255 research outputs found
Effective field theory and the quark model
We analyze the connections between the quark model (QM) and the description
of hadrons in the low-momentum limit of heavy-baryon effective field theory in
QCD. By using a three-flavor-index representation for the effective baryon
fields, we show that the ``nonrelativistic'' constituent QM for baryon masses
and moments is completely equivalent through O(m_s) to a parametrization of the
relativistic field theory in a general spin--flavor basis. The flavor and spin
variables can be identified with those of effective valence quarks. Conversely,
the spin-flavor description clarifies the structure and dynamical
interpretation of the chiral expansion in effective field theory, and provides
a direct connection between the field theory and the semirelativistic models
for hadrons used in successful dynamical calculations. This allows dynamical
information to be incorporated directly into the chiral expansion. We find, for
example, that the striking success of the additive QM for baryon magnetic
moments is a consequence of the relative smallness of the non-additive
spin-dependent corrections.Comment: 25 pages, revtex, no figure
Asymptotic behaviour of the total cross section of p-p scattering and the Akeno cosmic ray data
I present a new determination of the total cross section for proton-proton
collisions from the recent Akeno results on absorption of the cosmic ray
protons in the p-Air collisions. Extrapolation to the SSC energy suggests
. I also comment on a possible
sensitivity of the p-Air cross section determinations to assumptions on the
inelasticity of nuclear collisions at high energy.Comment: . 6 pages, 0 figure
Evidence for Host Genome Involvement in Cytokinin Metabolism by Male and Female Cells of Mercurialis annua
Baryon Octet magnetic moments in PT: More on the importance of the Decuplet
We address the impact of treating the decuplet of spin-3/2 baryons as an
explicit degree of freedom in the chiral expansion of the magnetic moments of
the octet of spin-1/2 baryons. We carry out a complete calculation of the octet
moments to O(1/\lamchic), including decuplet contributions to the chiral loops.
In contrast to results of previous analyses, we find that inclusion of the
decuplet preserves the convergence behavior of the chiral expansion implied by
power counting arguments.Comment: 17 pages, 2 figures. Includes axodraw.sty needed for figures Minor
typos correcte
Diffractive Dissociation and Eikonalization in High Energy pp and p Collisions
We show that eikonal corrections imposed on diffraction dissociation
processes calculated in the triple Regge limit, produce a radical change in the
energy dependence of the predicted cross section. The induced correction is
shown to be in general agreement with the new experimental data measured at the
Tevatron.Comment: 11 pages LATEX, ( two figures not included obtainable from authors)
(TAUP 2066-93 and FERMILAB PUB 93/ T
Hyperon Nonleptonic Decays in Chiral Perturbation Theory Reexamined
We recalculate the leading nonanalytic contributions to the amplitudes for
hyperon nonleptonic decays in chiral perturbation theory. Our results partially
disagree with those calculated before, and include new terms previously omitted
in the P-wave amplitudes. Although these modifications are numerically
significant, they do not change the well-known fact that good agreement with
experiment cannot be simultaneously achieved using one-loop S- and P-wave
amplitudes.Comment: 14 pages, latex, 3 figures, uses axodraw.sty, minor additions, to
appear in Phys. Rev.
Thermally activated composite with two-way and multi-shape memory effects
The use of shape memory polymer composites is growing rapidly in smart structure applications. In this work, an active asymmetric composite called “controlled behavior composite material (CBCM)” is used as shape memory polymer composite. The programming and the corresponding initial fixity of the composite structure is obtained during a bending test, by heating CBCM above thermal glass transition temperature of the used Epoxy polymer. The shape memory properties of these composites are investigated by a bending test. Three types of recoveries are conducted, two classical recovery tests: unconstrained recovery and constrained recovery, and a new test of partial recovery under load. During recovery, high recovery displacement and force are produced that enables the composite to perform strong two-way actuations along with multi-shape memory effect. The recovery force confirms full recovery with two-way actuation even under a high load. This unique property of CBCM is characterized by the recovered mechanical wor
Baryon masses in a loop expansion with form factor
We show that the average multiplet masses in the baryon octet and decuplet
can be fitted with an average error of only MeV in a meson loop
expansion with chiral SU(6) couplings, with the hadrons treated as composite
particles using a baryon-meson form factor. The form factor suppresses
unphysical short distance effects and leads to a controllable expansion. We
find, in contrast to the results of standard chiral perturbation theory, that
pion loops are as important as kaon or eta loops as would be expected when only
intermediate- and long-distance contributions are retained. We also find that
the contributions of decuplet intermediate states are important in the
calculation of the masses, and those states must be included explicitly in a
consistent theory. These results agree with those of our recent loop-expansion
analysis of the baryon magnetic moments. We show, finally, that the parts of
the loop contributions that change the tree-level structure of the baryon
masses are small, but largely account for the violations of the baryon mass sum
rules which hold at tree level.Comment: 20 pages, 2 figures, submitted to Phys. Rev. D. Title changed, the
introduction and discussion of the results rewritte
Nucleon Magnetic Moments Beyond the Perturbative Chiral Regime
The quark mass dependence of nucleon magnetic moments is explored over a wide
range. Quark masses currently accessible to lattice QCD, which lie beyond the
regime of chiral perturbation theory (chiPT), are accessed via the cloudy bag
model (CBM). The latter reproduces the leading nonanalytic behavior of chiPT,
while modeling the internal structure of the hadron under investigation. We
find that the predictions of the CBM are succinctly described by the simple
formula, \mu_N(m_\pi) = \mu^{(0)}_N / (1 + \alpha m_\pi + \beta m_\pi^2), which
reproduces the lattice data, as well as the leading nonanalytic behavior of
chiPT. As this form also incorporates the anticipated Dirac moment behavior in
the limit m_\pi \to \infty, it constitutes a powerful method for extrapolating
lattice results to the physical mass regime.Comment: Revised version accepted for publication includes a new section
demonstrating extrapolations of lattice QCD result
A comparative study of some properties of cassava and tree cassava starch films
Cassava and tree cassava starch films plasticized with glycerol were produced by casting method. Different glycerol contents (30, 35, 40 and 45 wt. % on starch dry basis) were used and the resulting films were fully characterized. Their water barrier and mechanical properties were compared. While increasing glycerol concentration, moisture content, water solubility, water vapour permeability, tensile strength, percent elongation at break and Young's modulus decreased for both cassava and tree cassava films. Tree cassava films presented better values of water vapour permeability, water solubility and percent elongation at break compared to those of cassava films, regardless of the glycerol content
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