733 research outputs found
Study of exclusive processes e^+ e^- \to VP
This paper is devoted to consideration of the hard exclusive processes
, where . Experimental measurement of
the cross section of the process at BaBar collaboration
at large center mass energy GeV and some low energy experimental
data GeV give us the possibility to study the cross section
in the broad energy region. As the result, we have determined the asymptotic
behavior of the cross section of in the limit , which is in agreement with perturbative QCD prediction. Assuming that
the same asymptotic behavior is valid for the other processes under
consideration and using low energy experimental data we have predicted the
cross sections of these processes at energies GeV. In
addition, we have calculated the cross sections of these processes at the same
energies within perturbative QCD. Our results are in agreement with available
experimental data.Comment: 10 pages, 2 tables, 6 figures; minor changes; article accepted to
publication is Phys. Rev.
Light Cone Sum Rules for gamma* N -> Delta Transition Form Factors
A theoretical framework is suggested for the calculation of gamma* N -> Delta
transition form factors using the light-cone sum rule approach. Leading-order
sum rules are derived and compared with the existing experimental data. We find
that the transition form factors in a several GeV region are dominated by the
``soft'' contributions that can be thought of as overlap integrals of the
valence components of the hadron wave functions. The ``minus'' components of
the quark fields contribute significantly to the result, which can be
reinterpreted as large contributions of the quark orbital angular momentumComment: 38 pages, 10 figures; some typos fixed and references added, to
appear in Phys. Rev.
Nucleon Form Factors to Next-to-Leading Order with Light-Cone Sum Rules
We have calculated the leading-twist next-to-leading order (NLO), i.e.,
O(alpha_s), correction to the light-cone sum-rules prediction for the
electromagnetic form factors of the nucleon. We have used the Ioffe nucleon
interpolation current and worked in M_N=0 approximation, with M_N being the
mass of the nucleon. In this approximation, only the Pauli form factor F_2
receives a correction and the calculated correction is quite sizable (cca 60%).
The numerical results for the proton form factors show the improved agreement
with the experimental data. We also discuss the problems encountered when going
away from M_N=0 approximation at NLO, as well as, gauge invariance of the
perturbative results. This work presents the first step towards the NLO
accuracy in the light-cone sum rules for baryon form factors.Comment: 68 pages, 9 figures; minor typos in the text corrected in accordance
with the published versio
A consistent model for \pi N transition distribution amplitudes and backward pion electroproduction
The extension of the concept of generalized parton distributions leads to the
introduction of baryon to meson transition distribution amplitudes (TDAs),
non-diagonal matrix elements of the nonlocal three quark operator between a
nucleon and a meson state. We present a general framework for modelling nucleon
to pion () TDAs. Our main tool is the spectral representation for \pi N
TDAs in terms of quadruple distributions. We propose a factorized Ansatz for
quadruple distributions with input from the soft-pion theorem for \pi N TDAs.
The spectral representation is complemented with a D-term like contribution
from the nucleon exchange in the cross channel. We then study backward pion
electroproduction in the QCD collinear factorization approach in which the
non-perturbative part of the amplitude involves \pi N TDAs. Within our two
component model for \pi N TDAs we update previous leading-twist estimates of
the unpolarized cross section. Finally, we compute the transverse target single
spin asymmetry as a function of skewness. We find it to be sizable in the
valence region and sensitive to the phenomenological input of our \pi N TDA
model.Comment: 39 pages, 9 figure
Parton content of the nucleon from distribution amplitudes and transition distribution amplitudes
The nucleon distribution amplitudes and the nucleon-to-pion transition
distribution amplitudes are investigated at leading twist within the frame of a
light-cone quark model. The distribution amplitudes probe the three-quark
component of the nucleon light-cone wave function, while higher order
components in the Fock-space expansion of the nucleon state are essential to
describe the nucleon-to-pion transition distribution amplitudes. Adopting a
meson-cloud model of the nucleon the nucleon-to-pion transition distribution
amplitudes are calculated for the first time.Comment: comments and references added; version to appear in Phys. Rev.
The Scalar and Form Factors in QCD
QCD sum rules on the light-cone are derived for the sum of the
and form factors taking into account contributions up to
twist four. Combining the results with the corresponding form factors
calculated previously by the same method, we obtain the scalar form factors
. Our sum rule predictions are compared with lattice results,
current-algebra constraints, and quark-model calculations. Furthermore, we
calculate decay distributions and the integrated width for the semileptonic
decay which is sensitive to . Finally, the
dependence of the sum rules on the heavy quark mass and the asymptotic scaling
laws are discussed.Comment: 19 pages, 10 figures, Latex, epsfi
Statistics of Entropy Production in Linearized Stochastic System
We consider a wide class of linear stochastic problems driven off the
equilibrium by a multiplicative asymmetric force. The force brakes detailed
balance, maintained otherwise, thus producing entropy. The large deviation
function of the entropy production in the system is calculated explicitly. The
general result is illustrated using an example of a polymer immersed in a
gradient flow and subject to thermal fluctuations.Comment: 4 pages, 1 figur
The Meson Light-Cone Distribution Amplitudes of Leading Twist Revisited
We give a complete re-analysis of the leading twist quark-antiquark
light-cone distribution amplitudes of longitudinal and transverse
mesons. We derive Wandzura-Wilczek type relations between different
distributions and update the coefficients in their conformal expansion using
QCD sum rules including next-to-leading order radiative corrections. We find
that the distribution amplitudes of quarks inside longitudinally and
transversely polarized mesons have a similar shape, which is in
contradiction to previous analyses.Comment: 21 pages, latex2e, requires a4wide.sty and epsf.sty, 6 PS figures
include
Scalar form factor of the nucleon and nucleon--scalar meson coupling constant in QCD
Scalar form factor of the nucleon is calculated in the framework of light
cone QCD sum rules, using the most general form of the baryon current. Using
the result on scalar form factor of the nucleon, the nucleon-scalar "sigma" and
"a_0" meson coupling constants are estimated. Our results on these couplings
are in good agreement with the prediction of the external field QCD sum rules
method.Comment: 20 pages, 12 figures, LaTeX formatte
Pion light cone wave function in the non-local NJL model
We use the simple instanton motivated NJL-type model to calculate the leading
twist pion light cone wave function. The model consists in employing the
momentum dependent quark mass in the quark loop entering the definition of the
wave function. The result is analytical up to a solution of a certain algebraic
equation. Various properties including the kT dependence of the pion wave
function are discussed. The resulting kT integrated wave function is not
asymptotic and is in agreement with recent analysis of the CLEO data.Comment: 9 pages, 12 figures, formulas (23-25) corrected, typos correcte
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