662 research outputs found
Decay Constants and Semileptonic Form Factors of Pseudoscalar Mesons
A relativistic constituent quark model is adopted to give an unified
description of the leptonic and semileptonic decays of pseudoscalar mesons
(\pi, K, D, D_s, B, B_s). The calculated leptonic decay constants and form
factors are found to be in good agreement with available experimental data and
the results of other approaches. Eventually, the model is found to reproduce
the scaling behaviours of spin-flavor symmetry in the heavy-quark limit.Comment: 5 pages LaTeX; based on talk given at the "QFTHEP '99 Workshop",
Moscow, May 27- June 2, 199
The semileptonic form factors of B and D mesons in the Quark Confinement Model
The form factors of the weak currents, which appear in the semileptonic
decays of the heavy pseudoscalar mesons, are calculated within the quark
confinement model by taking into account, for the first time, the structure of
heavy meson vertex and the finite quark mass contribution in the heavy quark
propagators. The results are in quite good agreement with the experimental
data.Comment: 12 pages LaTeX (elsart.sty) + 3 figure
A Positive Test for Fermi-Dirac Distributions of Quark-Partons
By describing a large class of deep inelastic processes with standard
parameterization for the different parton species, we check the characteristic
relationship dictated by Pauli principle: broader shapes for higher first
moments. Indeed, the ratios between the second and the first moment and the one
between the third and the second moment for the valence partons is an
increasing function of the first moment and agrees quantitatively with the
values found with Fermi-Dirac distributions.Comment: 15 pages LaTeX, 2 eps figures. Final version, to appear in Mod. Phys.
Lett.
A search for Z' in muon neutrino associated charm production
In many extensions of the Standard Model the presence of an extra neutral
boson, Z', is invoked. A precision study of weak neutral-current exchange
processes involving only second generation fermions is still missing. We
propose a search for Z' in muon neutrino associated charm production. This
process only involves Z' couplings with fermions from the second generation. An
experimental method is thoroughly described using an ideal detector. As an
application, the accuracy reachable with present and future experiments has
been estimated.Comment: 13 pages, 3 figures, late
Semileptonic and Rare -meson transitions in a QCD relativistic potential model
Using a QCD relativistic potential model, previously applied to the
calculation of the heavy meson leptonic constants, we evaluate the form factors
governing the exclusive decays , and . In our approach the heavy meson is described as a
bound state, whose wave function is solution of the relativistic Salpeter
equation, with an instantaneous potential displaying Coulombic behaviour at
small distances and linear behaviour at large distances. The light vector meson
is described by using a vector current interpolating field, according to the
Vector Meson Dominance assumption. A Pauli-Villars regularized propagator is
assumed for the quarks not constituting the heavy meson. Our procedure allows
to avoid the description of the light meson in terms of wave function and
constituent quarks, and consequently the problem of boosting the light meson
wave function.
Assuming as an input the experimental results on , we
evaluate all the form factors describing the semileptonic and
rare transitions. The overall comparison with the data, whenever available, is
satisfactory.Comment: Latex, 19 pages, 3 figure
Polarized Quarks, Gluons and Sea in Nucleon Structure Functions
We perform a NLO analysis of polarized deep inelastic scattering data to test
two different solutions to the so called spin crisis: one of them based on the
axial gluon anomaly and consistent with the Bjorken sum rule and another one,
where the defects in the spin sum rules and in the Gottfried sum rule are
related. In this case a defect is also expected for the Bjorken sum rule. The
first solution is slightly favoured by the SLAC E154 results, but both options
seem to be consistent with the CERN SMC data.Comment: 19 pages, LateX, 6 figures. Figures included in the tex
Statistical Inspired Parton Distributions and the Violation of QPM Sum Rules
A quantum statistical parametrization of parton distributions has been
considered. In this framework, the exclusion Pauli principle connects the
violation of the Gottfried sum rule with the Ellis and Jaffe one, and implies a
defect in the Bjorken sum rule. However, in terms of standard parametrizations
of the polarized distributions a good description of the data is obtained once
a large gluon polarization is provided. Interestingly, in this description
there is no violation of the Bjorken sum rule.Comment: 10 pages, LateX + 15 figures, Talk given at ``Hadrons 96'' Workshop,
Novy Svet (CRIMEA), June 9-1
Phenomenological Bounds on B to Light Semileptonic Form Factors
The form factors for the weak currents between B and light mesons are studied
by relating them to the corresponding D form factors at q^2_{max} according to
HQET, by evaluating them at q^2=0 by QCD sum rules, and by assuming a polar q^2
dependence. The results found are consistent with the information obtained from
exclusive non-leptonic two-body decays and, with the only exception of A_1,
with lattice calculations.Comment: 8 LaTeX pages + 2 figures. Will appear in Mod. Phys. Lett.
Semileptonic and rare B meson decays into a light pseudoscalar meson
In the framework of a QCD relativistic potential model we evaluate the form
factors describing the exclusive decays B => \pi l nu and B => K l+ l-. The
present calculation extends a previous analysis of B meson decays into light
vector mesons. We find results in agreement with the data, when available, and
with the theoretical constraints imposed by the Callan-Treiman relation and the
infinite heavy quark mass limit.Comment: 11 pages LaTeX + 2 figure
Coleman-Weinberg SO(10) GUT theories as inflationary models
The flat-space limit of the one-loop effective potential for SO(10) GUT theories in spatially flat Friedmann-Robertson-Walker cosmologies is applied to study the dynamics of the early universe. The numerical integration of the corresponding field equations shows that, for such grand unified theories, a sufficiently long inflationary stage is achieved for suitable choices of the initial conditions. However, a severe fine tuning of these initial conditions is necessary to obtain a large e-fold number. In the direction with residual symmetry SU(4)_{PS} \otimes SU(2)_{L} \otimes SU(2)_{R}, one eventually finds parametric resonance for suitable choices of the free parameters of the classical potential. This phenomenon leads in turn to the end of inflation
- …