48 research outputs found
Optimizing the relativistic energy density functional with nuclear ground state and collective excitation properties
We introduce a new relativistic energy density functional constrained by the
ground state properties of atomic nuclei along with the isoscalar giant
monopole resonance energy and dipole polarizability in Pb. A unified
framework of the relativistic Hartree-Bogoliubov model and random phase
approximation based on the relativistic density-dependent point coupling
interaction is established in order to determine the DD-PCX parameterization by
minimization. This procedure is supplemented with the co-variance
analysis in order to estimate statistical uncertainties in the model parameters
and observables. The effective interaction DD-PCX accurately describes the
nuclear ground state properties including the neutron-skin thickness, as well
as the isoscalar giant monopole resonance excitation energies and dipole
polarizabilities. The implementation of the experimental data on nuclear
excitations allows constraining the symmetry energy close to the saturation
density, and the incompressibility of nuclear matter by using genuine
observables on finite nuclei in the minimization protocol, rather than
using pseudo-observables on the nuclear matter, or by relying on the ground
state properties only, as it has been customary in the previous studies.Comment: 6 pages, 3 figures, submitted to Physical Review
Large-scale calculations of supernova neutrino-induced reactions in Z=8-82 target nuclei
Background: In the environment of high neutrino-fluxes provided in
core-collapse supernovae or neutron star mergers, neutrino-induced reactions
with nuclei contribute to the nucleosynthesis processes. A number of
terrestrial neutrino detectors are based on inelastic neutrino-nucleus
scattering and modeling of the respective cross sections allow predictions of
the expected detector reaction rates.
Purpose: To provide a self-consistent microscopic description of
neutrino-nucleus cross sections involving a large pool of Z = 8 - 82 nuclei for
the implementation in models of nucleosynthesis and neutrino detector
simulations.
Methods: Self-consistent theory framework based on relativistic nuclear
energy density functional is employed to determine the nuclear structure of the
initial state and relevant transitions to excited states induced by neutrinos.
The weak neutrino-nucleus interaction is employed in the current-current form
and a complete set of transition operators is taken into account.
Results: We perform large-scale calculations of charged-current
neutrino-nucleus cross sections, including those averaged over supernova
neutrino fluxes, for the set of even-even target nuclei from oxygen toward lead
(Z = 8 - 82), spanning N = 8 - 182 (OPb pool). The model calculations include
allowed and forbidden transitions up to J = 5 multipoles.
Conclusions: The present analysis shows that the self-consistent calculations
result in considerable differences in comparison to previously reported cross
sections, and for a large number of target nuclei the cross sections are
enhanced. Revision in modeling r-process nucleosynthesis based on a
self-consistent description of neutrino-induced reactions would allow an
updated insight into the origin of elements in the Universe and it would
provide the estimate of uncertainties in the calculated element abundance
patterns.Comment: 25 pages, 12 figures, submitted to Physical Review
Inclusive charged-current neutrino-nucleus reactions calculated with the relativistic quasiparticle random phase approximation
Inclusive neutrino-nucleus cross sections are calculated using a consistent
relativistic mean-field theoretical framework. The weak lepton-hadron
interaction is expressed in the standard current-current form, the nuclear
ground state is described with the relativistic Hartree-Bogoliubov model, and
the relevant transitions to excited nuclear states are calculated in the
relativistic quasiparticle random phase approximation. Illustrative test
calculations are performed for charged-current neutrino reactions on C,
O, Fe, and Pb, and results compared with previous studies
and available data. Using the experimental neutrino fluxes, the averaged cross
sections are evaluated for nuclei of interest for neutrino detectors. We
analyze the total neutrino-nucleus cross sections, and the evolution of the
contribution of the different multipole excitations as a function of neutrino
energy. The cross sections for reactions of supernova neutrinos on O and
Pb target nuclei are analyzed as functions of the temperature and
chemical potential.Comment: 28 pages, 8 figures, 2 tables, submitted to Phys. Rev.
Neutron star structure and collective excitations of finite nuclei
We study relationships between properties of collective excitations in finite
nuclei and the phase transition density and pressure at the inner
edge separating the liquid core and the solid crust of a neutron star. A
theoretical framework that includes the thermodynamic method, relativistic
nuclear energy density functionals and the quasiparticle random-phase
approximation is employed in a self-consistent calculation of and
collective excitations in nuclei. The covariance analysis shows that properties
of charge-exchange dipole transitions, isovector giant dipole and quadrupole
resonances and pygmy dipole transitions are correlated with the core-crust
transition density and pressure. A set of relativistic nuclear energy density
functionals, characterized by systematic variation of the density dependence of
the symmetry energy of nuclear matter, is used to constrain possible values for
. By comparing the calculated excitation energies of giant
resonances, energy weighted pygmy dipole strength, and dipole polarizability
with available data, we obtain the weighted average values: fm and MeV fm.Comment: 4 pages, 3 figures, paper submitted for publicatio
Benchmarking nuclear models for Gamow-Teller response
A comparative study of the nuclear Gamow-Teller response (GTR) within
conceptually different state-of-the-art approaches is presented. Three nuclear
microscopic models are considered: (i) the recently developed charge-exchange
relativistic time blocking approximation (RTBA) based on the covariant density
functional theory, (ii) the shell model (SM) with an extended "jj77" model
space and (iii) the non-relativistic quasiparticle random-phase approximation
(QRPA) with a Brueckner G-matrix effective interaction. We study the physics
cases where two or all three of these models can be applied. The Gamow-Teller
response functions are calculated for 208-Pb, 132-Sn and 78-Ni within both RTBA
and QRPA. The strengths obtained for 208-Pb are compared to data that enables a
firm model benchmarking. For the nucleus 132-Sn, also SM calculations are
performed within the model space truncated at the level of a particle-hole (ph)
coupled to vibration configurations. This allows a consistent comparison to the
RTBA where ph+phonon coupling is responsible for the spreading width and
considerable quenching of the GTR. Differences between the models and
perspectives of their future developments are discussed.Comment: 9 pages, 2 figures, 1 table; to be published in Phys. Lett.
The Role of Fission in Neutron Star Mergers and Its Impact on the r-Process Peaks
Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations, we can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model, the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral, and the Hartree-Fock-Bogoliubov mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium is no longer maintained. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.Peer reviewe
Relativistic QRPA calculation of muon capture rates
The relativistic proton-neutron quasiparticle random phase approximation
(PN-RQRPA) is applied in the calculation of total muon capture rates on a large
set of nuclei from C to Pu, for which experimental values are
available. The microscopic theoretical framework is based on the Relativistic
Hartree-Bogoliubov (RHB) model for the nuclear ground state, and transitions to
excited states are calculated using the PN-RQRPA. The calculation is fully
consistent, i.e., the same interactions are used both in the RHB equations that
determine the quasiparticle basis, and in the matrix equations of the PN-RQRPA.
The calculated capture rates are sensitive to the in-medium quenching of the
axial-vector coupling constant. By reducing this constant from its free-nucleon
value by 10% for all multipole transitions, the calculation
reproduces the experimental muon capture rates to better than 10% accuracy.Comment: 19 pages, 5 figures, submitted to Phys. Rev.