924 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.
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
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
Higher Twist Distribution Amplitudes of the Nucleon in QCD
We present the first systematic study of higher-twist light-cone distribution
amplitudes of the nucleon in QCD. We find that the valence three-quark state is
described at small transverse separations by eight independent distribution
amplitudes. One of them is leading twist-3, three distributions are twist-4 and
twist-5, respectively, and one is twist-6. A complete set of distribution
amplitudes is constructed, which satisfies equations of motion and constraints
that follow from conformal expansion. Nonperturbative input parameters are
estimated from QCD sum rules.Comment: 29 pages, 4 figures, eqn in (3.19) corrected, table 3 accordingly
changed, some typos fixe
Next-to-leading-order corrections to exclusive processes in factorization
We calculate next-to-leading-order (NLO) corrections to exclusive processes
in factorization theorem, taking as an example.
Partons off-shell by are considered in both the quark diagrams from
full QCD and the effective diagrams for the pion wave function. The gauge
dependences in the above two sets of diagrams cancel, when deriving the
-dependent hard kernel as their difference. The gauge invariance of the
hard kernel is then proven to all orders by induction. The light-cone
singularities in the -dependent pion wave function are regularized by
rotating the Wilson lines away from the light cone. This regularization
introduces a factorization-scheme dependence into the hard kernel, which can be
minimized in the standard way. Both the large double logarithms and
, being a parton momentum fraction, arise from the loop correction
to the virtual photon vertex, the former being absorbed into the pion wave
function and organized by the resummation, and the latter absorbed into a
jet function and organized by the threshold resummation. The NLO corrections
are found to be only few-percent for , if setting the
factorization scale to the momentum transfer from the virtual photon.Comment: 13 pages; version to appear in Physical Review
Leading-twist pion and kaon distribution amplitudes in the gauge-invariant nonlocal chiral quark model from the instanton vacuum
We investigate the leading-twist light-cone distribution amplitudes for the
pion and kaon based on the gauge-invariant nonlocal chiral quark model from the
instanton vacuum in the presence of external axial-vector currents. We find
that the nonlocal contribution from the gauge invariance has much effects on
the pion distribution amplitudes, while it changes mildly the kaon ones. We
also study the Gegenbauer moments of the distribution amplitudes and compare
them with the empirical analysis of the CLEO data.Comment: 14 pages, 10 figure
Periodic and Quasi-Periodic Compensation Strategies of Extreme Outages caused by Polarization Mode Dispersion and Amplifier Noise
Effect of birefringent disorder on the Bit Error Rate (BER) in an optical
fiber telecommunication system subject to amplifier noise may lead to extreme
outages, related to anomalously large values of BER. We analyze the Probability
Distribution Function (PDF) of BER for various strategies of Polarization Mode
Dispersion (PMD) compensation. A compensation method is proposed that is
capable of more efficient extreme outages suppression, which leads to
substantial improvement of the fiber system performance.Comment: 3 pages, 1 figure, Submitted to IEEE Photonics Letter
Leading twist contribution to color singlet decays
In this paper the leading twist contribution to
decays in the color singlet approximation is considered. It is shown, that the
predictions for \Br(\chi_0\to\omega\omega) is in a good agreement with the
experimental data, while \Br(\chi_{c2}\to\omega\omega) differs from the
experiment significantly.Comment: 4 pages, RevTeX; minor changes, some refrences adde
On the Quantum Jarzynski Identity
In this note, we will discuss how to compactly express and prove the
Jarzynski identity for an open quantum system with dissipative dynamics. We
will avoid explicitly measuring the work directly, which is tantamount to
continuously monitoring the system, and instead measure the heat flow from the
environment. We represent the measurement of heat flow with Hermitian map
superoperators that act on the system density matrix. Hermitian maps provide a
convenient and compact representation of sequential measurement and correlation
functions.Comment: 4 page
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
- …