arXiv subjects
Publications and source records attributed to J. -M. Gerard.
The systematic large N_c limit within chiral perturbation provides an optimal eta-eta' mixing angle of about -27 degrees at leading order in p^2. In this frame, agreement with the data can be reached with higher order corrections of about 20%.
This review presents flavour related issues in the production and decays of heavy states at LHC, both from the experimental side and from the theoretical side. We review top quark physics and discuss flavour aspects of several extensions of the Standard Model, such as supersymmetry, little Higgs model or models with extra dimensions. This includes discovery aspects as well as measurement of several properties of these heavy states. We also present public available computational tools related to this topic.
In the Standard Model for electroweak interactions, the Higgs sector is known to display a "custodial" symmetry protecting the mass relation m_{W^\pm}^2=m_{W_3}^2 from large corrections. When considering extensions of the scalar sector, this symmetry has to be introduced by hand in order to pass current electroweak precision tests in a natural way. In this Letter we implement a generalized custodial symmetry in the two-Higgs-doublet model. Assuming the invariance of the potential under CP transformations, we prove the existence of a new custodial scenario characterized by m_{H^\pm}^2=m_{H^0}^2 instead of m_{H^\pm}^2=m_{A^0}^2. Consequently the pseudoscalar A^0 may be much lighter than the charged H^\pm, giving rise to interesting phenomenology.
We present an optical spectroscopy study of non-polar GaN/AlN quantum dots by time-resolved photoluminescence and by microphotoluminescence. Isolated quantum dots exhibit sharp emission lines, with linewidths in the 0.5-2 meV range due to spectral diffusion. Such linewidths are narrow enough to probe the inelastic coupling of acoustic phonons to confined carriers as a function of temperature. This study indicates that the carriers are laterally localized on a scale that is much smaller than the quantum dot size. This conclusion is further confirmed by the analysis of the decay time of the luminescence.
A Nordtvedt effect at cosmological scales affects the acoustic oscillations imprinted in the cosmic microwave background. The gravitational baryonic mass density of the universe is inferred at the first peak scale from WMAP data. The independent determination of the inertial baryonic mass density through the measurement of the deuterium abundance in the framework of standard big bang nucleosynthesis leads to a new constraint on a possible violation of the strong equivalence principle at the recombination time.
We estimate the density matrix element for the pi^0, eta and eta' production from the vacuum in the large-N_c limit. As a consequence, we find that the QCD axial anomaly leads to highly non-trivial corrections to the usual flavour SU(3) relations between B^0-> K^0 pi^0, B^0-> K^0 eta and B^0-> K^0 eta' decay amplitudes. These corrections may explain why the B-> K eta' branching ratio is about six times larger than the B-> K pi one.
The strongest constraint on Vtb presently comes from the 3 x 3 unitarity of the CKM matrix, which fixes Vtb to be very close to one. If the unitarity is relaxed, current information from top production at Tevatron still leaves open the possibility that Vtb is sizably smaller than one. In minimal extensions of the standard model with extra heavy quarks, the unitarity constraints are much weaker and the EW precision parameters entail the strongest bounds on Vtb. We discuss the experimental perspectives of discovering and identifying such new physics models at the Tevatron and the LHC, through a precise measurement of Vtb from the single top cross sections and by the study of processes where the extra heavy quarks are produced.
New data from neutrino oscillation experiments motivate us to extend a successful mass relation for the charged leptons to the other fundamental fermions. This new universal relation requires a Dirac mass around 3 10^-2 eV for the lightest neutrino and rules out a maximal atmospheric mixing. It also suggests a specific decomposition of the CKM mixing matrix.
We extend the simple scenario for $Ψ'$ decays suggested a few years ago. The $c\bar c$ pair in the $Ψ'$ does not annihilate directly into three gluons but rather survives before annihilating. An interesting prediction is that a large fraction of all $Ψ'$ decays could originate from the $Ψ' \to η_{c} (3π)$ channel which we urge experimentalists to identify. Our model solves the problem of the apparent hadronic excess in $Ψ'$ decays as well as the $ρπ$ puzzle since, in our view, the two-body decays of the $Ψ'$ are naturally of electromagnetic origin. Further tests of this picture are proposed, e.g. $J/Ψ\to b_{1}η$.
We reconcile the 1/N_c expansion with the observed eta-eta' mass spectrum. The chiral corrections introduced for that purpose are natural and consistent with the octet-singlet mixing angle theta=-(22\pm 1)^{\circ} extracted from phenomenology in the large N_c limit.
We study the effect of a violation of the strong equivalence principle (SEP) on the cosmic microwave background (CMB). Such a violation would modify the weight of baryons in the primordial gravitational potentials and hence their impact in the establishment of the photon-baryon plasma acoustic oscillations before recombination. This cosmological Nordtvedt effect alters the odd peaks height of the CMB temperature anisotropy power spectrum. A gravitational baryonic mass density of the universe may already be inferred at the first peak scale from the analysis of WMAP data. Experimental constraints on a primordial SEP violation are derived from a comparison with the universe's inertial baryonic mass density measured either in a full analysis of the CMB, or in the framework of the standard big bang nucleosynthesis (BBN).
We consider the flavour-changing operators associated with the strong axial and trace anomalies. Their short-distance generation through penguin-like diagrams is obtained within the QCD external field formalism. Standard-model operator evolution exhibits a suppression of anomalous effects in K and B hadronic weak decays. A genuine set of dimension-eight Delta S = 1 operators is also displayed.
A Regge model calculation relates the strong phase in $B \to DK$ to that in $B\to Dπ$. This provides a significant test of a hadronic picture of final state interactions in B decays.
The possibility of achieving a gauge coupling grand unification by increasing the QCD degrees of freedom at higher energies is investigated. When confronted with precision low-energy data, the generic weak-mixing angle relation sin^2(theta_W) = N/2(N+1) requires N=7 colors at the GUT scale M_U ~ 10^17 GeV. With the exclusive addition of light Higgs doublets to the standard model particle content, such a unification may also occur if N=5 at M_U ~ 10^16 GeV.
In this work, we have investigated the optical properties of two samples of CdSe quantum dots by using submicro-photoluminescence spectroscopy. The effect of vicinal-surface GaAs substrates on their properties has been also assessed. The thinner sample, grown on a substrate with vicinal surface, includes only dots with a diameter of less than 10 nm (type A islands). Islands of an average diameter of about 16 nm (type B islands) that are related to a phase transition via a Stranski-Krastanow growth process are also distributed in the thicker sample grown on an oriented substrate. We have studied the evolution of lineshapes of PL spectra for these two samples by improving spatial resolution that was achieved using nanoapertures or mesa structures. It was found that the use of a substrate with the vicinal surface leads to the suppression of excitonic PL emitted from a wetting layer.
We investigate the possibility of generating sizeable dipole radiations in relativistic theories of gravity. Optimal parameters to observe their effects through the orbital period decay of binary star systems are discussed. Constraints on gravitational couplings beyond general relativity are derived.
Trace Anomaly Dominance in weak $K$-decays successfully reproduces the $ΔI = {1\over 2}$ selection rule results, as observed in $K_S \to ππ, K_L \to πππ, K_S \to γγ$ and $K_L \to π^0 γγ$.
The physical deflection angle of a light ray propagating in a space-time supplied with an asymptotically flat metric has to be expressed in terms of the impact parameter.