6,545 research outputs found
Semileptonic transition in three--point QCD sum rules and HQET with gluon condensate corrections
Taking into account the gluon condensate contributions, the form factors of
the semileptonic transition with are
calculated in the framework of the three point QCD sum rules. The heavy quark
effective theory limit of the form factors are also computed. The relevant
total decay width as well as the branching ratio are evaluated and compared
with the predictions of the other non-perturbative approaches.Comment: 27 Pages, 4 Figures and 4 Table
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.
Neutrino Induced Coherent Pion Production off Nuclei and PCAC
We review the Rein--Sehgal model and criticize its use for low energy
neutrino induced coherent pion production. We have studied the validity of the
main approximations implicit in that model, trying to compare with physical
observables when that is possible and with microscopical calculations. Next, we
have tried to elaborate a new improved model by removing the more problematic
approximations, while keeping the model still reasonably simple. Last, we have
discussed the limitations intrinsic to any approach based on the partial
conservation of the axial current hypothesis. In particular, we have shown the
inability of such models to determine the angular distribution of the outgoing
pion with respect to the direction of the incoming neutrino, except for the
kinematical point.Comment: 19 latex pages, 7 figures, 1 table. Version accepted for publication
in Physical Review
Decay constants of the heavy-light mesons from the field correlator method
Meson Green's functions and decay constants in different
channels are calculated using the Field Correlator Method. Both,
spectrum and , appear to be expressed only through universal
constants: the string tension , , and the pole quark masses.
For the -wave states the calculated masses agree with the experimental
numbers within MeV. For the and mesons the values of are equal to 210(10) and 260(10) MeV, respectively, and their ratio
=1.24(3) agrees with recent CLEO experiment. The values MeV are obtained for the , , and mesons
with the ratio =1.19(2) and =1.14(2). The decay constants
for the first radial excitations as well as the decay constants
in the vector channel are also calculated. The difference of
about 20% between and , and directly follows
from our analytical formulas.Comment: 37 pages, 10 tables, RevTeX
Two-particle decays of B_c meson into charmonium states
The factorization of hard and soft contributions into the hadronic decays of
B_c meson at large recoils is explored in order to evaluate the decay rates
into the S, P and D-wave charmonia associated with rho and pi. The constraints
of approach applicability and uncertainties of numerical estimates are
discussed. The mode with the J/psi in the final state is evaluated taking into
account the cascade radiative electromagnetic decays of excited P-wave states,
that enlarges the branching ratio by 20-25%.Comment: 13 pages, LaTeX axodraw-style, 1 figure, 2 table
The Field Theory of Gravitation and The Rest Mass of Particles
It is shown in this work that all free physical fields should have a nonzero
rest mass according to the field theory of gravitation.Comment: 4 page
Dynamical Model of Coherent Pion Production in Neutrino-Nucleus Scattering
We study coherent pion production in neutrino-nucleus scattering in the
energy region relevant to neutrino oscillation experiments of current interest.
Our approach is based on a combined use of the Sato-Lee model of electroweak
pion production on a nucleon and the Delta-hole model of pion-nucleus
reactions. Thus we develop a model which describes pion-nucleus scattering and
electroweak coherent pion production in a unified manner. Numerical
calculations are carried out for the case of the 12C target. All the free
parameters in our model are fixed by fitting to both total and elastic
differential cross sections for pi-12C scattering. Then we demonstrate the
reliability of our approach by confronting our prediction for the coherent pion
photo-productions with data. Finally, we calculate total and differential cross
sections for neutrino-induced coherent pion production, and some of the results
are (will be) compared with the recent (forthcoming) data from K2K, SciBooNE
and MiniBooNE. We also study effect of the non-locality of the
Delta-propagation in the nucleus, and compare the elementary amplitudes used in
different microscopic calculations.Comment: 42 pages, 21 figure
Breakdown of PCAC in diffractive neutrino interactions
We test the hypothesis of partially conserved axial current (PCAC) in high
energy diffractive neutrino production of pions. Since the pion pole
contribution to the Adler relation (AR) is forbidden by conservation of the
lepton current, the heavier states, like the a_1 pole, \rho-\pi-cut, etc.,
control the lifetime of the hadronic fluctuations of the neutrino. We evaluate
the deviation from the AR in diffractive neutrino-production of pions on proton
and nuclear targets. At high energies, when all the relevant time scales
considerably exceed the size of the target, the AR explicitly breaks down on an
absorptive target, such as a heavy nucleus. In this regime, close to the black
disc limit, the off-diagonal diffractive amplitudes vanish, while the diagonal
one, \pi->\pi, which enters the AR, maximizes and saturates the unitarity
bound. At lower energies, in the regime of short lifetime of heavy hadronic
fluctuations the AR is restored, i.e. it is not altered by the nuclear effects.Comment: 10 pages, 5 figure
A Comparative Study of within QCD Sum Rules with Two Typical Correlators up to Next-to-Leading Order
The B-decay constant is an important component for studying -meson
decays, which can be studied through QCD sum rules. We make a detailed
discussion on from two sum rules, i.e. sum rules I and II, which are
derived from the conventional correlator and the correlator with chiral
currents respectively. It is found that these two sum rules are consistent with
each other. However, the sum rules II has less uncertainty sources than that of
sum rules I, and then it can be more accurate if we know the dimension-four
gluon condensate well. It is found that decreases with the increment of
, and to compare with the Belle experimental data on , both sum rules
prefer smaller pole -quark mass, GeV. By varying all the
input parameters in their reasonable region and adding all the uncertainties
together in quadrature, we obtain MeV for sum rules I and
MeV for sum rules II.Comment: 11 pages, 4 figures, 2 tables. To match the printed version. To be
published in Communications in Theoretical Physic
Proportionate vs disproportionate distribution of wealth of two individuals in a tempered Paretian ensemble
We study the distribution P(\omega) of the random variable \omega = x_1/(x_1
+ x_2), where x_1 and x_2 are the wealths of two individuals selected at random
from the same tempered Paretian ensemble characterized by the distribution
\Psi(x) \sim \phi(x)/x^{1 + \alpha}, where \alpha > 0 is the Pareto index and
is the cut-off function. We consider two forms of \phi(x): a bounded
function \phi(x) = 1 for L \leq x \leq H, and zero otherwise, and a smooth
exponential function \phi(x) = \exp(-L/x - x/H). In both cases \Psi(x) has
moments of arbitrary order.
We show that, for \alpha > 1, P(\omega) always has a unimodal form and is
peaked at \omega = 1/2, so that most probably x_1 \approx x_2. For 0 < \alpha <
1 we observe a more complicated behavior which depends on the value of \delta =
L/H. In particular, for \delta < \delta_c - a certain threshold value -
P(\omega) has a three-modal (for a bounded \phi(x)) and a bimodal M-shape (for
an exponential \phi(x)) form which signifies that in such ensembles the wealths
x_1 and x_2 are disproportionately different.Comment: 9 pages, 8 figures, to appear in Physica
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