119387058
Nonleptonic charmless 2-body B decays in the perturbative QCD approach
With the generalized factorization approximation, we calculate the branching ratios and $\mathrm{CP}$ asymmetries in B meson decays into two charmless pseudoscalar mesons. We give a new estimation of the matrix elements of $(S+P)(S\ensuremath{-}P)$ current products with the perturbative QCD method instead of the equation of motion. We find that our results are comparatively smaller than those in the literature.
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.
15449960
QCD Factorization For B Decays To Two Light Pseudoscalars Including Chirally Enhanced Corrections
Since b quark mass is not asymptotically large, chirally enhanced corrections which arise from twist-3 wave functions may be important in B decays. We thus evaluate the hadronic matrix elements with the emitted meson described by leading twist and twist-3 distribution amplitudes $\Phi_p(x)$. After summing over the four "vertex correction" diagrams, we obtain the results with infrared finiteness which shows that chirally enhanced corrections arise from $\Phi_p(x)$ can be consistently included in QCD factorization. We also briefly discuss the contributions from "hard spectator" diagrams.
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.
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.
119112269
Probing W+W−γ production and anomalous quartic gauge boson couplings at the CERN LHC
A bstractTriple gauge boson associated production at the LHC serves as an interesting channel to test the robustness of the Standard Model. Any deviation from its SM prediction may indicate possible existence of relevant new physics, e.g., anomalous quartic gauge boson couplings. In this paper, a Monte-Carlo feasibility study of measuring W+W−γ production with pure leptonic decays and probing anomalous quartic gauge-boson (e.g., WWγγ) couplings, is presented in detail for the first time, with parton shower and detector simulation effects taken into account. Our results show that at the $ \sqrt{s}=14 $ TeV LHC with an integrated luminosity of 100 (30) fb−1, one can reach a significance of 9 (5) σ to observe the SM W+W−γ production, and can constrain at the 95% C.L. the anomalous WWγγ coupling parameters, e.g., $ a{{{_{0,c}^W}} \left/ {{{\varLambda^2}}} \right.} $ (see ref. [16] for their definitions), at 1 × 10−5 GeV−2 level, respectively.