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Performing a global fit of the experimental branching ratios and CP asymmetries of the charmless B ! PV decays according to QCD factorization, we find it impossible to reach a satisfactory agreement, the confidence level (CL) of the best fit being smaller than 0.1%. The main reason for this failure is the difficulty to accomodate several large experimental branching ratios of the strange channels. Furthermore, experiment was not able to exclude a large direct CP asymmetry in $\overline {B°}\rightarrow gamma+pi−, which is predicted very small by QCD factorisation. Then, trying a fit with QCD factorisation complemented by a charming-penguin inspired model, we reach a best fit which is not excluded by experiment (CL of about 8%) but is not fully convincing. These negative results must be tempered by the remark that some of the experimenta...
We study the impact of flavour in thermal leptogenesis, including the quantum oscillations of the asymmetries in lepton flavour space. In the Boltzmann equations we find different numerical factors and additional terms which can affect the results significantly. The upper bound on the CP asymmetry in a specific flavour is weaker than the bound on the sum. This suggests that -- when flavour dynamics is included -- there is no model-independent limit on the light neutrino mass scale,and that the lower bound on the reheat temperature is relaxed by a factor ~ (3 - 10).
The interpretation of experimental results at RHIC and in the future also at LHC requires very reliable and realistic models. Considerable effort has been devoted to the development of such models during the past decade, many of them being heavily used in order to analyze data. There are, however, serious inconsistencies in the above-mentioned approaches. In this paper, we will introduce a fully self-consistent formulation of the multiple-scattering scheme in the framework of a Gribov-Regge type effective theory.
We underline a problem existing in the heavy quark limit of QCD concerning the rates of semileptonic B decays into P-wave $D_J(j)$ mesons, where $j = {1 \\over 2}$ (wide states) or $j = {3 \\over 2}$ (narrow states). The leading order sum rules of Bjorken and Uraltsev suggest $\\Gamma [ \\bar{B} \\to D_{0,1} ({1 \\over 2}) \\ell \\nu ] \\ll \\Gamma [ \\bar{B} \\to D_{1,2} ({3 \\over 2}) \\ell \\nu ]$, in contradiction with experiment. The same trend follows also from a sum rule for the subleading $1/m_Q$ curent matrix element correction $\\xi_3(1)$. The problem is made explicit in relativistic quarks models \à la Bakamjian and Thomas, that give a transparent physical interpretation of the latter as due, not to a $L \\cdot S$ force, but to the Wigner rotation of the light quark spin. We point out moreover that the selection rule for dec...
We show that the sum rule recently proved by Uraltsev in the heavy quark limit of QCD holds in relativistic quark models \à la Bakamjian and Thomas, that were already shown to satisfy Isgur-Wise scaling and Bjorken sum rule. This new sum rule provides a {\\it rationale} for the lower bound of the slope of the elastic IW function $\\rho^2 \\geq {3 \\over 4}$ obtained within the BT formalism some years ago. Uraltsev sum rule suggests an inequality $|\\tau_{3/2}(1)| > |\\tau_{1/2}(1)|$. This difference is interpreted in the BT formalism as due to the Wigner rotation of the light quark spin, independently of a possible LS force. In BT models, the sum rule convergence is very fast, the $n = 0$ state giving the essential contribution in most of the phenomenological potential models. We underline that there is a serious problem, in the heavy ...
We revisit the determination of alpha_s(m_tau) using a fit to inclusive tau hadronic spectral moments in light of (1) the recent calculation of the fourth-order perturbative coefficient K_4 in the expansion of the Adler function, (2) new precision measurements from BABAR of e+e- annihilation cross sections, which decrease the uncertainty in the separation of vector and axial-vector spectral functions, and (3) improved results from BABAR and Belle on tau branching fractions involving kaons. We estimate that the fourth-order perturbative prediction reduces the theoretical uncertainty, introduced by the truncation of the series, by 20% with respect to earlier determinations. We discuss to some detail the perturbative prediction and show that the effect of the incomplete knowledge of the series is reduced by using the so-called contour-imp...
We present a detailed phenomenological study of direct photon production in association with a heavy-quark jet in pA collisions at the Relativistic Heavy Ion Collider (RHIC) and at the Large Hadron Collider (LHC) at next-to-leading order in QCD. The dominant contribution to the cross-section comes from the gluon--heavy-quark (gQ) initiated subprocess, making \gamma + Q production a process very sensitive to both the gluon and the heavy-quark parton distribution functions (PDFs). Additionally, the RHIC and LHC experiments are probing complementary kinematic regions in the momentum fraction x_2 carried by the target partons. Thus, the nuclear production ratio R^{\gamma+Q}_{pA} can provide strong constraints, over a broad x-range, on the poorly determined nuclear parton distribution functions which are extremely important for the interpre...
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