692 research outputs found
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.
Superscaling Predictions for Neutral Current Quasielastic Neutrino-Nucleus Scattering
The application of superscaling ideas to predict neutral-current (NC)
quasielastic (QE) neutrino cross sections is investigated. Results obtained
within the relativistic impulse approximation (RIA) using the same relativistic
mean field potential (RMF) for both initial and final nucleons -- a model that
reproduces the experimental (e,e') scaling function -- are used to illustrate
the ideas involved. While NC reactions are not so well suited for scaling
analyses, to a large extent the RIA-RMF predictions do exhibit superscaling.
Independence of the scaled response on the nuclear species is very well
fulfilled. The RIA-RMF NC superscaling function is in good agreement with the
experimental (e,e') one. The idea that electroweak processes can be described
with a universal scaling function, provided that mild restrictions on the
kinematics are assumed, is shown to be valid.Comment: 4 pages, 4 figures, published in PR
Quasielastic neutrino-nucleus scattering
We study the sensitivity of neutral-current neutrino-nucleus scattering to
the strange-quark content of the axial-vector form factor of the nucleon. A
model-independent formalism for this reaction is developed in terms of eight
nuclear structure functions. Taking advantage of the insensitivity of the ratio
of proton to neutron yields to distortion
effects, we compute all structure functions in a relativistic plane wave
impulse approximation approach. Further, by employing the notion of a
bound-state nucleon propagator, closed-form, analytic expressions for all
nuclear-structure functions are developed in terms of an accurately calibrated
relativistic mean-field model. Using a strange-quark contribution to the
axial-vector form factor of , a significant enhancement in the
proton-to-neutron yields is observed relative to one with .Comment: 23 pages, 12 figures, Revtex, Submitted to Phys. Rev.
Helicity asymmetries in neutrino-nucleus interactions
We investigate the helicity properties of the ejectile in quasi-elastic
neutrino-induced nucleon-knockout reactions and consider the 12C target as a
test case. A formalism based on a relativistic mean-field model is adopted. The
influence of final-state interactions is evaluated within a relativistic
multiple-scattering Glauber approximation (RMSGA) model. Our calculations
reveal that the helicity asymmetries A_l in A(\overline{\nu},\overline{\nu}'N)
processes are extremely sensitive to strange-quark contributions to the weak
vector form-factors. Thereby, nuclear corrections, such as final-state
interactions and off-shell ambiguities in the electroweak current operators,
are observed to be of marginal importance. This facilitates extracting
strange-quark information from the helicity asymmetry A_l.Comment: 14 pages, 6 figures, 1 table submitted to PL
Direct Test of the Scalar-Vector Lorentz Structure of the Nucleon- and Antinucleon-Nucleus Potential
Quantum Hadrodynamics in mean field approximation describes the effective
nucleon-nucleus potential (about -50 MeV deep) as resulting from a strong
repulsive vector (about 400 MeV) and a strong attractive scalar (about -450
MeV) contribution. This scalar-vector Lorentz structure implies a significant
lowering of the threshold for photoproduction on a nucleus by about
850 MeV as compared to the free case since charge conjugation reverses the sign
of the vector potential contribution in the equation of motion for the
states. It also implies a certain size of the photon induced
pair creation cross section near threshold which is calculated for a
target nucleus Pb. We also indicate a measurable second signature of
the photoproduction process by estimating the increased cross
section for emission of charged pions as a consequence of
annihilation within the nucleus.Comment: 18 pages latex, 5 PS figure
Effects of the triaxial deformation and pairing correlation on the proton emitter 145Tm
The ground-state properties of the recent reported proton emitter 145Tm have
been studied within the axially or triaxially deformed relativistic mean field
(RMF) approaches, in which the pairing correlation is taken into account by the
BCS-method with a constant pairing gap. It is found that triaxiality and
pairing correlations play important roles in reproducing the experimental one
proton separation energy. The single-particle level, the proton emission orbit,
the deformation parameters beta = 0.22 and gamma = 28.98 and the corresponding
spectroscopic factor for 145Tm in the triaxial RMF calculation are given as
well.Comment: 17 pages, 7 figures and 1 table. accepted by Physical Review
Relativistic models for quasi-elastic neutrino scattering
We present quasi-elastic neutrino-nucleus cross sections in the energy range
from 150 MeV up to 5 GeV for the target nuclei 12C and 56Fe. A relativistic
description of the nuclear dynamics and the neutrino-nucleus coupling is
adopted. For the treatment of final-state interactions (FSI) we rely on two
frameworks succesfully applied to exclusive electron-nucleus scattering: a
relativistic optical potential and a relativistic multiple-scattering Glauber
approximation. At lower energies, the optical-potential approach is considered
to be the optimum choice, whereas at high energies a Glauber approach is more
natural. Comparing the results of both calculations, it is found that the
Glauber approach yields valid results down to the remarkably small nucleon
kinetic energies of 200 MeV. We argue that the nuclear transparencies extracted
from A(e,e'p) measurements can be used to obtain realistic estimates of the
effect of FSI mechanisms on quasi-elastic neutrino-nucleus cross sections. We
present two independent relativistic plane-wave impulse approximation (RPWIA)
calculations of quasi-elastic neutrino-nucleus cross sections. They agree at
the percent level, showing the reliability of the numerical techniques adopted
and providing benchmark RPWIA results.Comment: revised version,28 pages, 7 figures, accepted in Phys.Rev.
Pygmy dipole resonance as a constraint on the neutron skin of heavy nuclei
The isotopic dependence of the isovector Pygmy dipole response in tin is
studied within the framework of the relativistic random phase approximation.
Regarded as an oscillation of the neutron skin against the isospin-symmetric
core, the pygmy dipole resonance may place important constraints on the neutron
skin of heavy nuclei and, as a result, on the equation of state of neutron-rich
matter. The present study centers around two questions. First, is there a
strong correlation between the development of a neutron skin and the emergence
of low-energy isovector dipole strength? Second, could one use the recently
measured Pygmy dipole resonance in 130Sn and 132Sn to discriminate among
theoretical models? For the first question we found that while a strong
correlation between the neutron skin and the Pygmy dipole resonance exists, a
mild anti-correlation develops beyond 120Sn. The answer to the second question
suggests that models with overly large neutron skins--and thus stiff symmetry
energies--are in conflict with experiment.Comment: 16 pages with 6 figure
Candidate MKiD nucleus 106Rh in triaxial relativistic mean-field approach with time-odd fields
The configuration-fixed constrained triaxial relativistic mean-field approach
is extended by including time-odd fields and applied to study the candidate
multiple chiral doublets (MKiD) nucleus 106Rh. The energy contribution from
time-odd fields and microscopical evaluation of center-of-mass correction as
well as the modification of triaxial deformation parameters beta, gamma due to
the time-odd fields are investigated. The contributions of the time-odd fields
to the total energy are 0.1-0.3 MeV and they modify slightly the gamma values.
However, the previously predicted multiple chiral doublets still exist.Comment: 9 pages, 3 figures, accepted for publication as a Brief Report in
Physical Review
Time-odd triaxial relativistic mean field approach for nuclear magnetic moments
The time-odd triaxial relativistic mean field approach is developed and
applied to the investigation of the ground-state properties of light odd-mass
nuclei near the double-closed shells. The nuclear magnetic moments including
the isoscalar and isovector ones are calculated and good agreement with Schmidt
values is obtained. Taking F as an example, the splitting of the single
particle levels (around MeV near the Fermi level), the nuclear current,
the core polarizations, and the nuclear magnetic potential, i.e., the spatial
part of the vector potential, due to the violation of the time reversal
invariance are investigated in detail.Comment: 26 pages, 8 figures. PHYSICAL REVIEW C (accepted
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