Microscopic linear response calculations based on the Skyrme functional plus the pairing contribution

A self-consistent Quasiparticle-Random-Phase-Approximation (QRPA) model which employs the canonical Hartree-Fock-Bogoliubov (HFB) basis and an energy-density functional with a Skyrme mean field part and a density-dependent pairing, is used to study the monopole collective excitations of spherical even-even nuclei. The influence of the spurious state on the strength function of the isoscalar monopole excitations is clearly assessed. We compare the effect of different kinds of pairing forces (volume pairing, surface pairing and mixed pairing) on the monopole excitation strength function. The energy of the Isoscalar Giant Monopole Resonance (ISGMR), which is related to the nuclear incompressibility $K_{\infty}$, is calculated for tin isotopes and the results are discussed.Comment: Accepted for publication in Phys. Rev.

Gamow-Teller response and its spreading mechanism in doubly magic nuclei

The scope of the paper is to apply a state-of-the-art beyond mean-field model to the description of the Gamow-Teller response in atomic nuclei. This topic recently attracted considerable renewed interest, due, in particular, to the possibility of performing experiments in unstable nuclei. We study the cases of $^{48}$Ca, $^{78}$Ni, $^{132}$Sn and $^{208}$Pb. Our model is based on a fully self-consistent Skyrme Hartree-Fock plus random phase approximation. The same Skyrme interaction is used to calculate the coupling between particles and vibrations, which leads to the mixing of the Gamow-Teller resonance with a set of doorway states and to its fragmentation. We compare our results with available experimental data. The microscopic coupling mechanism is also discussed in some detail.Comment: 27 pages, 10 figure

Orbital-free Density Functional Theory: differences and similarities between electronic and nuclear systems

Orbital-free Density Functional Theory (OF-DFT) has been used when studying atoms, molecules and solids. In nuclear physics, there has been basically no application of OF-DFT so far, as the Density Functional Theory (DFT) has been widely applied to the study of many nuclear properties mostly within the Kohn-Sham (KS) scheme. There are many realizations of nuclear KS-DFT, but computations become very demanding for heavy systems, such as superheavy nuclei and the inner crust of neutron stars, and it is hard to describe exotic nuclear shapes using a finite basis made with a limited number of orbitals. These bottlenecks could, in principle, be overcome by an orbital-free formulation of DFT. This work is a first step towards the application of OF-DFT to nuclei. In particular, we have implemented possible choices for an orbital-free kinetic energy and solved the associated Schr\"odinger equation either with simple potentials or with simplified nuclear density functionals. While the former choice sheds light on the differences between electronic and nuclear systems, the latter choice allows us discussing the practical applications to nuclei and the open questions.Comment: Submitted for publicatio

The Gamow-Teller response within Skyrme random-phase approximation plus particle-vibration coupling

Although many random-phase approximation (RPA) calculations of the Gamow-Teller (GT) response exist, this is not the case for calculations going beyond the mean-field approximation. We apply a consistent model that includes the coupling of the GT resonance to low-lying vibrations, to nuclei of the $fp$ shell. Among other motivations, our goal is to see if the particle-vibration coupling can redistribute the low-lying GT$^+$ strength that is relevant for electron-capture processes in core-collapse supernova. We conclude that the lowering and fragmentation of that strength are consistent with the experimental findings and validate our model. However, the particle-vibration coupling cannot account for the quenching of the total value of the low-lying strength.Comment: 25 pages, 10 figure

Gamow-Teller strength distributions of 18O and well-deformed nuclei 24,26Mg by deformed QRPA

We investigate the Gamow-Teller (GT) transition strength distributions of {strongly} deformed nuclei, $^{24,26}$Mg, as well as of $^{18}$O. The calculations are performed within a deformed quasi-particle random phase approximation (DQRPA) which explicitly includes the deformation degree of freedom in the Skyrme-Hartree-Fock (SHF) and RPA calculations. The residual particle-particle ($p-p$) interaction as well as the particle-hole ($p-h$) interaction are extracted from Br\"uckner $G$-matrix calculations. The {residual interaction} dependence of the low-lying GT strength of these strongly deformed nuclei is examined by changing the strength of the residual $p-p$ and $p-h$ interactions. We have found that the low-lying GT peaks are quite similar in energy to those found in {spherical} $N=Z$ and $N=Z+2$ nuclei near magic shells, but the configurations {of $^{24,26}$Mg are largely mixed by} the pairing correlations and the deformation. Our results are compared to the experimental GT $(\pm)$ transition data by ($t$, $^3$He) and ($^{3}$He, $t$) reactions, {and found to reproduce the main features of GT strength distributions.Comment: 25 pages, 23 figure

Nuclear incompressibility from spherical and deformed nuclei

We present an analysis based on the deformed Quasi Particle Random Phase Approximation, on top of a deformed Hartree-Fock-Bogoliubov description of the ground state, aimed at studying the isoscalar monopole and quadrupole response in a deformed nucleus. This analysis is motivated by the need of understanding the coupling between the two modes and how it might affect the extraction of the nuclear incompressibility from the monopole distribution. After discussing this motivation, we present the main ingredients of our theoretical framework, and we show some results obtained with the SLy4 and SkM* interactions for the nucleus 24Mg

Nuclear matter incompressibility coefficient in relativistic and nonrelativistic microscopic models

We systematically analyze the recent claim that nonrelativistic and relativistic mean field (RMF) based random phase approximation (RPA) calculations for the centroid energy E_0 of the isoscalar giant monopole resonance yield for the nuclear matter incompressibility coefficient, K_{nm}, values which differ by about 20%. For an appropriate comparison with the RMF based RPA calculations, we obtain the parameters for the Skyrme force used in the nonrelativistic model by adopting the same procedure as employed in the determination of the NL3 parameter set of an effective Lagrangian used in the RMF model. Our investigation suggest that the discrepancy between the values of K_{nm} predicted by the relativistic and nonrelativistic models is significantly less than 20%.Comment: Revtex file (13 pages), appearing in PRC-Rapid Com

Possible inconsistency between phenomenological and theoretical determinations of charge symmetry breaking in nuclear energy density functionals

We summarize the recent progress on the determination of the charge symmetry breaking term of nuclear energy density functionals. We point out that the strength of the term determined theoretically is remarkably smaller than that determined phenomenologically, which is still an open question