195 research outputs found
Analyses of decay constants and light-cone distribution amplitudes for s-wave heavy meson
In this paper, a study of light-cone distribution amplitudes (LCDAs) for
-wave heavy meson are presented in both general and heavy quark frameworks.
Within the light-front approach, the leading twist light-cone distribution
amplitudes, , and their relevant decay constants of heavy
pseudoscalar and vector mesons, , have simple relations. These relations
can be further simplified when the heavy quark limit is taken into
consideration. After fixing the parameters that appear in both Gaussian and
power-law wave functions, the corresponding decay constants are calculated and
compared with those of other theoretical approaches. The curves and the first
six -moments of are plotted and estimated. A conclusion is
drawn from these results: Even though the values of the decay constants of the
distinct mesons are almost equal, the curves of their LCDAs may have quite
large differences, and vice versa. Additionally, in the heavy quark limit, the
leading twist LCDAs, and , are compared
with the -meson LCDAs, , suggested by the other theoretical
groups.Comment: 25 pages, 3 figures, 4 tables, some typos are corrected, version to
be published in Phys. Rev.
Observations on the radiative corrections to pion beta-decay
We find that, in the local V-A theory, the radiative corrections to pion
beta-decay involving the weak vector current, when evaluated in the current
algebra (CA) formulation in which quarks are the fundamental underlying fields,
show a small difference with the more elementary calculations based directly on
the pion fields. We show that this difference arises from a specific
short-distance effect that depends on the algebra satisfied by the weak and
electromagnetic currents. On the other hand, we present a simple theoretical
argument that concludes that this difference does not occur when the CA
formulation is compared with the chiral perturbation theory (chiPT) approach.
Comparisons with previous studies, and with a more recent calculation based on
chiPT, are included. We also briefly review the important differences between
the results in the local V-A theory and the Standard Model.Comment: 5 pages, 1 figure. V2: two paragraphs have been added in Section III.
Final version on PR
Relation between Light Cone Distribution Amplitudes and Shape Function in B mesons
The Bakamjian-Thomas relativistic quark model provides a Poincar\'e
representation of bound states with a fixed number of constituents and, in the
heavy quark limit, form factors of currents satisfy covariance and Isgur-Wise
scaling. We compute the Light Cone Distribution Amplitudes of mesons
as well as the Shape Function , that enters
in the decay , that are also covariant in this class of
models. The LCDA and the SF are related through the quark model wave function.
The former satisfy, in the limit of vanishing constituent light quark mass, the
integral relation given by QCD in the valence sector of Fock space. Using a
gaussian wave function, the obtained is identical to the so-called
Roman Shape Function. From the parameters for the latter that fit the spectrum we predict the behaviour of . We
discuss the important role played by the constituent light quark mass. In
particular, although for vanishing light quark mass, a
non-vanishing mass implies the unfamiliar result . Moreover,
we incorporate the short distance behaviour of QCD to ,
which has sizeable effects at large . We obtain the values for the
parameters GeV and
GeV. We compare with other theoretical approaches and illustrate the
great variety of models found in the literature for the functions ; hence the necessity of imposing further constraints as in the
present paper. We briefly review also the different phenomena that are
sensitive to the LCDA.Comment: 6 figure
SU(3) symmetry breaking in decay constants and electromagnetic properties of pseudoscalar heavy mesons
In this paper, the decay constants and mean square radii of pseudoscalar
heavy mesons are studied in the SU(3) symmetry breaking. Within the light-front
framework, the ratios and are individually
estimated using the hyperfine splittings in the and
states and the light quark masses, (), to
extract the wave function parameter . The values and are obtained, which are not only
chiefly determined by the ratio of light quark masses , but also
insensitive to the heavy quark masses and the decay constants
. The dependence of on with the
varied charm quark masses is also shown. In addition, the mean square radii are
estimated as well. The values and are obtained, and the sensitivities of on
the heavy and light quark masses are similar to those of the decay constants.Comment: 21 pages, 5 figures, 4 tables, some typos are corrected, version to
be published in Phys. Rev.
Diffractive Higgs Production from Intrinsic Heavy Flavors in the Proton
We propose a novel mechanism for exclusive diffractive Higgs production in which the Higgs boson carries a significant fraction of the
projectile proton momentum. This mechanism will provide a clear experimental
signal for Higgs production due to the small background in this kinematic
region. The key assumption underlying our analysis is the presence of intrinsic
heavy flavor components of the proton bound state, whose existence at high
light-cone momentum fraction has growing experimental and theoretical
support. We also discuss the implications of this picture for exclusive
diffractive quarkonium and other channels.Comment: 30 pages, 5 figure
Twist-2 Light-Cone Pion Wave Function
We present an analysis of the existing constraints for the twist-2 light-cone
pion wave function. We find that existing information on the pion wave function
does not exclude the possibility that the pion wave function attains its
asymptotic form. New bounds on the parameters of the pion wave function are
presented.Comment: 7 pages, LaTeX, 1 PS-figure, one reference added, minor changes in
the tex
Resonant spin-dependent electron coupling in a III-V/II-VI heterovalent double quantum well
We report on design, fabrication, and magnetooptical studies of a III-V/II-VI
hybrid structure containing a GaAs/AlGaAs/ZnSe/ZnCdMnSe double quantum well
(QW). The structure design allows one to tune the QW levels into the resonance,
thus facilitating penetration of the electron wave function from the diluted
magnetic semiconductor ZnCdMnSe QW into the nonmagnetic GaAs QW and vice versa.
Magneto-photoluminescence studies demonstrate level anticrossing and strong
intermixing resulting in a drastic renormalization of the electron effective g
factor, in perfect agreement with the energy level calculations.Comment: 4 pages, 5 Postscript figures, uses revtex
A novel approach to light-front perturbation theory
We suggest a possible algorithm to calculate one-loop n-point functions
within a variant of light-front perturbation theory. The key ingredients are
the covariant Passarino-Veltman scheme and a surprising integration formula
that localises Feynman integrals at vanishing longitudinal momentum. The
resulting expressions are generalisations of Weinberg's infinite-momentum
results and are manifestly Lorentz invariant. For n = 2 and 3 we explicitly
show how to relate those to light-front integrals with standard energy
denominators. All expressions are rendered finite by means of transverse
dimensional regularisation.Comment: 10 pages, 5 figure
Study of Radiative Leptonic D Meson Decays
We study the radiative leptonic meson decays of D^+_{(s)}\to
\l^+\nu_{\l}\gamma (\l=e,\mu,\tau), and D^0\to
\l^+\l^-\gamma () within the light front quark model. In the standard
model, we find that the decay branching ratios of , and
are (), (), and
(), and that of D^0\to\l^+\l^-\gamma (\l=e,\mu) and
are and ,
respectively.Comment: 23 pages, 6 Figures, LaTex file, a reference added, to be published
in Mod. Phys. Lett.
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