Laboratoire de Physique
Theorique d'Orsay

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Bâtiment 210
Univ. Paris-Sud 11
91405 Orsay Cedex
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Agenda > Séminaires / Seminars > Particules Dernier ajout : jeudi 2 octobre 2014.

Séminaires Particules 2006-2007

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 Dominique Schiff.

-  Lundi 16 Juillet à 16h, Auditorium Pierre Lehmann du LAL, Bâtiment 200, Séminaire commun LAL/LPT

Ikaros Bigi (Notre Dame du Lac) : “This Year a New Era Has Commenced & You Can Say You Have Been Present”
— Goethe, the Cannonade of Valmy and Charm Transitions

After a Prologue on New Physics scenarios and the uniqueness of charm to find them I briefly describe predictions for $D0$ oscillation rates in the Standard Model and their uncertainties and review the experimental evidence for such oscillations. My main message is that searches for CP violation in D transitions are a powerful and reliable probe for New Physics, and I lay out the phenomenological landscape for them.

-  Jeudi 5 Juillet à 16h 30

Emilian Dudas (LPT et CPhT X) : Modèles supersymétriques et brisure de supersymétrie à basse énergie

La supersymétrie de basse énergie est le candidat pricipal pour une nouvelle physique à découvrir au LHC. Je vais passer en revue les efforts faits pour les constructions explicites des modèles avec brisure spontanée de supersymétrie et leur propriétés à basse énergie. Des développements récents des modèles avec basse échelle de brisure de supersymétrie seront mentionnés.

-  Jeudi 21 Juin - PAS DE SEMINAIRE


Réunion plénière du GDR "Physique Nucléaire et Calculs sur réseau"

-  Jeudi 7 Juin à 16h 30

Lech Szymanowski (LPT Orsay/SINS Varsovie) : Exclusive J/psi and Upsilon hadroproduction and the QCD odderon

The total cross sections of hadronic processes are driven by colour singlet exchanges in the t—channel. Thus, pomeron exchange, characterized by an even charge parity, gives the dominant contribution to the sum of the direct and the crossed amplitudes for a given hadronic process. The exchange with the odd charge parity, i.e. that of the odderon, dominates the difference between these two amplitudes. The concept of the odderon in the description of hadronic processes was introduced more than 30 years ago. Although it is a partner of the pomeron, which is well known e.g. from the study of diffractive processes, the odderon still remains a mystery and escapes experimental verification. I shall first introduce a concept of the odderon and I’ll discuss some recent suggestions to look for the odderon effects in certain specific processes. Next, I shall present my recent work in which we study proton-proton and proton anti- proton collisions which lead to the exclusive production of J/psi or Upsilon from the pomeron-odderon and the pomeron-photon fusion. As result we obtain estimates of cross sections for the kinematic conditions of the Tevatron and of the LHC.

-  Jeudi 31 Mai à 16h30

Karl Jansen (DESY, Zeuthen) : The Quest for Solving QCD : Simulations with Light Quarks

The strong interactions of elementary particles are described theoretically in the framework of Quantum Chromodynamics (QCD). The solution of QCD is an outstanding problem in modern particle physics. The most promising way is given by numerical simulations using Monte Carlo Methods, in which the space-time continuum is replaced by a lattice. We shall demonstrate that since the invention of this approach by K. Wilson the conceptual, algorithmic and computer developments have progressed so much that today realistic simulations of lattice-QCD become possible, bringing us close to a, at least, numerical solution of QCD.

-  Mardi 29 Mai à 14h30 JOUR et HEURE INHABITUELS

Olivier Leitner (Frascati) : Testing CP and Time Reversal Symmetries in \Lambda(b) Decays into Polarized Resonances

Putting together kinematical and dynamical analysis we present a complete study of the decay channels \Lambda_b into \Lambda and a vector meson V (J/\Psi or \rho_0), with a subsequent decay of \Lambda to p \pi^- and V(J/\Psi) to \ell^+\ell^- or V(\rho_0) to \pi^+ \pi^-. An intensive use of the helicity formalism is involved on the kinematical side, while on the dynamical side, HQET is applied to determine the hadronic matrix elements between the baryons \Lambda_b and \Lambda. CP and time reversal symmetries are investigated in these channels where the major role of the \Lambda_b polarization for constructing T-odd observables is emphasized. Finally, it will be also shown that the normal component of a polarization vector, as defined in the Jackson’s frame, is Lorentz invariant and could get large values : as a result, the normal component becomes a serious candidate to cross-check Time-reversal symmetry.

-  Vendredi 25 Mai à 14h30 - JOUR et HEURE INHABITUELS

Xavier Calmet (ULB, Bruxelles) : Minimal extensions of the Higgs sector of the Standard Model

We discuss some simple extensions of the Higgs sector of the Standard Model which would lead to some interesting phenomenology at the LHC. Some of these models allow to link the electroweak symmetry mechanism to dark matter. Others could lead to some noncommutative effects in the Higgs sector and/or in the dark matter sector.

-  Jeudi 24 Mai à 16h30

J.B. de Vivie (CERN) : A very brief overview of the LHC machine, detectors and physics

The CERN Large Hadron Collider should start its operations during the year 2008 at an unprecedented centre-of-mass energy of 14 TeV and at high luminosities. It will allow the TeV scale to be thoroughly studied and should provide new answers or hints to the Electro-Weak Symmetry Breaking puzzle. In this seminar, a brief introduction to the LHC accelerator and experiments will be given, in particular the ATLAS detector will be described with some details. Topics, selected among the most prominent ones on the LHC physics potential, will be presented. The expectations from the first collisions in 2008 and 2009 will also be briefly reviewed.

-  Mardi 15 Mai à 16h30 - JOUR EXCEPTIONNEL

Francesco Hautmann (CERN) : Parton distribution functions in an s-channel approach

Deep inelastic scattering at low x has been studied extensively at HERA. This provides valuable input for the LHC program, where the short-distance structure of protons and nuclei will be probed at TeV energies. This talk discusses the use of s-channel methods in QCD to investigate parton distribution functions at small momentum fractions, and effects of multiple scattering in hadron collisions at very high energies.

-  Vendredi 11 Mai à 16h30 - JOUR EXCEPTIONNEL

Pierre Hosteins (CEA, Saclay) : Dualité de seesaw et leptogénèse

Jusqu’ici les mécanismes de seesaw de type I ou II purs ont été étudiés pour donner une faible masse aux neutrinos. Après quelques rappels sur les théories de Grande Unification et la supersymétrie, nous considérerons des théories ou les types I et II sont fréquemmentprésents avec des magnitudes comparables et nous présenterons une méthode pour extraire de la formule du seesaw la matrice de masse des neutrinos droits lourds à partir des paramètres de basse énergie. On peut alors explorer les prédictions de ces théories pour la leptogénèse et la violation de saveur leptonique, qui sont beaucoup plus riches que pour le seesaw traditionnel.

-  Jeudi 10 Mai à 16h 30

Oleg Lebedev (CERN) : MSSMs from strings

I will report on recent progress in realizing the exact MSSM spectrum in the heterotic string. I will discuss the underlying concept of `local grand unification’ and present some phenomenological implications, for example, for the scale of SUSY breaking.

-  Mercredi 9 Mai à 16h30 - JOUR EXCEPTIONNEL

Rikard Enberg (LBL, Berkeley) : LHC and Dark Matter Signals of Improved Naturalness

The Standard Model Higgs suffers from the hierarchy problem, typically implying new states within the reach of the LHC. If the Higgs is very heavy ( 500 GeV) the states that cutoff the quadratic divergence may be beyond the reach of the LHC. However, in this case the SM must be extended with new light particles. I will discuss a very simple extension of the SM, with no new colored states, which allows such a heavy Higgs whilst remaining consistent with experiments, and yielding the correct dark matter abundance. We investigate the possibilities for its discovery at the LHC and future dark matter detection experiments.

-  Lundi 7 Mai à 14h30 - JOUR EXCEPTIONNEL

Urko Reinosa (Heidelberg) : Action effective deux-particules-irréductible et applications à la théorie des champs à température finie

L’action effective deux-particules-irréductible (2PI) est une méthode de calcul en théorie des champs permettant d’aborder certaines questions (par exemple les phénomènes hors-équilibre) inaccessibles à des méthodes plus conventionnelles comme la théorie des perturbations ou le réseau.

En tant que méthode non-perturbative, son implémentation pratique passe par un certain nombre de difficultés techniques devant être résolues au préalable. Il s’agit de difficultés théoriques relatives à la renormalisation ainsi que de difficultés numériques ayant trait à la résolution d’équations intégrales non-linéaires qui sont au coeur de l’approche 2PI.

Après une présentation de la méthode, je passerai donc d’abord en revue les progrès récents concernant la renormalisation de l’action effective 2PI et le développement de techniques permettant de résoudre les équations intégrales associées. J’aborderai ensuite un certain nombre d’applications de la méthode en particulier l’étude du diagramme des phases de QCD et l’étude du modèle sigma linéaire à température finie.

-  Vendredi 4 Mai à 14h15 - JOUR EXCEPTIONNEL Horaire modifié - Amphi 2, 2ème étage -

Cristina Timirgaziu (Liverpool University) : Modèles de fermions libres et compactifications par orbifold

Les modèles de fermions libres représentent une approche particulière à l’obtention des modèles de cordes en quatre dimensions. Ils génèrent des théories de basse énergie parmi les plus réalistes jusqu’à présent et ce d’une manière simple et élégante. Toutefois, ces modèles, du fait de leur construction, n’offrent pas une image géométrique intuitive. Les compactifications par orbifold, d’un autre côté, offrent un cadre géométrique plus intuitif, qui permet, entre autre, de comprendre l’origine géométrique de certaines propriétés intéressantes du point de vue phénoménologique.

Il existe des indications que les modèles de fermions libres correspondent à des compactifications par orbifold des tores non factorisables, à un rayon fixe, plus précisément à des orbifolds Z2 x Z2 du réseau SO(12). Ceci peut servir d’inspiration dans la recherche des modèles d’orbifold semi-réalistes. Après une introduction générale aux modèles de fermions libres et aux compactifications par orbifold, je discuterai les compactifications par orbifold des tores non factorisables et le rôle des conditions au bord asymétriques dans les modèles de fermions libres.

-  Jeudi 3 Mai à 16h 30

Séminaire "Etudiant" à 2 voix

  • Benjamin Basso (LPT, Orsay) : Anomalous dimensions of high-spin operators beyond the leading order

The success of QCD as the theory of strong interactions relies in part on the possibility to predict the scale dependence of various physical observables. In the most prominent example of deeply inelastic scattering, this dependence is governed by anomalous dimensions of composite operators. The anomalous dimensions depend on the coupling constant as well as on the quantum numbers of operators (Lorentz spin,...) and their properties reflect the symmetries of the underlying gauge theory. Their analytic expressions beyond the leading order are cumbersome and difficult to study. In their more tractable large spin expansions, anomalous dimensions exhibit an interesting structure that we will discuss.

  • Mathieu Remazeilles (LPT, Orsay) : Brane World Cosmology and Signatures of Extra-Dimensions

Dissipation and non-locality are fundamental processes from the point of view of an observer localized on a 3-brane. By studying these intrinsically higher-dimensional effects in brane world models, it is hoped to find some distinctive observational signatures for the presence of extra-dimensions.

In this talk we present the Randall-Sundrum model (RS II), which is a phenomenological realization of localization of 4D gravity on a brane in spite of the presence of an infinite extra-dimension. Then we present a sketch of work on the modelling of dissipative effects by asking what is the probability for a would-be bound state to escape from a brane with an arbitrary expansion history into the bulk ?

-  Jeudi 26 Avril à 16h 30

Alberto Romagnoni (LPT, Orsay) : Non(anti)commutative geometry and N=1/2 field theories

Euclidean geometries in superspace, with nonanticommuting spinorial coordinates, can appear as low energy limit of string theory in a particular RR background. The corresponding deformed field theories preserve only half of the supersymmetry, and therefore the known theorems about the quantum properties of the original theories are no longer valid. I will discuss the new features arising in this framework, mainly focusing on gauge invariance and renormalizability of N=1/2 SYM theories.

-  Mardi 24 Avril à 14h 30 ATTENTION : Horaire exceptionnel

A.B. Kaidalov (ITEP, Moscou) : Final state interactions in B-decays

The role of final state interactions in B-decays is investigated. A model with soft rescatterings of low mass intermediate states is suggested. The model explains a large difference in phases of amplitudes in B\to\pi\pi and B\to\rho\rho decays. Direct CP-violation asymmetries in B\to\pi\pi decays are calculated and results for the CKM angle \alpha are presented.

-  Jeudi 12 Avril à 16h 30

M.N. Chernodub (ITEP, Moscou) : Magnetic component of Yang-Mills plasma

Confinement in non-Abelian gauge theories is commonly ascribed to percolation of magnetic monopoles, or strings in the vacuum. At the deconfinement phase transition the condensed magnetic degrees of freedom are released into gluon plasma as thermal magnetic monopoles. We show that right above the critical temperature the monopole density remains a constant function of temperature, as for a liquid, and then grows, like for a gas. We also review briefly lattice data on the magnetic strings which refer mostly to SU(2) and SU(3) pure Yang-Mills theories and concentrate on implications of the strings for the Yang-Mills plasma. We argue that magnetic strings might be a liquid component of the Yang-Mills plasma and suggest tests of this hypothesis.

-  Mercredi 11 Avril à 14h 30 ATTENTION : Jour et Heure exceptionnels

Tobias Hurth (CERN) : Flavour in the Era of the LHC

We discuss the opportunities in our search for ’new physics’ beyond the standard model offered by present and future flavour experiments and show their complementarity to collider physics. Within this talk we focus on rare B and Kaon decays. Moreover, we briefly discuss the restrictive role of long-distance strong interactions in flavour physics and some new tools like QCD factorisation and soft-collinear effective theories (SCET) to handle them.

-  Jeudi 5 Avril à 16h 30

Micaela Oertel (LUTH , Observatoire de Meudon) : A-t-on observé le couplage des quarks droits au W ?

La mesure récente du facteur de forme scalaire K\pi dans la désintégration K^L_{\mu 3} par la collaboration NA48 indique une déviation de 5\sigma par rapport à la prédiction du modèle standard basée sur le théorème de Callan-Treiman. Cette déviation peut difficilement être expliquée dans le cadre de la seule QCD suggérant plutôt une manifestation de la physique au-delà du modèle standard. Je montrerai qu’un couplage direct des quarks droits au W explique l’effet sans contradiction avec d’autres contraintes expérimentales. Ces couplages apparaissent naturellement dans la théorie effective minimale non découplante (LEET) pour le secteur électrofaible à l’ordre sous-dominant. A cet ordre la LEET prevoit également des modifications des couplages des fermions au Z. Je montrerai que des valeurs cohérentes pour les couplages non-standard aux W et Z émergent d’une analyse de la théorie effective à l’ordre sous-dominant. Entre autre, il est possible de résoudre l’anomalie A_{FB}^b observée au LEP.

-  Jeudi 29 Mars à 16h 30

Giancarlo Rossi (Université de Rome, Tor Vergata) : Progress in lattice QCD : a Computational Challenge

After a short introduction on some of the computational challenges that today’ research is posing to our imagination, I will concentrate on lattice QCD, showing how recent technical and conceptual advances are providing us with an accurate understanding of hadronic physics, as well as a good control of the strong interaction effects relevant in our quest for new physics.

-  Jeudi 22 Mars à 16h 30

Adam Falkowski (CERN) : Randall-Sundrum reloaded

Randall and Sundrum proposed 5D theories in a slice of AdS5 as a solution to the hierarchy problem. Recently, there has been some progress in understanding this scenario. Ingredients necessary for the model to be phenomenologically viable have been identified. Holographic relations with 4D strong dynamics have been explored. Finally, simple techniques have been proposed that allow to extend the studies to an arbitrary 5D background. In this talk I will discuss these theoretical developments together with the expected experimental signatures.

-  Jeudi 15 Mars à 16h 30, exceptionnellement dans l’AMPHI 2, 2ème étage du bât. 210

Adrian Dumitru (Johann Wolfgang Goethe Universität, Frankfurt) : Using pA to constrain the initial state of AA collisions

Understanding the initial distribution of produced gluons in momentum and coordinate space is a crucial factor for determining the subsequent hydrodynamic expansion of the hot and dense matter produced in AA collisions at RHIC and LHC. I give a few examples of what needs to be understood and why, and how careful studies of pA collisions could help to solve some of these issues.

-  Jeudi 8 Mars à 16h 30

Mathieu Segond (LPT, Orsay) : Diffractive production of rho meson pairs in e+e-Collisions

The exclusive reaction of rho meson pair electroproduction in gamma*-gamma* collisions is a beautiful laboratory to study various dynamics and factorization properties in the perturbative sector of QCD. This process seems to offer a promising probe of the BFKL resummation effects which could be studied in the next generation of e+e- colliders (ILC) and at lower energy a way to explore QCD factorizations involving generalized distribution amplitudes (GDA) and transition distribution amplitudes (TDA).

-  Jeudi 22 Février à 16h 30

  • François-Xavier Josse-Michaux (LPT, Orsay) : Flavour-related questions in leptogenesis

Leptogenesis is an appealing mechanism to explain the observed baryon asymmetry of the Universe. Its recent developments include the effect of the heavier neutrinos and the role of the lepton flavours on its dynamic. In this talk i will shortly review those refinements.

  • Nicolas Bernal (LPT, Orsay) : Le MSSM avec des scalaires lourds

Nous allons présenter le MSSM dans la limite où les superpartenaires scalaires sont assez lourds, avec des masses $\gtrsim$ 10 TeV. Dans ce scénario, on peut découpler ses sparticules tout en conservant l’unification des couplages de jauge et le candidat pour la matière noire : le neutralino le plus léger. La détermination du spectre est faite grâce à l’implémentation d’une sous-routine pour le code SuSpect. Nous avons étudié les contraintes expérimentales, notamment celle donnée par la densité relique de matière noire. Une analyse phénoménologique des processus de production et de désintégration pour le Higgs et les sparticules sera présentée.

-  Jeudi 15 Février à 16h 30

Bernard Pire (CPhT, Ecole Polytechnique) : Dessine-moi un proton !

Ce que les processus exclusifs nous enseignent sur les hadrons.

La description factorisée des processus exclusifs durs en QCD permet de mesurer des éléments de matrice hadroniques à partir desquels on espère voir émerger une image cohérente du proton. On présentera les propriétés essentielles et la signification (par ordre d’entrée en scène)

des Amplitudes de distributions (DA),

des Distributions de partons généralisées (GPD),

des Amplitudes de distributions généralisées (GDA) et

des Amplitudes de distribution de transitions (TDA).

Le programme de mesure ne fait que commencer mais les premières indications sont très encourageantes.

-  Jeudi 8 Février à 16h 30

Philippe Brax (CEA Saclay) : Breaking Susy and stabilising moduli at low scale

I will discuss the problem of supersymmetry breaking from a string-inspired perspective. In particular, the issue of moduli stabilisation will be reviewed. Attempts to describe supersymmetry breaking with a low gravitino mass will be presented. In this setting the soft breaking terms are obtained and some of the phenomenological consequences can be analysed.

-  Mardi 6 Février à 14h 30 JOUR ET HEURE EXCEPTIONNELS

Alexander Gorsky (ITEP) : Induced tunneling in quantum field theory and particle decay in a false vacuum

I will discuss tunneling phenomena in field theory such as false vacuum decay or pair production in a strong external field. The induced tunneling phenomenon involves some particles in the initial state. I will show how to calculate the probability of the induced process and consider examples of particle decay in a false vacuum and monopole decay in an external electric field.

-  Jeudi 1er Février à 16h 30 - Deux séminaires de 40’ chacun

  • Carla Biggio : Neutrino masses and unitarity of the leptonic mixing matrix

Models of neutrino masses usually involve new physics at energies higher than the electroweak scale. One of the possible low energy effects is the appearance of deviations from unitarity in the leptonic mixing matrix. Usually this is assumed to be unitary and neutrino oscillations experiments are used to determine its parameters. I will discuss how relaxing the hypothesis of unitarity affects neutrino physics, both oscillations and other electroweak processes. I will then use them to constrain the matrix elements, showing in particular that now oscillation experiments alone are not enough to determine all the parameters, while combining them with electroweak decays we are able to recover the standard result.

  • Chloé Papineau (LPT, Orsay) : Moduli stabilization and uplifting with dynamically generated F-terms

Over the last decade, a lot of activity has been achieved in order to get a dynamically generated supersymmetry breaking, which ensures a low energy breaking scale. Last year, a model for SUSY QCD proposed to get such a breaking in a meta-stable vacuum, while supersymmetric vacua were present elsewhere in the field space. The lifetime of the susy breaking vacuum can be made arbitrarily long, and its energy is positive, related to the constants of the theory. On the other hand, in 2003, KKLT proposed a setup in which they could generate a potential for all of the extra fields which arise when reducing the theory to 4d. The main problem is that they ended up with a negative cosmological constant i.e an AdS vacuum. An uplifting mechanism is required to eventually obtain a small positive vacuum energy. We propose to combine the two scenarios so that the uplifting needed from moduli stabilization theories is realized by the supersymmetry breaking sector. I will present both setups, their combination, and the condition under which the gravitino is in the TeV range. I will eventually compute some of the tree-level soft masses.

-  Jeudi 25 Janvier à 16h 30

Dieter Müller (Ruhr Universität Bochum) : Theory and phenomenology of exclusive hadronic processes

Hard exclusive processes allow to resolve the internal structure of hadrons and even nuclei from a new perspective. The non-perturbative information about the partonic content, encoded in generalized parton distributions and distribution amplitudes, is complementary to those obtained from inclusive measurements. In this talk I outline the theory and review its status. Its phenomenological application will be shortlydiscussed for the hard photon electroproduction. In particular, a new representation of generalized parton distributions and hadronic amplitudes as Mellin-Barnes integral will be presented. This representation allows for a flexible parameterization of generalized parton distributions, it can be used for a fast and stable numerical evaluation of observables, and is the key to improve the theoretical framework beyond next-to-leading order accuracy.

-  Jeudi 18 Janvier à 16h 30

Marcos Sampaio (LPT, Orsay) : Symmetry Preserving Implicit Regularization Framework

The construction of a computational friendly invariant regularization technique which both operates in the physical dimension of the underlying model and preserves its vital symmetries is presented. In such regularization independent framework, which we call implicit regularization, momentum routing invariance in the loops is closely related to gauge supersymmetry invariance at arbitrary loop order.

-  Jeudi 11 Janvier à 16h 30

Egle Tomasi-Gustafsson (DAPNIA/SPhN, CEA/SACLAY ) : Facteurs de forme électromagnétiques : une sonde privilégiée pour la compréhension du nucléon

Les possibilités ouvertes par les accélerateurs et les collisionneurs à haute intensité donnent des perspectives nouvelles pour l’étude de la structure du nucléon. Des mesures récentes de polarization en diffusion élastique électron-proton ont montré que les distributions électrique et magnétique à l’intérieur du proton sont différentes et que le facteur de forme électrique du neutron n’est pas nul. On discutera les implications de ces résultats, et on soulignera la necessité d’une description unifiée dans tout le domaine cinématique (region espace et region temps), au vue de différents aspects : structure des noyaux legers, transitions vers le regime asymptotique prédit par la Chromodynamique Quantique, mecanismes de réaction, corrections radiatives.

-  Mardi 9 Janvier à 14h 30 - JOUR ET HEURE EXCEPTIONNELS

O.W. Greenberg (Department of Physics, University of Maryland) : The Discovery of Color ; a Participant Viewpoint

I will review the experimental discoveries and the theoretical climate in the period before the quark model, then discuss the events that led to the introduction of color as a classification symmetry, and close with comments about introduction of the gauge theory of color (QCD).

-  Lundi 18 Décembre à 14h 30, Séminaire commun LPT/CPhT-X de Physique des Particules

Florian Schwennsen (Université de Hambourg) : NLO BFKL at work - jet production in kT-factorization and angular decorrelation

In this talk I present the construction of a NLO vertex for the production of a jet at central rapidity in kT-factorization. For the case of hadron-hadron scattering it is accompanied by the introduction of a NLO unintegrated gluon density. Furthermore, I present recent results on the implementation of the NLO BFKL Green’s function to describe the angular decorrelation between Mueller-Navelet jets.

-  Jeudi 14 Décembre à 16h 30

Arif Shoshi (Université de Bielefeld) : QCD at high density and high energy

Over the last two years there has been a tremendous progress towards understanding high density QCD at high energy. The main progress consists in the understanding of gluon number fluctuations (or Pomeron loops) in the QCD evolution ; Evolution equation have been established that take into account the fluctuations, a relation between high density QCD and statistical physics has been found that allows us to study the effects of fluctuations on scattering amplitudes, etc. I will discuss in my talk some of the main steps of this recent progress.

-  Lundi 4 Décembre à 14h 30, Séminaire commun LPT / CPhT (Ecole Polytechnique)


Albrecht Kyrieleis (Manchester) : Superleading Logarithms - the Breakdown of QCD Coherence ?

Soft gluon radiation plays an important role for the understanding of a wide range of measurements and is of various theoretical interest. This radiation is calculated in perturbative QCD by resummation of leading logarithms. We have recently found the possible breakdown of QCD coherence which arises as a result of wide angle soft gluon emission developing a sensitivity to emission at small angles. This breakdown leads to the appearance of superleading logarithms. I present the calculation of the gaps-between-jets cross section as a concrete example, illustrate how the superleading logarithms arise, give numerical estimates and discuss some theoretical implications with respect to high energy QCD.

-  Jeudi 30 Novembre à 16h 30

Ana M. Teixeira (LPT, Orsay) : Hints on the SUSY seesaw from Lepton Flavour Violation

The study of lepton flavour violating processes (LFV) offers a unique tool to shed light on new physics. After introducing the main features of the scenario, we address the constraints on the seesaw parameters arising from the requirements of compatibility with low-energy data (neutrino masses and mixings, bounds on LFV decays and charged lepton electric dipole moments) and the imposition of a successful Baryon Asymmetry of the Universe via thermal leptogenesis. Finally, we consider hints on SUSY and seesaw parameters which can be derived from a potential measurement of low-energy neutrino mixings and LFV branching ratios.

-  Jeudi 23 Novembre à 10h 30 : SÉMINAIRE ANNULÉ

-  Mardi 21 Novembre à 16h 30

Domenico Falcone (Université de Naples) : Seesaw mechanism, quark-lepton symmetry and baryogenesis

A brief overview of the phenomenology related to the seesaw mechanism and the baryogenesis via leptogenesis is presented, assuming quark-lepton symmetry. In particular, it is explained how large but not maximal lepton mixing can be achieved within the type II seesaw mechanism. Moreover, the consequence for leptogenesis are explored, including flavor effects.

-  Jeudi 9 Novembre à 16h30

Eduardo Souza Fraga (Univ. Federal do Rio de Janeiro) : Langevin Dynamics of Chiral Fields and Polyakov Loops

We discuss the Langevin dynamics of phase conversion for the chiral and the deconfinement transitions in QCD with two flavors of massless quarks. Using the Linear Sigma Model and the Polyakov Loop Model, we investigate the role played by dissipation and noise in the time evolution of the chiral condensate and the condensate for the Polyakov loop. Effects from inhomogeneities and memory, as well as the interplay between the two phase transitions and possible implications for the phenomenology of high-energy heavy ion collisions, are also discussed.

-  Jeudi 19 octobre à 16h30

Prof. Rohini GODBOLE (IISC Bangalore) : CP violation in Supersymmetry and the Higgs sector

We discuss CP violation in the Minimal Supersymmetric extension of the Standard Model with specific attention to the Higgs sector. We propose new strategies to search for a light neutral Higgs boson which could have escaped detection at LEP and will not be accessible in the standard detection channels at both the Tevatron and LHC. We further outline possible ways of probing the CP mixing in the Higgs sector at future colliders.

-  Jeudi 5 octobre à 16h30

Rajiv V. Gavai (Tata Institute (TIFR), Mumbai) : Hadronic Screening Lengths : A window to Quark-Gluon Plasma

The debate on the nature of the quark-gluon plasma (QGP) has been brought into a sharp focus by the recent data from RHIC at BNL, New York. New models/scenarios have been proposed to explain their features, Lattice QCD can contribute to this debate by providing information of the properties of QGP. After a brief review of what has been achieved so far, I shall present our results on the hadronic screening lengths as another window to glean the properties of QGP.

-  Jeudi 28 septembre à 16h 30

Alexander Turbiner (Nuclear Science Institute, UNAM, Mexico) : Coulomb Systems in a Strong Magnetic Field and Atmosphere of a Neutron Star

Overview of one-two electron molecular systems made out of protons and/or $\alpha$-particles in a strong magnetic field $B > 10^9$\,G is presented. It is revealed very rich and unexpected physics. A particular emphasis is given to the one-electron exotic ions $H_3^++ (pppe), He_2^3+ (\alpha \alpha e)$ and to two-electron ions $H_3^+ (pppee), He_2^++ (\alpha \alpha ee)$. A description of recently observed absorption features in the spectra of the neutron star 1209 is given

Quantitative studies in a strong magnetic field are very complicated technically. Novel approach to the few-electron Coulomb systems in magnetic field, which provides very accurate results, based on variational calculus with physically relevant trial functions is briefly described. In particular, for $H_2$-molecule it leads to the most accurate trial function among known few-parametric trial functions.

-  Mardi 26 septembre à 16h 30

A. Abada, D. Becirevic , I. Mambrini, L. Oliver : Les highligths de la conférence ICHEP-2006 à Moscou