138,204 research outputs found
The Validity of Charge Symmetry for Parton Distributions
Recent measurements of the Gottfried sum rule have focused attention on the
possibility of substantial flavor symmetry breaking in the proton sea. This is
confirmed by pp and pD Drell-Yan processes measured at FNAL. Theoretical models
used to `prove' flavor symmetry breaking rely on the assumption of charge
symmetric parton distributions. Substantial charge symmetry violation [CSV]
could affect current tests of flavor symmetry. In this review we examine the
possibility of CSV for parton distributions. We first give definitions for
structure functions without making the usual assumption of charge symmetry.
Next we make estimates of CSV for both valence and sea quark distributions. We
list a set of relations which must hold if charge symmetry is valid, and review
current experimental limits on CSV. We propose a series of experimental tests
of charge symmetry. These tests could either detect CSV, or they could provide
stronger upper limits on CSV effects. We discuss CSV contributions to sum
rules, and we propose sum rules which could differentiate between flavor
symmetry, and charge symmetry violation in nuclear systems.Comment: 74 pages, including 26 figure
Cross-sensitization between poppy seed and buckwheat in a food-allergic patient with poppy seed anaphylaxis
The opium poppy, Papaver somniferum L., is the source of both poppy seeds and opium. The commercially available seeds are widely used as ingredients for various kinds of food. IgE-mediated sensitization to poppy seeds is rare, but, if present, clinical symptoms are usually severe. Cross-sensitizations between poppy seeds and other food allergens have been described with sesame, hazelnut, rye grain and kiwi fruit. We report the case of a 17-year-old female with an apparently food-allergic reaction after ingestion of a poppy seed cake. Allergological workup revealed a poppy seed anaphylaxis and led to the identification of a novel cross-sensitization with buckwheat. Copyright (c) 2006 S. Karger AG, Basel
Additional Corrections to the Gross-Llewellyn Smith Sum Rule
We investigate some QCD corrections that contribute to the Gross-Llewellyn
Smith (GLS) sum rule, but have not been included in previous analyses of it. We
first review the techniques by which the xF3 structure function is extracted
from combinations of neutrino and antineutrino cross sections. Next we
investigate corrections to the GLS sum rule, with particular attention to
contributions arising from strange quark contributions and from charge symmetry
violating (CSV) parton distributions. We find that additional corrections from
strange quarks and parton CSV are likely to have a small but potentially
significant role in decreasing the current discrepancy between the experimental
and theoretical estimates of the Gross-Llewellyn Smith sum rule.Comment: 13 pages, 6 figure
Differences between stellar and laboratory reaction cross sections
Nuclear reactions proceed differently in stellar plasmas than in the
laboratory due to the thermal effects in the plasma. On one hand, a target
nucleus is bombarded by projectiles distributed in energy with a distribution
defined by the plasma temperature. The most relevant energies are low by
nuclear physics standards and thus require an improved description of
low-energy properties, such as optical potentials, required for the calculation
of reaction cross sections. Recent studies of low-energy cross sections suggest
the necessity of a modification of the proton optical potential. On the other
hand, target nuclei are in thermal equilibrium with the plasma and this
modifies their reaction cross sections. It is generally expected that this
modification is larger for endothermic reactions. We show that there are many
exceptions to this rule.Comment: 4 pages, Proceedings of Nuclear Physics in Astrophysics 4, Frascati,
Italy; to appear in J. Phys. Conf. Serie
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