1,855 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
Analysis of dynamical corrections to baryon magnetic moments
We present and analyze QCD corrections to the baryon magnetic moments in
terms of the one-, two-, and three-body operators which appear in the effective
field theory developed in our recent papers. The main corrections are extended
Thomas-type corrections associated with the confining interactions in the
baryon. We investigate the contributions of low-lying angular excitations to
the moments quantitatively and show that they are completely negligible. When
the QCD corrections are combined with the non-quark model contributions of the
meson loops, we obtain a model which describes the moments within a mean
deviation of 0.04 . The nontrivial interplay of the two types of
corrections to the quark-model moments is analyzed in detail, and explains why
the quark model is so successful. In the course of these calculations, we
parametrize the general spin structure of the baryon wave functions
in a form which clearly displays the symmetry properties and the internal
angular momentum content of the wave functions, and allows us to use spin-trace
methods to calculate the many spin matrix elements which appear in the
expressions for the moments. This representation may be useful elsewhere.Comment: 32 pages, 3 figures, submitted to Phys. Rev.
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
Perceptions of Violence against Women among College Students in the United States, Japan, India, Vietnam and China
Violence against women is a global health issue that threatens the health and human rights of women. Intimate partner violence (IPV) and sexual violence are the most common forms of violence against women. While previous studies examined incidence of IPV and other forms of violence against women in the United States (US), little is known about variations in the perceptions of violence against women among college students in other countries. This study explored differences in perceptions of violence against women among college students in the US, Japan, India, Vietnam and China. A total of 1,136 college students from these countries participated in a self-administered survey in 2012-2013. The students’ perceptions about the prevalence of domestic violence is in their country varied across countries. Furthermore, more than half of the students across the countries perceived alcoholism and drug addiction to be causes of domestic violence against women. It was also found that the levels of knowledge about laws on domestic violence in their country varied among the students. These findings show the importance of understanding country level variations that may affect violence against women. The results of this study provide important insights by documenting cross country variations in students’ perceptions about violence against women that can provide helpful inputs in framing country-specific programs and policies to prevent violence against women. Keywords: Violence against women, perceptions, college students, the United States, Japan, India, Vietnam, Chin
Aerothermodynamic Analysis of a Reentry Brazilian Satellite
This work deals with a computational investigation on the small ballistic
reentry Brazilian vehicle SARA (acronyms for SAt\'elite de Reentrada
Atmosf\'erica). Hypersonic flows over the vehicle SARA at zero-degree angle of
attack in a chemical equilibrium and thermal non-equilibrium are modeled by the
Direct Simulation Monte Carlo (DSMC) method, which has become the main
technique for studying complex multidimensional rarefied flows, and that
properly accounts for the non-equilibrium aspects of the flows. The emphasis of
this paper is to examine the behavior of the primary properties during the high
altitude portion of SARA reentry. In this way, velocity, density, pressure and
temperature field are investigated for altitudes of 100, 95, 90, 85 and 80 km.
In addition, comparisons based on geometry are made between axisymmetric and
planar two-dimensional configurations. Some significant differences between
these configurations were noted on the flowfield structure in the reentry
trajectory. The analysis showed that the flow disturbances have different
influence on velocity, density, pressure and temperature along the stagnation
streamline ahead of the capsule nose. It was found that the stagnation region
is a thermally stressed zone. It was also found that the stagnation region is a
zone of strong compression, high wall pressure. Wall pressure distributions are
compared with those of available experimental data and good agreement is found
along the spherical nose for the altitude range investigated.Comment: The paper will be published in Vol. 42 of the Brazilian Journal of
Physic
Baryon Magnetic Moments in a QCD-based Quark Model with loop corrections
We study meson loop corrections to the baryon magnetic moments starting from
a QCD-based quark model derived earlier in a quenched approximation to QCD. The
model reproduces the standard quark model with extra corrections for the
binding of the quarks. The loop corrections are necessary to remove the
quenching. Our calculations use heavy baryon perturbation theory with chiral
baryon-meson couplings and a form factor characterizing the structure of
baryons as composite particles. The form factor reflects soft wave function
effects with characteristic momenta MeV, well below the usual
chiral cutoff of GeV. The resulting model involves only three
parameters, the quark moments and and a parameter
that sets the momentum scale in the wavefunctions. We find that this approach
substantially improves the agreement between the theoretical and experimental
values of the octet baryon magnetic moments, with an average difference between
the theoretical and experimental moments of 0.05. An extension to the
decuplet states using the same input predicts a moment of 1.97 for the
hyperon, in excellent agreement with the measured moment of
.Comment: 23 pages, 3 figure
The Underestimation Of Egocentric Distance: Evidence From Frontal Matching Tasks
There is controversy over the existence, nature, and cause of error in egocentric distance judgments. One proposal is that the systematic biases often found in explicit judgments of egocentric distance along the ground may be related to recently observed biases in the perceived declination of gaze (Durgin & Li, Attention, Perception, & Psychophysics, in press), To measure perceived egocentric distance nonverbally, observers in a field were asked to position themselves so that their distance from one of two experimenters was equal to the frontal distance between the experimenters. Observers placed themselves too far away, consistent with egocentric distance underestimation. A similar experiment was conducted with vertical frontal extents. Both experiments were replicated in panoramic virtual reality. Perceived egocentric distance was quantitatively consistent with angular bias in perceived gaze declination (1.5 gain). Finally, an exocentric distance-matching task was contrasted with a variant of the egocentric matching task. The egocentric matching data approximate a constant compression of perceived egocentric distance with a power function exponent of nearly 1; exocentric matches had an exponent of about 0.67. The divergent pattern between egocentric and exocentric matches suggests that they depend on different visual cues
- …