1,345 research outputs found
The Strangeness Radius and Magnetic Moment of the Nucleon Revisited
We update Jaffe's estimate of the strange isoscalar radius and magnetic
moment of the nucleon. We make use of a recent dispersion--theoretical fit to
the nucleon electromagnetic form factors and an improved description of
symmetry breaking in the vector nonet. We find ~n.m.
and ~fm. The strange formfactor follows
a dipole with a cut--off mass of 1.46~GeV, . These numbers should be considered as upper limits on the
strange vector current matrix--elements in the nucleon.Comment: 8 pp, LaTeX, uses epsf, 1 figure in separate fil
A complex of seven vaccinia virus proteins conserved in all chordopoxviruses is required for the association of membranes and viroplasm to form immature virions
AbstractEarly events in vaccinia virus (VAC) morphogenesis, particularly the formation of viral membranes and their association with viroplasm, are poorly understood. Recently, we showed that repression of A30 or G7 expression results in the accumulation of normal viral membranes that form empty-looking immature virions (IV), which are separated from large masses of electron-dense viroplasm. In addition, A30 and G7 physically and functionally interact with each other and with the F10 protein kinase. To identify other proteins involved in early morphogenesis, proteins from cells that had been infected with vaccinia virus expressing an epitope-tagged copy of F10 were purified by immunoaffinity chromatography and analyzed by gel electrophoresis. In addition to F10, A30, and G7, viral proteins A15, D2, D3, and J1 were identified by mass spectrometry of tryptic peptides. Further evidence for the complex was obtained by immunopurification of proteins associated with epitope-tagged A15, D2, and D3. The previously unstudied A15, like other proteins in the complex, was expressed late in infection, associated with virus cores, and required for the stability and kinase activity of F10. Biochemical and electron microscopic analyses indicated that mutants in which A15 or D2 expression was regulated by the Escherichia coli lac operator system exhibited phenotypes characterized by the presence of large numbers of empty immature virions, similar to the results obtained with inducible A30 and G7 mutants. Empty immature virions were also seen by electron microscopy of cells infected with temperature-sensitive mutants of D2 or D3, though the numbers of membrane forms were reduced perhaps due to additional effects of high temperature
Momentum Dependent Vertices , and : The NJL Scalar Hidden by Chiral Symmetry
We calculate the momentum dependence of three particle vertices , and in the context of a
Nambu Jona Lasinio type model. We show how they influence the processes , and and how chiral symmetry
shadows the presence of the .Comment: 9 pages (latex), 5 figures available from the authors, preprint
Coimbra 940506, IJS-TP-94/10, accepted for publication in Zeit. f. Physik
Pion Structure Function in the Nambu and Jona-Lasinio model
The pion structure function is studied in the Nambu and Jona-Lasinio (NJL)
model. We calculate the forward scattering amplitude of a virtual photon from a
pion target in the Bjorken limit, and obtain valence quark distributions of the
pion at the low energy hadronic scale, where the NJL model is supposed to work.
The calculated distribution functions are evolved to the experimental momentum
scale using the Altarelli-Parisi equation. The resulting distributions are in a
reasonable agreement with experiment. We calculate also the kaon structure
function and compare the ratio of kaon to pion valence u-quark distributions
with experiment.Comment: 15 pages with 5 figures as uuencoded postscript files, TMU-NT-930301
(plain LaTeX
Delocalization of the axial charge in the chiral limit
The nucleon's axial vector charge, g_A, becomes delocalized in the chiral
limit. When m_\pi = 0, and SU(2)_L x SU(2)_R is exact, 1/3 of the nucleon's
axial charge is to be found at infinite distance from the nucleon. For finite
m_\pi this result is approached smoothly as m_\pi -> 0. We illustrate this
effect by considering the lepton-proton spin-spin interaction arising from Z^0
exchange as a function of m_\pi. Delocalization may have implications for
lattice calculations of g_A and in nuclei.Comment: Revised content: Further explanation of the limit m_pi -> 0 and an
example of a physical process (spin-spin interaction in a hydrogenic atom
mediated by Z^0 exchange) which can, in principle, measure the delocalization
of g_A. Ten pages using RevTeX; email correspondence to R.L. Jaffe
<[email protected]
Critical Analysis of Baryon Masses and Sigma-Terms in Heavy Baryon Chiral Perturbation Theory
We present an analysis of the octet baryon masses and the and
--terms in the framework of heavy baryon chiral perturbation theory. At
next-to-leading order, , knowledge of the baryon masses and
allows to determine the three corresponding finite
low--energy constants and to predict the the two --terms
. We also include the spin-3/2 decuplet in the
effective theory. The presence of the non--vanishing energy scale due to the
octet--decuplet splitting shifts the average octet baryon mass by an infinite
amount and leads to infinite renormalizations of the low--energy constants. The
first observable effect of the decuplet intermediate states to the baryon
masses starts out at order . We argue that it is not sufficient to retain
only these but no other higher order terms to achieve a consistent description
of the three--flavor scalar sector of baryon CHPT. In addition, we critically
discuss an SU(2) result which allows to explain the large shift of via intermediate states.Comment: 18 pp, TeX, BUTP-93/05 and CRN-93-0
Nucleon Structure Functions from Relativistic Constituent Quarks
We investigate deep inelastic lepton scattering from the nucleon within a
constituent quark picture, in which the internal structure of constituent
quarks is modeled by meson and diquark dressing. In a covariant framework this
structure leads to a breakdown of the factorization necessary for a convolution
formulation. We perform our analysis in time-ordered perturbation theory in the
infinite momentum frame where factorization of subprocesses is automatic.
Numerical results are compared with recent data on valence quark distributions
in the proton.Comment: 10 pages LaTeX, 3 figures available upon request, TPR-94-7, to appear
in Physics Letters
Baryon form factors: Model-independent results
Baryon form factors can be analyzed in a largely model-independent fashion in
terms of two complementary approaches. These are chiral perturbation theory and
dispersion relations. I review the status of dispersive calculations of the
nucleon electromagnetic form factors in the light of new data. Then, I present
the leading one-loop chiral perturbation theory analysis of the hyperon and the
strange nucleon form factors. Open problems and challenges are also discussed.Comment: 10 pp, LaTeX, 10 figures, plenary talk, NUCLEON '99, Frascati, June
1999, to appear in the proceedings (Nucl. Phys. A), typos corrected,
references update
Strange chiral nucleon form factors
We investigate the strange electric and magnetic form factors of the nucleon
in the framework of heavy baryon chiral perturbation theory to third order in
the chiral expansion. All counterterms can be fixed from data. In particular,
the two unknown singlet couplings can be deduced from the parity-violating
electron scattering experiments performed by the SAMPLE and the HAPPEX
collaborations. Within the given uncertainties, our analysis leads to a small
and positive electric strangeness radius, .
We also deduce the consequences for the upcoming MAMI A4 experiment.Comment: 7 pp, REVTeX, uses epsf, minor correction
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