351 research outputs found
Charge Symmetry Violation Corrections to Determination of the Weinberg Angle in Neutrino Reactions
We show that the correction to the Paschos-Wolfenstein relation associated
with charge symmetry violation in the valence quark distributions is
essentially model independent. It is proportional to a ratio of quark momenta
that is independent of Q^2. This result provides a natural explanation of the
surprisingly good agreement found between our earlier estimates within several
different models. When applied to the recent NuTeV measurement, this effect
significantly reduces the discrepancy with other determinations of the Weinberg
angle.Comment: 7 pages, no figures; expanded discussion of N.ne.Z correction
Color Magnetic Corrections to Quark Model Valence Distributions
We calculate order color magnetic corrections to the valence quark
distributions of the proton using the Los Alamos Model Potential wavefunctions.
The spin-spin interaction breaks the model SU(4) symmetry, providing a natural
mechanism for the difference between the up and down distributions. For a value
of sufficient to produce the mass splitting, we find up
and down quark distributions in reasonable agreement with experiment.Comment: 25 Pages, LA-UR-93-132
On the Flavor Structure of the Constituent Quark
We discuss the dressing of constituent quarks with a pseudoscalar meson cloud
within the effective chiral quark model. SU(3) flavor symmetry breaking effects
are included explicitly. Our results are compared with those of the traditional
meson cloud approach in which pions are coupled to the nucleon. The pionic
dressing of the constituent quarks explains the experimentally observed
violation of the Gottfried Sum Rule and leads to an enhanced nonperturbative
sea of quark-antiquark pairs in the constituent quark and consequently in the
nucleon. We find 2.5 times more pions and 10-15 times more kaons in the nucleon
than in the traditional picture.Comment: 7 pages, LaTeX, 4 Postscript figures, to appear in J. Phys.
The Casimir Effect in Spheroidal Geometries
We study the zero point energy of massless scalar and vector fields subject
to spheroidal boundary conditions. For massless scalar fields and small
ellipticity the zero-point energy can be found using both zeta function and
Green's function methods. The result agrees with the conjecture that the zero
point energy for a boundary remains constant under small deformations of the
boundary that preserve volume (the boundary deformation conjecture), formulated
in the case of an elliptic-cylindrical boundary. In the case of massless vector
fields, an exact solution is not possible. We show that a zonal approximation
disagrees with the result of the boundary deformation conjecture. Applying our
results to the MIT bag model, we find that the zero point energy of the bag
should stabilize the bag against deformations from a spherical shape.Comment: 24 pages, 3 figures. To appear in Phys. Rev.
Non-perturbative structure of the polarized nucleon sea
We investigate the flavour and quark-antiquark structure of the polarized
nucleon by calculating the parton distribution functions of the nucleon sea
using the meson cloud model. We find that the SU(2) flavor symmetry in the
light antiquark sea and quark-antiquark symmetry in the strange quark sea are
broken, {\it i.e.} \Delta\ubar < \Delta \dbar and \Delta s < \Delta \sbar.
The polarization of the strange sea is found to be positive, which is in
contradiction to previous analyses. We predict a much larger quark-antiquark
asymmetry in the polarized strange quark sea than that in the unpolarized
strange quark sea. Our results for both polarized light quark sea and polarized
strange quark sea are consistent with the recent HERMES data.Comment: RevTex, 17 pages plus 8 PS figure
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
Charge symmetry violation in the parton distributions of the nucleon
We point out that charge symmetry violation in both the valence and sea quark
distributions of the nucleon has a non-perturbative source. We calculate this
non-perturbative charge symmetry violation using the meson cloud model, which
has earlier been successfully applied to both the study of SU(2) flavour
asymmetry in the nucleon sea and quark-antiquark asymmetry in the nucleon. We
find that the charge symmetry violation in the valence quark distribution is
well below 1%, which is consistent with most low energy tests but significantly
smaller than the quark model prediction about 5%-10%. Our prediction for the
charge symmetry violation in the sea quark distribution is also much smaller
than the quark model calculation.Comment: RevTex, 26 pages, 6 PostScript figure
Nucleon Structure Functions at Moderate Q**2: Relativistic Constituent Quarks and Spectator Mass Spectrum
We present a model description of the nucleon valence structure function
applicable over the entire region of the Bjorken variable x, and above moderate
values of Q**2 (> 1 GeV**2). We stress the importance of describing the
complete spectrum of intermediate states which are spectator to the
deep-inelastic collision. At a scale of 1 GeV**2 the relevant degrees of
freedom are constituent quarks and pions. The large-x region is then described
in terms of scattering from constituent quarks in the nucleon, while the
dressing of constituent quarks by pions plays an important role at intermediate
x values. The correct small-x behavior, which is necessary for the proper
normalization of the valence distributions, is guaranteed by modeling the
asymptotic spectator mass spectrum according to Regge phenomenology.Comment: 44 pages RevTeX, 9 uuencoded figures, accepted for publication in
Nucl. Phys.
Parton Distributions for the Octet and Decuplet Baryons
We calculate the parton distributions for both polarized and unpolarized
octet and decuplet baryons, using the MIT bag, dressed by mesons. We show that
the hyperfine interaction responsible for the and splittings leads to large deviations from SU(3) and SU(6) predictions.
For the we find significant polarized, non-strange parton
distributions which lead to a sizable polarization in polarized,
semi-inclusive scattering. We also discuss the flavour symmetry violation
arising from the meson-cloud associated with the chiral structure of baryons.Comment: 29 pages, 15 figure
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