3,429 research outputs found
Endpoint behavior of the pion distribution amplitude in QCD sum rules with nonlocal condensates
Starting from the QCD sum rules with nonlocal condensates for the pion
distribution amplitude, we derive another sum rule for its derivative and its
"integral" derivatives---defined in this work. We use this new sum rule to
analyze the fine details of the pion distribution amplitude in the endpoint
region . The results for endpoint-suppressed and flat-top (or
flat-like) pion distribution amplitudes are compared with those we obtained
with differential sum rules by employing two different models for the
distribution of vacuum-quark virtualities. We determine the range of values of
the derivatives of the pion distribution amplitude and show that
endpoint-suppressed distribution amplitudes lie within this range, while those
with endpoint enhancement---flat-type or CZ-like---yield values outside this
range.Comment: 20 pages, 10 figures, 1 table, conclusions update
QCD vacuum tensor susceptibility and properties of transversely polarized mesons
We re-estimate the tensor susceptibility of QCD vacuum, , and to this
end, we re-estimate the leptonic decay constants for transversely polarized
- ,~- and b_1-mesons. The origin of the susceptibility is
analyzed using duality between - and b_1- channels in a 2-point
correlator of tensor currents. We confirm the results in Nucl.Phys.
B283(1987)706 for the 2-point correlator of tensor currents and disagree with
Phys.Lett. B395(1997)307 on both OPE expansion and the value of QCD vacuum
tensor susceptibility. Using our value for the latter we determine new
estimations of nucleon tensor charges related to the first moment of the
transverse structure function h_1 of a nucleon.Comment: 11 pages, LATeX2-eps, 1 Table, 2 figures are enclosed as ps-files,
psbox.tex is enclosed as a macros; a comparison with another approach and a
new reference are adde
New shapes of light-cone distributions of the transversely polarized \rho-mesons
We re-analyze the leading twist light-cone distributions for transversely
polarized \rho-, \rho'- and b_1-mesons in the framework of QCD sum rules with
nonlocal condensates. Using different kinds of sum rules to obtain reliable
predictions, we estimate the 2-, 4-, 6- and 8-th moments for transversely
polarized \rho- and \rho'-meson distributions and re-estimate tensor couplings
f^T_{\rho,\rho',b_1}. We stress that the results of standard sum rules also
support our estimation of the second moment of the transversely polarized
\rho-meson distribution. New models for light-cone distributions of these
mesons are constructed. Phenomenological consequences from these distributions
are briefly discussed. Our results are compared with those found by Ball and
Braun (1996), and the latter is shown to be incomplete.Comment: 18 pages, 7 figures use psbox-macro, 1 table, introduction is
improved, new (7) section with applications to semileptonic B->rho-decay is
added. to appear in Eur. Phys. J.
Nonlinear electromagnetic response of graphene: Frequency multiplication and the self-consistent-field effects
Graphene is a recently discovered carbon based material with unique physical
properties. This is a monolayer of graphite, and the two-dimensional electrons
and holes in it are described by the effective Dirac equation with a vanishing
effective mass. As a consequence, electromagnetic response of graphene is
predicted to be strongly non-linear. We develop a quasi-classical kinetic
theory of the non-linear electromagnetic response of graphene, taking into
account the self-consistent-field effects. Response of the system to both
harmonic and pulse excitation is considered. The frequency multiplication
effect, resulting from the non-linearity of the electromagnetic response, is
studied under realistic experimental conditions. The frequency up-conversion
efficiency is analysed as a function of the applied electric field and
parameters of the samples. Possible applications of graphene in terahertz
electronics are discussed.Comment: 14 pages, 7 figures, invited paper written for a special issue of
JPCM "Terahertz emitters
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