945 research outputs found
The leading-twist pion and kaon distribution amplitudes from the QCD instanton vacuum
We investigate the leading-twist light-cone distribution amplitudes for the
pion and kaon, based on the nonlocal chiral quark model from the instanton
vacuum. Effects of explicit flavor SU(3)-symmetry breaking are taken into
account. The Gegenbauer moments are computed, analyzed and compared with those
of other models. The one-loop QCD evolution of the moments is briefly
discussed. The transverse momentum distributions are also discussed for the
pion and kaon light-cone wave functions.Comment: 17 pages, 12 figures. Accepted for publication in Physical Review
Pion distribution amplitude from holographic QCD and the electromagnetic form factor F_pi(Q2)
The holographic QCD prediction for the pion distribution amplitude (DA)
is used to compute the pion spacelike electromagnetic form
factor within the QCD light-cone sum rule method. In
calculations the pion's renormalon-based model twist-4 DA, as well as the
asymptotic twist-4 DA are employed. Obtained theoretical predictions are
compared with experimental data and with results of the holographic QCD
Light Cone Sum Rules for the pi0-gamma*-gamma Form Factor Revisited
We provide a theoretical update of the calculations of the pi0-gamma*-gamma
form factor in the LCSR framework, including up to six polynomials in the
conformal expansion of the pion distribution amplitude and taking into account
twist-six corrections related to the photon emission at large distances. The
results are compared with the calculations of the B-> pi l nu decay and pion
electromagnetic form factors in the same framework. Our conclusion is that the
recent BaBar measurements of the pi0-gamma*-gamma form factor at large momentum
transfers are consistent with QCD, although they do suggest that the pion DA
may have more structure than usually assumed.Comment: 20 pages, 14 figures, 5 table
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.
Time-Dependent Quasiparticle Current Density Functional Theory of X-Ray Nonlinear Response Functions
A real-space representation of the current response of many-electron systems
with possible applications to x-ray nonlinear spectroscopy and magnetic
susceptibilities is developed. Closed expressions for the linear, quadratic and
third-order response functions are derived by solving the adiabatic Time
Dependent Current Density Functional (TDCDFT) equations for the single-electron
density matrix in Liouville space.Comment: 11 page
The eta-photon transition form factor
The eta-photon transition form factor is evaluated in a formalism based on a
phenomenological description at low values of the photon virtuality, and a
QCD-based description at high photon virtualities, matching at a scale
. The high photon virtuality description makes use of a Distribution
Amplitude calculated in the Nambu-Jona-Lasinio model with Pauli-Villars
regularization at the matching scale , and QCD evolution from
to higher values of . A good description of the available
data is obtained. The analysis indicates that the recent data from the BaBar
collaboration on pion and eta transition form factor can be well reproduced, if
a small contribution of twist three at the matching scale is
included.Comment: 14 pages, 3 figures, revised version, minor corrections, references
added, conclusions unchanged. Accepted for publication in Phys. Rev.
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
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.
QCD Calculation of the Form Factors
We calculate the form factors for the heavy-to-light transitions
by means of QCD sum rules using and light-cone
wave functions. Higher twist contributions as well as gluonic corrections are
taken into account. The sensitivity to the shape of the leading-twist wave
functions and effects of SU(3)-breaking are discussed. The results are compared
with quark model predictions and with the results from QCD sum rules for
three-point correlators.Comment: 13 pages +5 figures available upon request , LaTeX , CERN-TH.6880/93,
MPI-Ph/93-32, LMU-07/9
Kaon Distribution Amplitude from QCD Sum Rules
We present a new calculation of the first Gegenbauer moment of the
kaon light-cone distribution amplitude. This moment is determined by the
difference between the average momenta of strange and nonstrange valence quarks
in the kaon. To calculate , QCD sum rule for the diagonal correlation
function of local and nonlocal axial-vector currents is used. Contributions of
condensates up to dimension six are taken into account, including
-corrections to the quark-condensate term. We obtain
, differing by the sign and magnitude from the recent
sum-rule estimate from the nondiagonal correlation function of pseudoscalar and
axial-vector currents. We argue that the nondiagonal sum rule is numerically
not reliable. Furthermore, an independent indication for a positive is
given, based on the matching of two different light-cone sum rules for the
form factor. With the new interval of we update our previous
numerical predictions for SU(3)-violating effects in form
factors and charmless (B) decays.Comment: a comment and a reference added, version to appear in Phys.Rev.D, 17
pages, 7 figure
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