385 research outputs found
Accessing the Longitudinally Polarized Photon Content of the Proton
We investigate the QED Compton process (QEDCS) in longitudinally polarized
lepton-proton scattering both in the elastic and inelastic channels and show
that the cross section can be expressed in terms of the polarized equivalent
photon distribution of the proton. We provide the necessary kinematical
constraints to extract the polarized photon content of the proton using this
process at HERMES, COMPASS and eRHIC. We also discuss the suppression of the
major background process coming from virtual Compton scattering. We point out
that such an experiment can give valuable information on in the
small , broad region at the future polarized collider eRHIC and
especially in the lower , medium region in fixed target experiments.Comment: Version to appear in PR
Deeply Virtual Compton Scattering on nucleons and nuclei in generalized vector meson dominance model
We consider Deeply Virtual Compton Scattering (DVCS) on nucleons and nuclei
in the framework of generalized vector meson dominance (GVMD) model. We
demonstrate that the GVMD model provides a good description of the HERA data on
the dependence of the proton DVCS cross section on Q^2, W (at Q^2=4 GeV^2) and
t. At Q^2 = 8 GeV^2, the soft W-behavior of the GVMD model somewhat
underestimates the W-dependence of the DVCS cross section due to the hard
contribution not present in the GVMD model. We estimate 1/Q^2 power-suppressed
corrections to the DVCS amplitude and the DVCS cross section and find them
large. We also make predictions for the nuclear DVCS amplitude and cross
section in the kinematics of the future Electron-Ion Collider. We predict
significant nuclear shadowing, which matches well predictions of the
leading-twist nuclear shadowing in DIS on nuclei.Comment: 25 pages, 9 figures, 1 tabl
The solar wind from a stellar perspective: how do low-resolution data impact the determination of wind properties?
Alfv\'en-wave-driven 3D magnetohydrodynamic (MHD) models, which are
increasingly used to predict stellar wind properties, contain unconstrained
parameters and rely on low-resolution stellar magnetograms. We explore the
effects of the input Alfv\'en wave energy flux and the surface magnetogram on
the wind properties predicted by the Alfv\'en Wave Solar Model (AWSoM). We
lowered the resolution of two solar magnetograms during solar cycle maximum and
minimum using spherical harmonic decomposition. The Alfv\'en wave energy was
altered based on non-thermal velocities determined from a far ultraviolet (FUV)
spectrum of the solar twin 18 Sco. Additionally, low-resolution magnetograms of
three solar analogues were obtained using Zeeman Doppler imaging (ZDI).
Finally, the simulated wind properties were compared to Advanced Composition
Explorer (ACE) observations. AWSoM simulations using well constrained input
parameters taken from solar observations can reproduce the observed solar wind
mass and angular momentum loss rates. The resolution of the magnetogram has a
small impact on the wind properties and only during cycle maximum. However,
variation in Alfv\'en wave energy influences the wind properties irrespective
of the solar cycle activity level. Furthermore, solar wind simulations carried
out using the low-resolution magnetogram of the three stars instead of the
solar magnetogram could lead to an order of a magnitude difference in the
simulated wind properties. The choice in Alfv\'en energy has a stronger
influence on the wind output compared to the magnetogram resolution. The
influence could be even stronger for stars whose input boundary conditions are
not as well constrained as those of the Sun. Unsurprisingly, replacing the
solar magnetogram with a stellar magnetogram could lead to completely
inaccurate solar wind properties, and should be avoided in solar and stellar
wind simulations.Comment: accepted for publication in A&
DVCS on spinless nuclear targets in impulse approximation
Within the impulse approximation, we derive expressions for the amplitude of
deeply virtual Compton scattering on spinless nuclei in terms of the
generalized parton distributions of the nucleon. As an application, nuclear
effects in the beam-charge and single-spin asymmetries are discussed.Comment: 13 pages, 2 figures, Late
Two-hadron semi-inclusive production including subleading twist
We extend the analysis of two-hadron fragmentation functions to the
subleading twist, discussing also the issue of color gauge invariance. Our
results can be used anywhere two unpolarized hadrons are semi-inclusively
produced in the same fragmentation region, also at moderate values of the hard
scale Q. Here, we consider the example of polarized deep-inelastic production
of two hadrons and we give a complete list of cross sections and spin
asymmetries up to subleading twist. Among the results, we highlight the
possibility of extracting the transversity distribution with longitudinally
polarized targets and also the twist-3 distribution e(x), which is related to
the pion-nucleon sigma term and to the strangeness content of the nucleon.Comment: 16 pages, RevTeX4, 5 figures, revised notation of several formulae,
added text in Secs. III-V, added reference
Role of the Delta (1232) in DIS on polarized He and extraction of the neutron spin structure function
We consider the effect of the transitions and in deep inelastic scattering on polarized He on the extraction
of the neutron spin structure function . Making the natural
assumption that these transitions are the dominant non-nucleonic contributions
to the renormalization of the axial vector coupling constant in the A=3 system,
we find that the effect of increases by % in the range , where our considerations are applicable
and most of the data for exist.Comment: 23 pages, 6 figures, revte
Nuclear shadowing in polarized DIS on ^6LiD at small x and its effect on the extraction of the deuteron spin structure function g_{1}^{d}(x,Q^2)
We consider the effect of nuclear shadowing in polarized deep inelastic
scattering (DIS) on ^6LiD at small Bjorken x and its relevance to the
extraction of the deuteron spin structure function g_{1}^{d}(x,Q^2). Using
models, which describe nuclear shadowing in unpolarized DIS, we demonstrate
that the nuclear shadowing correction to g_{1}^{d}(x,Q^2) is significant.Comment: 17 pages, 2 figure
Polynomiality of unpolarized off-forward distribution functions and the D-term in the chiral quark-soliton model
Mellin moments of off-forward distribution functions are even polynomials of
the skewedness parameter. This constraint, called polynomiality property,
follows from Lorentz- and time-reversal invariance. We prove that the
unpolarized off-forward distribution functions in the chiral quark-soliton
model satisfy the polynomiality property. The proof is an important
contribution to the demonstration that the description of off-forward
distribution functions in the model is consistent. As a byproduct of the proof
we derive explicit model expressions for moments of the D-term and compute the
first coefficient in the Gegenbauer expansion for this term.Comment: 18 pages, no figures. Corrections and improvements in section 6. To
appear in Phys.Rev.
Higher moments of nucleon spin structure functions in heavy baryon chiral perturbation theory and in a resonance model
The third moment of the twist-3 part of the nucleon spin structure
function is generalized to arbitrary momentum transfer and is
evaluated in heavy baryon chiral perturbation theory (HBChPT) up to order
and in a unitary isobar model (MAID). We show how to link
as well as higher moments of the nucleon spin structure functions
and to nucleon spin polarizabilities. We compare our results with the
most recent experimental data, and find a good description of these available
data within the unitary isobar model. We proceed to extract the twist-4 matrix
element which appears in the suppressed term in the twist
expansion of the spin structure function for proton and neutron.Comment: 30 pages, 7 figure
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