1,985 research outputs found
On the pentaquark candidates p+c (4380) and p+c (4450) within the soliton picture of baryons
Using the bound state version of the topological soliton model for the baryons we show that the existence of a bound (or quasi-bound) D-soliton state leads to the possibility of having hidden charm pentaquarks with quantum numbers and masses, which are compatible with those of the candidates recently reported by the LHCb experiment. The implications of heavy quark symmetry are elaborated.Fil: Scoccola, Norberto Nerio. Universidad Favaloro. Facultad de Ingeniería y Ciencias Exactas y Naturales; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones no Nucleares. Gerencia Física (CAC). Grupo de Física Teórica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Riska, D. O.. Finnish Society Of Science And Letters; FinlandiaFil: Rho, María Gabriela. Centre D'etudes de Saclay; Franci
The Solar pp and hep Processes in Effective Field Theory
The strategy of modern effective field theory is exploited to pin down
accurately the flux factors for the and processes in the Sun.
The technique used is to combine the high accuracy established in few-nucleon
systems of the "standard nuclear physics approach" (SNPA) and the systematic
power counting of chiral perturbation theory (ChPT) into a consistent effective
field theory framework. Using highly accurate wave functions obtained in the
SNPA and working to \nlo3 in the chiral counting for the current, we make
totally parameter-free and error-controlled predictions for the and
processes in the Sun.Comment: 5 pages, aipproc macros are included. Talk given at International
Nuclear Physics Conference 2001, Berkeley, California, July 30 - August 3,
200
Neutrino Interactions In Color-Flavor-Locked Dense Matter
At high density, diquarks could condense in the vacuum with the QCD color
spontaneously broken. Based on the observation that the symmetry breaking
pattern involved in this phenomenon is essentially the same as that of the
Pati-Salam model with broken electroweak--color SU(3) group, we determine the
relevant electroweak interactions in the color-flavor locked (CFL) phase in
high density QCD. We briefly comment on the possible implications on the
cooling of neutron stars.Comment: 13 pages. LaTeX. Talk given at the First KIAS Workshop on
Astrophysics, Seoul, May 2000; V2. references added. comments on cooling
change
The Gluon Spin in the Chiral Bag Model
We study the gluon polarization contribution at the quark model
renormalization scale to the proton spin, , in the chiral bag model. It
is evaluated by taking the expectation value of the forward matrix element of a
local gluon operator in the axial gauge . It is shown that the confining
boundary condition for the color electric field plays an important role. When a
solution satisfying the boundary condition for the color electric field, which
is not the conventionally used but which we favor, is used, the has a
positive value for {\it all} bag radii and its magnitude is comparable to the
quark spin polarization. This results in a significant reduction in the
relative fraction of the proton spin carried by the quark spin, which is
consistent with the small flavor singlet axial current measured in the EMC
experiments.Comment: Corrections to figure
Nucleon Form Factors and Hidden Symmetry in Holographic QCD
The vector dominance of the electromagnetic form factors both for mesons and
baryons arises naturally in holographic QCD, where both the number of colors
and the 't Hooft coupling are taken to be very large, offering a bona-fide
derivation of the notion of vector dominance. The crucial ingredient for this
is the infinite tower of vector mesons in the approximations made which share
features that are characteristic of the quenched approximation in lattice QCD.
We approximate the infinite sum by contributions from the lowest four vector
mesons of the tower which turn out to saturate the charge and magnetic moment
sum rules within a few percent and compute them totally free of unknown
parameters for momentum transfers Q^2 less than 1GeV^2. We identify certain
observables that can be reliably computed within the approximations and others
that are not, and discuss how the improvement of the latter can enable one to
bring holographic QCD closer to QCD proper.Comment: 18 pages, 4 figures, revtex4; one reference added, final version to
appear in Phys. Rev.
Numerical Simulations of Supernova Dust Destruction. II. Metal-Enriched Ejecta Knots
Following our previous work, we investigate through hydrodynamic simulations
the destruction of newly-formed dust grains by sputtering in the reverse shocks
of supernova remnants. Using an idealized setup of a planar shock impacting a
dense, spherical clump, we implant a population of Lagrangian particles into
the clump to represent a distribution of dust grains in size and composition.
We vary the relative velocity between the reverse shock and ejecta clump to
explore the effects of shock-heating and cloud compression. Because supernova
ejecta will be metal-enriched, we consider gas metallicities from Z/Zsun = 1 to
100 and their influence on cooling properties of the cloud and the thermal
sputtering rates of embedded dust grains. We post-process the simulation output
to calculate grain sputtering for a variety of species and size distributions.
In the metallicity regime considered in this paper, the balance between
increased radiative cooling and increased grain erosion depends on the impact
velocity of the reverse shock. For slow shocks (velocity less than or equal to
3000 km/s), the amount of dust destruction is comparable across metallicities,
or in some cases is decreased with increased metallicity. For higher shock
velocities (velocity greater than or equal to 5000 km/s), an increase in
metallicity from Z/Zsun = 10 to 100 can lead to an additional 24% destruction
of the initial dust mass. While the total dust destruction varies widely across
grain species and simulation parameters, our most extreme cases result in
complete destruction for some grain species and only 44% dust mass survival for
the most robust species. These survival rates are important in understanding
how early supernovae contribute to the observed dust masses in high-redshift
galaxies.Comment: 10 pages, 6 figures, 2 tables, changes made to the text and figures
as suggested by the anonymous referee, accepted by the Astrophysical Journa
Half-Skyrmions, Tensor Forces and Symmetry Energy in Cold Dense Matter
In a previous article, the 4D half-skyrmion (or 5D dyonic salt) structure of
dense baryonic matter described in crystalline configuration in the large
limit was shown to impact nontrivially on how anti-kaons behave in compressed
nuclear matter with a possible implication on an "ice-9" phenomenon of deeply
bound kaonic matter and condensed kaons in compact stars. We extend the
analysis to make a further prediction on the scaling properties of hadrons that
have a surprising effect on the nuclear tensor forces, the symmetry energy and
hence on the phase structure at high density. We treat this problem relying on
certain topological structure of chiral solitons. Combined with what can be
deduced from hidden local symmetry for hadrons in dense medium and the "soft"
dilatonic degree of freedom associated with the trace anomaly of QCD, we
uncover a novel structure of chiral symmetry in the "supersoft" symmetry energy
that can influence the structure of neutron stars.Comment: 8 pages, 4 figures; contents unchanged but expanded for a journa
Persuasion, influence, and participatory modelling in socio-ecological systems: A framework for action
The Three-Dimensional Structure of Interior Ejecta in Cassiopeia A at High Spectral Resolution
We used the Spitzer Space Telescope's Infrared Spectrograph to create a high
resolution spectral map of the central region of the Cassiopeia A supernova
remnant, allowing us to make a Doppler reconstruction of its 3D structure. The
ejecta responsible for this emission have not yet encountered the remnant's
reverse shock or the circumstellar medium, making it an ideal laboratory for
exploring the dynamics of the supernova explosion itself. We observe that the
O, Si, and S ejecta can form both sheet-like structures as well as filaments.
Si and O, which come from different nucleosynthetic layers of the star, are
observed to be coincident in velocity space in some regions, and separated by
500 km/s or more in others. Ejecta traveling toward us are, on average, ~900
km/s slower than the material traveling away from us. We compare our
observations to recent supernova explosion models and find that no single model
can simultaneously reproduce all the observed features. However, models of
different supernova explosions can collectively produce the observed geometries
and structures of the interior emission. We use the results from the models to
address the conditions during the supernova explosion, concentrating on
asymmetries in the shock structure. We also predict that the back surface of
Cassiopeia A will begin brightening in ~30 years, and the front surface in ~100
years.Comment: 35 pages, 16 figures, accepted to Ap
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