colangelo (Université de Bari) : Aspects of holographic QCD

It has been proposed to extend the AdS/CFT duality conjecture to QCD-like theories. I shall describe this idea and the so-called bottom-up approach, discussing the main results and drawbacks of the models which are currently studied.

-  Jeudi 22 Mai à 16h30, salle 114

Yacine Mehtar-Tani (Univ. Heidelberg) : Initial state in high energy nucleus-nucleus collisions

High energy nucleus-nucleus collisions have become a subject of a large interest during the last decade, in particular when the RHIC project started. In such collisions one expects to probe QCD matter at high gluon density in a perturbative regime, the so-called saturation regime.

We have been interested in the early stages after the collision which set the initial conditions for the formation of the QGP. In the framework of the classical Yang-Mills equations, in light-cone gauge, we present a systhematic method to resum high density effects in both nuclei to calculate observables such as the gluon production cross-section. First, some general and exact results are derived such as the conserved current and the gauge field just after the collision. Then, we describe the method for solving the Yang-Mills equations as an expansion in powers of final state interactions (gluon merging). We calculate the first order and show that it amounts to calculating the gluon production cross-section in the absence of final state interactions At that order k_t-factorization breaks down.

-  Mardi 6 Mai à 16h30, salle 114

David Kaplan (Univ. Washington, Seattle) : Peering beyond our horizon with axions

Axions with decay constant greater than 10**12 GeV are ruled out, except in an anthropic inflationary scenario, where the initial misalignment angle appears fine-tuned. Unlike many other anthropic arguments, the anthropic axion is on rather solid ground since the a priori probability distribution is known, and the astrophysical consequences for different misalignment angles can be at least be estimated. I discuss the possibility that remnants of pre-inflationary inhomogenities could possibly be detected in such scenarios.

-  Jeudi 17 Avril à 16h30, salle 114

Dmitri Melikhov (Moscow & Vienna) : Can one reliably extract bound-state parameters from QCD sum rules ?

I discuss the extraction of decay constants and form factors of the individual bound states from QCD sum rules, with special emphasis on the assumptions involved in this extraction. Making use of explicit examples, it is shown that the standard procedures adopted in the method do not allow one to provide rigorous error estimates for the extracted parameters of the bound state. This represents an obstacle for using the results from QCD sum-rules for bound states in electroweak physics.

Séminaire exceptionnel

-  Jeudi 10 Avril à 11h30, salle 114

Noureddine Mohammedi (Univ. Tours)

Ce séminaire est une introduction pour non spécialistes aux transformations de dualité. Quelques applications issues de la physique des particules seront présentées.

-  Jeudi 3 Avril à 16h30, salle 114

Michele Frigerio (IPhT - CEA) : A tight link between baryogenesis and neutrino mass in SO(10) theories

The amount of the matter-antimatter asymmetry produced from leptogenesis depends on light neutrino data but also on several unknown parameters, related to the very high energy scale where lepton number is broken. In SO(10) Grand Unified Theories, leptogenesis models become more predictive, but the freedom in the choice of parameters is only partially reduced. In this talk I will point out that, in a new class of SO(10) models, one single coupling induces neutrino masses as well as a B-L asymmetry. The asymmetry is in fact proportional to Im [m*_11 (m m* m)_11], where m is the light neutrino mass matrix. Therefore, this new mechanism relates baryogenesis directly to low energy neutrino parameters.


-  Lundi 31 Mars à 14h, salle 114

Cyrille Marquet (RIKEN BNL) : Forward particle production in dA collisions

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. The next d-Au run at RHIC will allow to measure more observables and enable further tests of the CGC picture. In this seminar, I will consider forward inclusive dijets and focus on correlations in azimuthal angle. In my calculation, I include both multiple scattering and non-linear QCD evolution at small-x. I obtain that the azimuthal angle distribution is peaked back to back and broadens as the momenta of the measured particles gets closer to the saturation scale.


-  Vendredi 28 Mars à 16h, salle 114

Benjamin Fuks (Univ. Freiburg) : QCD resummation for Drell-Yan-like processes beyond the Standard Model

When studying the transverse-momentum (pT) distribution of a produced colorless final state (e.g. slepton pair in supersymmetric models or lepton pair in Z’ models), it is convenient to separate the large- and small-pT regions. For the large values of pT, the use of the fixed-order perturbation theory is fully justified, but in the small-pT region, the coefficients of the perturbative expansion are enhanced by powers of large logarithmic terms. Furthermore, at the production threshold, the mismatch between virtual corrections and phase-space suppressed real-gluon emission leads also to the appearance of large logarithmic terms. Accurate theoretical calculations must then include soft-gluon resummation in order to obtain reliable perturbative predictions and properly take these logarithms into account. We present precision calculations for slepton-pair and Z’ production at hadron colliders, matching transverse-momentum spectra, invariant-mass distributions and total cross sections obtained with the use of resummation with those obtained through pure perturbative calculations. We compare then the resummed results with those provided by Monte Carlo generators such as MC@NLO or PYTHIA, and study the impact of scale variations, parton densities, and non-perturbative effects.

-  Jeudi 27 Mars à 16h30, salle 114

Julien Lavalle (Université de Turin) : Searching for Dark Matter signatures in the antimatter spectrum

If dark matter is made of self-annihilating particles, one can search for signatures in the cosmic ray spectrum (gamma-ray and charged cosmic rays). While the LHC is about to start hunting some new physics, and while some high energy astrophysics experiments (e.g. PAMELA, GLAST) are about to provide new insights on the cosmic ray propagation in the Milky Way, it is worth estimating, as precisely as possible, the theoretical uncertainties associated with the indirect detection of dark matter. I will discuss these uncertainties in the frame of indirect detection of dark matter in the antimatter cosmic ray spectrum, especially with positrons and anti-protons. I will focus on two important points : (i) the cosmic ray propagation modelling (ii) the effect of dark matter cosmological sub-halos, invisible substructures which are expected to boost the dark matter annihilation rate in the Galaxy. I will finally show why the understanding of cosmic ray propagation is a key element in the searches for dark matter signatures, even in the gamma-ray spectrum.

-  Jeudi 20 Mars à 16h30, salle 114

Emi Kou (LPT) : Searching for signals beyond SM in B meson decays

I will discuss the recent topics from B factory experiments and their theoretical issues. First part of my talk, I will overview the current status of the determination of the CKM matrix, the new physics search in the CP violating B decays, the new hadron spectroscopy. I will also present some physics cases in the current and future B physics experiments, namely Babar, Belle, LHCb and SuperB factories. Second part of my talk, I will present our recent results on the B\to l\nu process. B\to l\nu is one of the most important processes where a new physics effect may manifest itself. I will discuss the issues of the large background coming from the radiative leptonic B decays, B_{u}\to l\nu\gamma .

-  Jeudi 13 Mars à 16h30, salle 114

Peter Orland (Bohr Inst. & CUNY, Baruch Coll.) : Near-Integrability in 2+1- and 3+1-dimensional Yang-Mills theories

Simple arguments are used to show that confinement and a mass gap occur in weakly-coupled, anisotropic non-Abelian gauge theories in 2+1 dimensions. Such theories may be regarded as coupled non-linear sigma models, and consequently are completely integrable in a certain limit. More sophisticated techniques yield accurate expressions for the mass spectrum and the interquark potential. In 3+1 dimensions, similar techniques can be used for a hybrid model with both strong and weak couplings. This hybrid model was proposed long ago as an effective theory of high-energy hadron-hadron collisions by Verlinde and Verlinde.

Séminaire informel

-  Mardi 11 Mars à 11h, salle 114

Constantia Alexandrou (Université de Chypre) : Hadron Structure from Lattice QCD

-  Jeudi 6 Mars à 16h30, salle 114

Gregorio Herdoiza (DESY Zeuthen) : Physical results from dynamical simulations with twisted mass fermions

I will present the results from large-scale lattice QCD simulations using two flavours of twisted mass fermions at maximal twist in the vicinity of the chiral limit. The scaling to the continuum limit of simple hadronic observables as well as the description of their quark mass and volume dependence through chiral perturbation theory will be discussed.


-  Mardi 4 Mars à 16h30, salle 114

James Drummond (LAPTH) : Hidden symmetries of gluon amplitudes and Wilson loops

We will summarise recent progress in uncovering a ’dual’ conformal symmetry of gluon amplitudes in supersymmetric Yang-Mills. The symmetry seems to be part of a mysterious duality between gluon amplitudes and Wilson loops and we will discuss the evidence for this.

Séminaire commun LAL-LPT

-  Mardi 26 Février à 11h au LAL, Orsay, Bâtiment 200, salle 101

Georges Zoupanos (National Technical University Athene, Greece) et Sven Heinemeyer (IFCA (CSIC-UC), Santander, Spain) : Finite Unified Theories : Predictions for the lightest Higgs mass and other collider observables

Finite Unified Theories (FUTs) are N=1 supersymmetric Grand Unified Theories that can be made all-loop finite. The requirement of all-loop finiteness leads to a severe reduction of the free parameters of the theory and, in turn, to a large number of predictions. FUTs are investigated in the context of low-energy phenomenology observables. These comprise predictions for the top and quark bottom masses, the lightest Higgs boson mass, the anomalous magnetic moment of the muon, B physics observables and constraints from cold dark matter densities. These predictions can directly be tested at todays and at future accelerator experiments.

-  Jeudi 21 février à 16h30, salle 114

Marco Cirelli (CEA, Saclay) : Neutrino Properties from Cosmology : the usual and the less usual

Cosmology is currently one of the most powerful probes of the properties of neutrinos (and of possible new light particles), thanks to the fact that neutrinos play an important role in the evolution of the cosmological perturbations that we are observing today with high precision. How massive are neutrinos ? How many neutrinos there are ? Are they cosmologically freely streaming or they can be "sticky" ? Are there new light particles ? I discuss how global fits of cosmological data from the Cosmic Microwave Background, Large Scale Structure and Supernovae can answer these questions and raise a few interesting points.

Based on : astro-ph/0607086, JCAP 0612 (2006) 013


-  Jeudi 14 Février à 16h30, salle 114

David Kaplan (Univ. Washington, Seattle) : Lattice supersymmetry

In recent years there has been a lot of progress in understanding how to construct a class of supersymmetric lattice gauge theories, using string theory derived technology. I explain the general features of such theories, and how they work.

-  Jeudi 7 Février à 16h30, salle 114

Gianfranco Bertone (IAP) : Dark Matter : a multi-disciplinary approach

After a brief introduction to the Standard Cosmological Model that has emerged from the precision measurements carried out in the last two decades, I will focus on one of its pillars, Dark Matter. I will show that a complete understanding of its nature requires a multi-disciplinary approach, where the information from accelerator, direct and indirect searches is combined in a consistent theoretical framework. I will conclude with some remarks on the role that astrophysical observation can play in the identification of Dark Matter.

Séminaire informel

-  Mardi 5 Février à 11h30, salle 114

Franco Buccella (Université de Naples) : A propos de la théorie exceptionnellement simple basée sur le groupe exceptionnel E8

-  Jeudi 17 Janvier à 16h30, salle 114

Franco Buccella (Université de Naples) : Spectrum of positive and negative parity pentaquarks

By assuming that the chromomagnetic interaction plays the main role for the mass splittings of the positive and negative parity pentaquarks, one finds good agreement with the present experimental situation.

-  Jeudi 10 Janvier à 16h30, salle 114

Gavin Salam (LPTHE Jussieu) : Jets, our window on partons at the LHC

Jets, collimated bunches of hadrons that result from the fragmentation of quarks and gluons, will be key observables at LHC. This talk introduces the issues that are relevant in hadron-collider jet-physics and reviews recent developments. These include both technical breakthroughs, finally enabling hadron-collider jet-finding to be brought up to the standards set out in the 1990 Snowmass accord, and progress in understanding the physics of jets, which serves as groundwork for optimising the practical effectiveness of jet-finding at LHC.

-  Jeudi 20 Décembre à 16h30, salle 114

Lorenzo Calibbi : Neutralino Dark Matter and tau polarization : a way to distinguish SUSY-GUT from CMSSM ?

n the context of low-energy Supersymmetry (SUSY), a model of Grand Unification (GUT) with right-handed (RH) neutrinos is discussed and its implications for neutralino dark matter (DM) are studied and compared with the constrained MSSM (CMSSM). Renormalization Group effects in this model modify the supersymmetric spectrum such that the WMAP limit on the DM relic density cannot be satisfied for small values of tanbeta and the region of the parameter space allowed by efficient neutralino-stau coannihilation presents a peculiar phenomenology and an upper bound on the neutralino mass for most of the parameter space. Then we show how the study at the International Linear Collider (ILC) of the polarization of tau coming from stau decays can offer a very good handle for distinguishing between CMSSM and the SUSY-GUT scenario, at least in the case of stau coannihilation region.

-  Jeudi 29 Novembre à 16h30, salle 114

Peter Zerwas (DESY) : Supersymmetry at LHC/ILC : Base for Unification

Supersymmetry provides a stable bridge from the electroweak to the grand-unification scale. The LHC and TeV e+e- linear colliders will be integral instruments in exploring the supersymmetry sector, and coherent analyses can draw a comprehensive and high-resolution picture. This may serve as a solid platform for extrapolations to the fundamental physics domain near the grand-unification and Planck scale. The potential of such analyses will be examined for minimal supergravity, left-right symmetric extensions involving intermediate scales, and string effective theories.

-  Jeudi 8 Novembre à 16h30, salle 114

Guy F. de Téramond (CPhT, Ecole Polytechnique) : AdS/QCD and the Holographic Light-Front Representation

The gauge/gravity correspondence provides new insights into the confining dynamics of QCD in its strongly coupling regime, such as the orbital and radial spectra and the behavior of form factors in the space-like and the time-like regions. We derive light-front equations describing the propagation of extended hadronic modes, from the semiclassical approximation to the equations of motion of bosonic and fermionic modes on AdS space and the mapping of string modes to light-front wavefunctions of hadrons in physical space-time. The effective equations describing light-front eigenmodes in 3+1 space-time depend on the average impact distance between the constituents and possesses remarkable algebraic structures and integrability properties dictated by the conformality of the theory. The holographic model is extended to include a confining potential while preserving its algebraic structure.

-  Jeudi 25 octobre à 16h30 , salle 114

Carlos Munoz (Universidad Autonoma de Madrid) : Proposal for a new supersymmetric Standard Model

Although supersymmetry is thirty five years old, it is still one of the most attractive theories for physics beyond the standard model. Assuming that it will be discover at the LHC, the question is : What supersymmetric model do we expect to be right one ? After reviewing briefly several models that have been proposed in the literature, such as the MSSM, NMSSM, BRpV, etc., we will propose a new one. Its interest resides in the fact that it introduces a solution to the (crucial) $\mu$ problem of supersymmetric models that is connected to the (nowadays very important) neutrino physics.

-  Jeudi 27 septembre à 16h30 , salle 114

David Cerdeno (Madrid) : Towards the Identification of Dark Matter

The potential identification of WIMP dark matter candidates in direct detection experiments which are simultaneously sensitive to both spin-dependent and spin-independent couplings is investigated. The particular cases of the neutralino in supersymmetric theories and Kaluza-Klein dark matter in models with universal extra dimensions are studied through the determination of the theoretical predictions for their axial and scalar couplings. A case study is done for the COUPP experiment (Chicagoland Observatory for Underground Particle Physics), whose projected sensitivity could allow the exploration of a part of the parameter space of both WIMP candidates. Furthermore, the possibility of employing different detection liquids provides a significantly more precise determination of the WIMP axial and scalar couplings. This possibly allows the discrimination between neutralino and Kaluza-Klein dark matter.