887 research outputs found
Representations in Density Dependent Hadronic Field Theory and compatibility with QCD sum-rules
Different representations of an effective, covariant theory of the hadronic
interaction are examined. For this purpose we have introduced nucleon-meson
vertices parametrized in terms of scalar combinations of hadronic fields,
extending the conceptual frame of the Density Dependent Hadronic Field Theory.
Nuclear matter properties at zero temperature are examined in the Mean Field
Approximation, including the equation of state, the Landau parameters, and
collective modes. The treatment of isospin channels in terms of QCD sum rules
inputs is outlined.Comment: 23 pages, 6 PostScript figures, Revtex4 clas
Relativistic models of the neutron-star matter equation of state
Motivated by a recent astrophysical measurement of the pressure of cold
matter above nuclear-matter saturation density, we compute the equation of
state of neutron star matter using accurately calibrated relativistic models.
The uniform stellar core is assumed to consist of nucleons and leptons in beta
equilibrium; no exotic degrees of freedom are included. We found the
predictions of these models to be in fairly good agreement with the measured
equation of state. Yet the Mass-vs-Radius relations predicted by these same
models display radii that are consistently larger than the observations.Comment: Submitted to Physical Review C (5 pages with 2 figures and 2 tables
Impact of spin-orbit currents on the electroweak skin of neutron-rich nuclei
Background: Measurements of neutron radii provide important constraints on
the isovector sector of nuclear density functionals and offer vital guidance in
areas as diverse as atomic parity violation, heavy-ion collisions, and
neutron-star structure. Purpose: To assess the impact of spin-orbit currents on
the electromagnetic- and weak-charge radii of a variety of nuclei. Special
emphasis is placed on the experimentally accessible electroweak skin, defined
as the difference between weak-charge and electromagnetic-charge radii.
Methods: Two accurately calibrated relativistic mean field models are used to
compute proton, neutron, charge, and weak-charge radii of a variety of nuclei.
Results: We find that spin-orbit contributions to the electroweak skin of light
neutron-rich nuclei, such as 22O and 48Ca, are significant and result in a
substantial increase in the size of the electroweak skin relative to the
neutron skin. Conclusions: Given that spin-orbit contributions to both the
charge and weak-charge radii of nuclei are often as large as present or
anticipated experimental error bars, future calculations must incorporate
spin-orbit currents in the calculation of electroweak form factors.Comment: 17 pages, 2 figures, and 2 table
Dirac Sea Contribution in Relativistic Random Phase Approximation
In the hadrodynamics (QHD) there are two methods to take account of the
contribution of negative-energy states in the relativistic random phase
approximation (RRPA). Dawson and Furnstahl made the ansatz that the Dirac sea
were empty, while according to the Dirac hole theory the sea should be fully
occupied. The two methods seem contradictory. Their close relationship and
compatibility are explored and in particular the question of the ground-state
(GS) instability resulting from Dawson-Furnstanhl's ansatz is discussed.Comment: 17 pages, 4 figures (the revised version.The paper and figures are
revised). accepted by J. Phys.
Integrating out the Dirac sea in the Walecka model
We derive a purely fermionic no-sea effective theory, featuring
positive-energy states only for the Walecka model. In contrast to the so-called
mean-field theory approach with the no-sea approximation, where the Dirac sea
is simply omitted from the outset, we turn to the relativistic Hartree
approximation and explicitly construct a no-sea effective theory from the
underlying quantum field theory. Several results obtained within these two
approaches are confronted with each other. This sheds new light on the
reliability of the mean-field theory with the no-sea approximation as well as
the role of the Dirac sea. Restricting to 1+1 dimensions, we obtain new
analytical insights into nonuniform nuclear matter.Comment: 15 pages, 8 figures, several points clarified, Fig.7 replaced,
references adde
Superfluidity of hyperons in neutron stars
We study the superfluidity of hyperons in neutron star
matter and neutron stars. We use the relativistic mean field (RMF) theory to
calculate the properties of neutron star matter. In the RMF approach, the
meson-hyperon couplings are constrained by reasonable hyperon potentials that
include the updated information from recent developments in hypernuclear
physics. To examine the pairing gap of hyperons, we employ
several interactions based on the Nijmegen models and used in
double- hypernuclei studies. It is found that the maximal pairing gap
obtained is a few tenths of a MeV. The magnitude and the density region of the
pairing gap are dependent on the interaction and the treatment
of neutron star matter. We calculate neutron star properties and find that
whether the superfluidity of hyperons exists in the core of
neutron stars mainly depends on the interaction used.Comment: 22 pages, 2 Tables, 6 Figur
Melting of antikaon condensate in protoneutron stars
We study the melting of a condensate in hot and neutrino-trapped
protoneutron stars. In this connection, we adopt relativistic field theoretical
models to describe the hadronic and condensed phases. It is observed that the
critical temperature of antikaon condensation is enhanced as baryon density
increases. For a fixed baryon density, the critical temperature of antikaon
condensation in a protoneutron star is smaller than that of a neutron star. We
also exhibit the phase diagram of a protoneutron star with a condensate.Comment: 17 pages including 7 figure
Neutral-current neutrino-nucleus cross sections based on relativistic nuclear energy density functional
Background: Inelastic neutrino-nucleus scattering through the weak
neutral-current plays important role in stellar environment where transport of
neutrinos determine the rate of cooling. Since there are no direct experimental
data on neutral-current neutrino-nucleus cross sections available, only the
modeling of these reactions provides the relevant input for supernova
simulations. Purpose: To establish fully self-consistent framework for
neutral-current neutrino-nucleus reactions based on relativistic nuclear energy
density functional. Methods: Neutrino-nucleus cross sections are calculated
using weak Hamiltonian and nuclear properties of initial and excited states are
obtained with relativistic Hartree-Bogoliubov model and relativistic
quasiparticle random phase approximation that is extended to include pion
contributions for unnatural parity transitions. Results: Inelastic
neutral-current neutrino-nucleus cross sections for 12C, 16O, 56Fe, 56Ni, and
even isotopes {92-100}Mo as well as respective cross sections averaged over
distribution of supernova neutrinos. Conclusions: The present study provides
insight into neutrino-nucleus scattering cross sections in the neutral channel,
their theoretical uncertainty in view of recently developed microscopic models,
and paves the way for systematic self-consistent large-scale calculations
involving open-shell target nuclei.Comment: 25 pages, 9 figures, 2 tables, submitted to Physical Review
Inclusive Photoproduction of Mesons on Nuclei and the in-medium properties of the S Resonance
A relativistic non-local model for the inclusive photoproduction of
mesons from complex nuclei is introduced. The model is based on the dominance
of the S(1535) resonance. We compare the results of our calculations
with the available data on inclusive cross sections for the nuclei C, Al and
Cu. Assuming the resonance propagates freely in the nuclear medium, we find
that the calculated angular distribution and energy dependence of the cross
sections reproduce the data in a reasonable fashion. The present non-local
model allows the inclusion of density dependent mass and width in the
calculations. Including these in the calculations reveals that the presently
available data do not show clear preference for the inclusion of such
modifications of the properties of the S(1535) in the nuclear medium.Comment: 15 pages, 8 figure
Integrating out the Dirac sea: Effective field theory approach to exactly solvable four-fermion models
We use 1+1 dimensional large N Gross-Neveu models as a laboratory to derive
microscopically effective Lagrangians for positive energy fermions only. When
applied to baryons, the Euler-Lagrange equation for these effective theories
assumes the form of a non-linear Dirac equation. Its solution reproduces the
full semi-classical results including the Dirac sea to any desired accuracy.
Dynamical effects from the Dirac sea are encoded in higher order derivative
terms and multi-fermion interactions with perturbatively calculable, finite
coefficients. Characteristic differences between models with discrete and
continuous chiral symmetry are observed and clarified.Comment: 13 pages, 11 figures; v2: typos corrected (Eqs. 4 and 44
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