240 research outputs found

    Infrared Behavior of High-Temperature QCD

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    The damping rate \gamma_t(p) of on-shell transverse gluons with ultrasoft momentum p is calculated in the context of next-to-leading-order hard-thermal-loop-summed perturbation of high-temperature QCD. It is obtained in an expansion to second order in p. The first coefficient is recovered but that of order p^2 is found divergent in the infrared. Divergences from light-like momenta do also occur but are circumvented. Our result and method are critically discussed, particularly regarding a Ward identity obtained in the literature. When enforcing the equality between \gamma_t(0) and \gamma_l(0), a rough estimate of the magnetic mass is obtained. Carrying a similar calculation in the context of scalar quantum electrodynamics shows that the early ultrasoft-momentum expansion we make has little to do with the infrared sensitivity of the result.Comment: REVTEX4, 55 page

    Decays of Heavy Mesons

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    We present preliminary results for heavy to light transitions of pseudoscalar mesons, induced by the vector and tensor operators. This lattice study is performed in quenched approximation, by using the nonperturbatively improved Wilson action and operators. We also update the values of the heavy-light meson decay constants.Comment: LATT99(Heavy Quarks), 3 pages, 2 figure

    Heavy --> Light semileptonic decays of pseudoscalar mesons from lattice QCD

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    We have computed the form factors for B --> pi and D --> K(pi) semileptonic decays on the lattice by using full non-perturbative O(a) improvement, in the quenched approximation. Our results are expressed in terms of few parameters which describe the q^2-dependence and normalization of the form factors.Comment: 28 pages (LaTeX2e), 11 PostScript figures (version to appear in Nucl.Phys.B

    On a Bosonic-Parafermionic Realization of Uq(sl(2)^)U_q(\widehat{sl(2)})

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    We realize the Uq(sl(2)^)U_q(\widehat{sl(2)}) current algebra at arbitrary level in terms of one deformed free bosonic field and a pair of deformed parafermionic fields. It is shown that the operator product expansions of these parafermionic fields involve an infinite number of simple poles and simple zeros, which then condensate to form a branch cut in the classical limit q→1q\rightarrow 1. Our realization coincides with those of Frenkel-Jing and Bernard when the level kk takes the values 1 and 2 respectively.Comment: 8 pages, CRM-220

    Pion Production from Baked-Alaska Disoriented Chiral Condensate

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    We study the various stages of the evolution of chiral condensates disoriented via the ``baked-alaska'' mechanism, in which the condensates are described as the products of external sources localized on the light cone. Our analysis is based on the classical equations of motion of either the linear or the nonlinear sigma model. We use the associated framework of coherent states and, especially, their source functions to make the connection to the distribution functions for the produced particles. We also compare our classical approach with a mean-field calculation which includes a certain class of quantum corrections.Comment: replaced to correct misspelling of author's nam

    Hydrodynamical instabilities in an expanding quark gluon plasma

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    We study the mechanism responsible for the onset of instabilities in a chiral phase transition at nonzero temperature and baryon chemical potential. As a low-energy effective model, we consider an expanding relativistic plasma of quarks coupled to a chiral field, and obtain a phenomenological chiral hydrodynamics from a variational principle. Studying the dispersion relation for small fluctuations around equilibrium, we identify the role played by chiral waves and pressure waves in the generation of instabilities. We show that pressure modes become unstable earlier than chiral modes.Comment: 7 pages, 4 figure

    Heavy to Light Meson Exclusive Semileptonic Decays in Effective Field Theory of Heavy Quark

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    We present a general study on exclusive semileptonic decays of heavy (B, D, B_s) to light (pi, rho, K, K^*) mesons in the framework of effective field theory of heavy quark. Transition matrix elements of these decays can be systematically characterized by a set of wave functions which are independent of the heavy quark mass except for the implicit scale dependence. Form factors for all these decays are calculated consistently within the effective theory framework using the light cone sum rule method at the leading order of 1/m_Q expansion. The branching ratios of these decays are evaluated, and the heavy and light flavor symmetry breaking effects are investigated. We also give comparison of our results and the predictions from other approaches, among which are the relations proposed recently in the framework of large energy effective theory.Comment: 18 pages, ReVtex, 5 figures, added references and comparison of results, and corrected signs in some formula

    First Lattice Calculation of the Electromagnetic Operator Amplitude <pi0|Q+|K0>

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    We present the first lattice calculation of the matrix element of the electromagnetic operator , where Q+ = (Q_d e/16 pi^2)* (\bar s_L sigma{mu,nu} F{mu,nu} d_R + \bar s_R sigma{mu,nu} F{mu,nu} d_L). This matrix element plays an important role, since it contributes to enhance the CP violating part of the K_L -> pi0 e+ e- amplitude in supersymmetric extensions of the Standard Model.Comment: 12 pages, 3 figure

    Leptogenesis from Soft Supersymmetry Breaking (Soft Leptogenesis)

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    Soft leptogenesis is a scenario in which the cosmic baryon asymmetry is produced from a lepton asymmetry generated in the decays of heavy sneutrinos (the partners of the singlet neutrinos of the seesaw) and where the relevant sources of CP violation are the complex phases of soft supersymmetry-breaking terms. We explain the motivations for soft leptogenesis, and review its basic ingredients: the different CP-violating contributions, the crucial role played by thermal corrections, and the enhancement of the efficiency from lepton flavour effects. We also discuss the high temperature regime T>107T > 10^7 GeV in which the cosmic baryon asymmetry originates from an initial asymmetry of an anomalous RR-charge, and soft leptogenesis reembodies in RR-genesis.Comment: References updated. Some minor corrections to match the published versio

    Exclusive processes in position space and the pion distribution amplitude

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    We suggest to carry out lattice calculations of current correlators in position space, sandwiched between the vacuum and a hadron state (e.g. pion), in order to access hadronic light-cone distribution amplitudes (DAs). In this way the renormalization problem for composite lattice operators is avoided altogether, and the connection to the DA is done using perturbation theory in the continuum. As an example, the correlation function of two electromagnetic currents is calculated to the next-to-next-to-leading order accuracy in perturbation theory and including the twist-4 corrections. We argue that this strategy is fully competitive with direct lattice measurements of the moments of the DA, defined as matrix elements of local operators, and offers new insight in the space-time picture of hard exclusive reactions.Comment: 15 pages, 10 figure
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