240 research outputs found
Infrared Behavior of High-Temperature QCD
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
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
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
We realize the 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 . Our
realization coincides with those of Frenkel-Jing and Bernard when the level
takes the values 1 and 2 respectively.Comment: 8 pages, CRM-220
Pion Production from Baked-Alaska Disoriented Chiral Condensate
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
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
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>
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)
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 GeV in
which the cosmic baryon asymmetry originates from an initial asymmetry of an
anomalous -charge, and soft leptogenesis reembodies in -genesis.Comment: References updated. Some minor corrections to match the published
versio
Exclusive processes in position space and the pion distribution amplitude
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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