118635824
Jet quenching and holographic thermalization with a chemical potential
A bstractWe investigate jet quenching of virtual gluons and thermalization of a strongly-coupled plasma with a non-zero chemical potential via the gauge/gravity duality. By tracking a charged shell falling in an asymptotic AdSd+1 background for d = 3 and d = 4, which is characterized by the AdS-Reissner-Nordström-Vaidya (AdS-RN-Vaidya) geometry, we extract a thermalization time of the medium with a non-zero chemical potential. In addition, we study the falling string as the holographic dual of a virtual gluon in the AdS-RN-Vaidya spacetime. The stopping distance of the massless particle representing the tip of the falling string in such a spacetime could reveal the jet quenching of an energetic light probe traversing the medium in the presence of a chemical potential. We find that the stopping distance decreases when the chemical potential is increased in both AdS-RN and AdS-RN-Vaidya spacetimes, which correspond to the thermalized and thermalizing media respectively. Moreover, we find that the soft gluon with an energy comparable to the thermalization temperature and chemical potential in the medium travels further in the non-equilibrium plasma. The thermalization time obtained here by tracking a falling charged shell does not exhibit, generically, the same qualitative features as the one obtained studying non-local observables. This indicates that — holographically — the definition of thermalization time is observer dependent and there is no unambiguos definition.
54838095
Holographic photon production with magnetic field in anisotropic plasmas
A bstractWe investigate the thermal photon production from constant magnetic field in a strongly coupled and anisotropic plasma via the gauge/gravity duality. The dual geometry with pressure anisotropy is generated from the axion-dilaton gravity action introduced by Mateos and Trancancelli and the magnetic field is coupled to fundamental matters(quarks) through the D3/D7 embeddings. We find that the photon spectra with different quark mass are enhanced at large frequency when the photons are emitted parallel to the anisotropic direction with larger pressure or perpendicular to the magnetic field. However, in the opposite conditions for the emitted directions, the spectra approximately saturate isotropic results in the absence of magnetic field. On the other hand, a resonance emerges at moderate frequency for the photon spectrum with heavy quarks when the photons move perpendicular to the magnetic field. The resonance is more robust when the photons are polarized along the magnetic field. On the contrary, in the presence of pressure anisotropy, the resonance will be suppressed. There exist competing effects of magnetic field and pressure anisotropy on meson melting in the strongly coupled super Yang-Mills plasma, while we argue that the suppression led by anisotropy may not be applied to the quark gluon plasma.
119210077
Refactorizing NRQCD short-distance coefficients in exclusive quarkonium production
In a typical exclusive quarkonium production process, when the center-of-mass energy, is much greater than the heavy quark mass in, large kinematic logarithms of s/m(2) will unavoidably arise at each order of perturbative expansion in the short-distance coefficients of the nonrelativistic QCD (NRQCD) factorization formalism, which may potentially harm the perturbative expansion. This symptom reflects that the hard regime in NRQCD factorization is too coarse and should be further factorized. We suggest that this regime can be further separated into "hard" and "collinear" degrees of freedom, so that the familiar light-cone approach can be employed to reproduce the NRQCD matching coefficients at the zeroth order of m(2)/s and order by order in alpha(s). Taking two simple processes, exclusive eta(b)+ gamma production in e(+)e(-) annihilation and Higgs boson radiative decay into gamma, as examples, we illustrate how the leading logarithms of s/m(2) in the NRQCD matching coefficients are identified and summed to all orders in alpha(s) with the aid of Brodsky-Lepage evolution equation. (C) 2009 Elsevier B.V. All rights reserved.
11323590
Charmless two-body B decays: A global analysis with QCD factorization
In this paper, we perform a global analysis of $\stackrel{\ensuremath{\rightarrow}}{B}\mathrm{PP}$ and $\mathrm{PV}$ decays with the QCD factorization approach. It is encouraging to observe that the predictions of QCD factorization are in good agreement with experiment. The best fit $\ensuremath{\gamma}$ is around $79\ifmmode^\circ\else\textdegree\fi{}.$ The penguin-diagram--to--tree-diagram ratio $|{P}_{\ensuremath{\pi}\ensuremath{\pi}}{/T}_{\ensuremath{\pi}\ensuremath{\pi}}|$ of ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ decays is preferred to be larger than $0.3.$ We also show the confidence levels for some interesting channels: ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0},$ ${K}^{+}{K}^{\ensuremath{-}},$ and ${B}^{+}\ensuremath{\rightarrow}\ensuremath{\omega}{\ensuremath{\pi}}^{+},\ensuremath{\omega}{K}^{+}.$ For $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\pi}{K}^{*}$ decays, they are expected to have smaller branching ratios with more precise measurements.
118456126
Broken S3 flavor symmetry of leptons and quarks: Mass spectra and flavor mixing patterns
Abstract We apply the discrete S 3 flavor symmetry to both lepton and quark sectors of the Standard Model extended by introducing one Higgs triplet and realizing the type-II seesaw mechanism for finite neutrino masses. The resultant mass matrices of charged leptons ( M l ), neutrinos ( M ν ), up-type quarks ( M u ) and down-type quarks ( M d ) have a universal form consisting of two terms: one is proportional to the identity matrix I and the other is proportional to the democracy matrix D . We argue that the textures of M l , M u and M d are dominated by the D term, while that of M ν is dominated by the I term. This hypothesis implies a near mass degeneracy of three neutrinos and can naturally explain why the mass matrices of charged fermions are strongly hierarchical, why the quark mixing matrix is close to I and why the lepton mixing matrix contains two large angles. We discuss a rather simple perturbation ansatz to break the S 3 symmetry and obtain more realistic mass spectra of leptons and quarks as well as their flavor mixing patterns. We stress that the I term, which used to be ignored from M l , M u and M d , is actually important because it can significantly modify the smallest lepton flavor mixing angle θ 13 or three quark flavor mixing angles.