**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.

**JOUR ET HEURE INHABITUELS**

**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.

**JOUR ET HEURE INHABITUELS**

**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.

**JOUR ET HEURE INHABITUELS**

**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

**SEMINAIRE ANNULE**

**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.