869 research outputs found
The spin structure of the nucleon in light-cone quark models
The quark spin densities related to generalized parton distributions in
impact-parameter space and to transverse-momentum dependent parton
distributions are reviewed within a light-cone quark model, with focus on the
role of the different spin-spin and spin-orbit correlations of quarks.Results
for azimuthal spin asymmetries in semi-inclusive deep-inelastic scattering due
to T-even transverse-momentum dependent parton distributions are also
discussed.Comment: proceedings of the workshop "Recent Advances in Perturbative QCD and
Hadronic Physics", 20-25 July 2009, ECT*, Trento (Italy), in Honor of Prof.
Anatoly Efremov's 75th Birthday Celebration; also based on the talk given at
the workshop "Transverse Partonic Structure of Hadrons", 21-26 June 2009,
Yerevan (Armenia); to appear in Mod. Phys. Lett.
Azimuthal spin asymmetries in light-cone constituent quark models
We present results for all leading-twist azimuthal spin asymmetries in
semi-inclusive lepton-nucleon deep-inelastic scattering due to T-even
transverse-momentum dependent parton distribution functions on the basis of a
light-cone constituent quark model. Attention is paid to discuss the range of
applicability of the model, especially with regard to the scale dependence of
the observables and the transverse-momentum dependence of the distributions. We
find good agreement with available experimental data and present predictions to
be further tested by future CLAS, COMPASS and HERMES data.Comment: 23 pages, 14 figures, 1 tabl
Nucleon magnetic moments in an extended chiral constituent quark model
We present results for the nucleon magnetic moments in the context of an
extended chiral constituent quark model based on the mechanism of the Goldstone
boson exchange, as suggested by the spontaneous breaking of chiral symmetry in
QCD. The electromagnetic charge-current operator is consistently deduced from
the model Hamiltonian, which includes all force components for the
pseudoscalar, vector and scalar meson exchanges. Thus, the continuity equation
is satisfied for each piece of the interaction, avoiding the introduction of
any further parameter. A good agreement with experimental values is found. The
role of isoscalar two-body operators, not constrained by the continuity
equation, is also investigated.Comment: 7 pages, 1 table, submitted for publication to Phys. Lett. B,
elsart.sty/elsart12.sty include
Transverse momentum dependent parton distributions and azimuthal asymmetries in light-cone quark models
We review the information on the spin and orbital angular momentum structure
of the nucleon encoded in the T-even transverse momentum dependent parton
distributions within light-cone quark models. Model results for azimuthal spin
asymmetries in semi-inclusive lepton-nucleon deep-inelastic scattering are
discussed, showing a good agreement with available experimental data and
providing predictions to be further tested by future CLAS, COMPASS and HERMES
data.Comment: 6 pages, 4 figures; proceedings of the "XIII Workshop On High Energy
Spin Physics Dubna Spin 2009", 1-5 September 2009, Dubna, Russi
TMDs and Azimuthal Spin Asymmetries in a Light-Cone Quark Model
The main properties of the leading-twist transverse momentum dependent parton
distributions in a light-cone constituent quark model of the nucleon are
reviewed, with focus on the role of the spin-spin and spin-orbit correlations
of quarks. Results for azimuthal single spin asymmetries in semi-inclusive deep
inelastic scattering are also discussed.Comment: Proceedings of SPIN2008, 6-11 October 2008, Charlottesville, VA, US
Charge-Exchange and multi-scattering effects in (e,e'n) knockout
Final-state interactions in (e,e'n) knockout reactions in the quasi-free
region are studied by considering the multistep direct scattering of the
ejectile nucleon. Primary and multiple particle emission are included within
the same model and are found to become important with increasing excitation
energy. Charge-exchange effects taken into account through the two-step
(e,e'p)(p,n) and three-step (e,e'p)(p,N)(N,n) processes are also found to
increase with energy. A comparison with the results obtained with an
isospin-dependent optical potential at small excitation energies is presented.Comment: 12 pages, 4 Postscript figures. A new section on multiple particle
emission added together with 2 new figures including primary and multiple
emission cross section
Transverse momentum dependent parton distributions in a light-cone quark model
The leading twist transverse momentum dependent parton distributions (TMDs)
are studied in a light-cone description of the nucleon where the Fock expansion
is truncated to consider only valence quarks. General analytic expressions are
derived in terms of the six amplitudes needed to describe the three-quark
sector of the nucleon light-cone wave function. Numerical calculations for the
T-even TMDs are presented in a light-cone constituent quark model, and the role
of the so-called pretzelosity is investigated to produce a nonspherical shape
of the nucleon.Comment: references added and typos corrected; version to appear in Phys. Rev.
Chiral-odd generalized parton distributions, transversity decomposition of angular momentum, and tensor charges of the nucleon
The forward limit of the chiral-odd generalized parton distributions (GPDs)
and their lower moments are investigated within the framework of the chiral
quark soliton model (CQSM), with particular emphasis upon the transversity
decomposition of nucleon angular momentum proposed by Burkardt. A strong
correlation between quark spin and orbital angular momentum inside the nucleon
is manifest itself in the derived second moment sum rule within the CQSM,
thereby providing with an additional support to the qualitative connection
between chiral-odd GPDs and the Boer-Mulders effects. We further confirm
isoscalar dominance of the corresponding first moment sum rule, which indicates
that the Boer-Mulders functions for the - and -quarks have roughly equal
magnitude with the same sign. Also made are some comments on the recent
empirical extraction of the tensor charges of the nucleon by Anselmino et al.
We demonstrate that a comparison of their result with any theoretical
predictions must be done with great care, in consideration of fairly strong
scale dependence of tensor charges, especially at lower renormalization scale.Comment: version to appear in Phys. Rev.
Dual modulation VCSEL-based sustainable transceiver for SSB DMT signals transmission
Single sideband DMT signal performance is analyzed in order to achieve high capacity and high spectral efficiency over 50-km uncompensated SMF. A sustainable implementation of the SSB DMT-based transceiver is proposed by means of a VCSEL source and a dual-modulator scheme, providing SSB without optical filtering and Hilbert transform implementation. Moreover, Kramers-Kronig detection, made possible by SSB, is studied at the receiver to effectively compensate the chromatic dispersion with direct detection
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