1,721,081 research outputs found
Critical assessment of mean field models based on effective interactions
No full textMean field schemes, from simple Hartree–Fock plus random phase approximation calculations
of the ground and excited states to more sophisticated approaches which include pairing as well, have been
popular for quite a long time. In these models, the input is an effective interaction. We still lack a precise
link between this interaction and a more fundamental theory; however, there have been various new recent
attempts to correlate empirical pieces of evidence about nuclear (and neutron) matter, or experimental
results, with the properties of the effective interactions. In this contribution, we claim that, while we have
indeed made some progress in our understanding of certain features of the interactions, we are still missing
a clue about its proper density dependence and about its isovector properties
Constraints, limits and extensions for nuclear energy density functionals
No full textIn the present contribution, we discuss the behavior of Skyrme forces when they are employed to study both neutron stars and giant resonance states in 208Pb within the fully self-consistent Random Phase Approximation (RPA). We point out that clear correlations exist between the results for the isoscalar monopole and isovector dipole resonances (ISGMR and IVGDR), and definite quantities which characterize the equation of state (EOS) of uniform matter. We propose that the RPA results or, to some extent, the mentioned EOS parameters, are used as constraints when a force is fitted. This suggestion can be valid also when the fit of a more general energy density functional is envisaged. We use our considerations to select a limited number of Skyrme forces (10) out of a large sample of 78 interactions
The symmetry energy and other open questions concerning effective functionals
No full textThe nuclear structure community is striving to determine a nuclear energy functional which is as universal and as accurate as possible. When a functional is determined by fitting free parameters, the constraints on these parameters coming from excited states (like the well-known giant resonances) are not, as a rule, imposed. This work shows that at least three constraints could be imposed on Skyrme functionals, by explaining the physical background and discussing their relevance
The inclusion of tensor terms in the nonrelativistic nuclear energy density functionals
No full textThis contribution is intended to briefly review recent attempts to include tensor terms in effective nuclear Energy Density Functionals (EDFs). We stress that effective tensor forces should not be conflused with the well-known bare tensor force. Consistently with the basic idea of EDFs, collective states are shown to provide better constraints for the tensor parameters, as compared with single-particle states. In fact, basic limitations of the description of the single-particle strength in atomic nuclei provided by EDFs, are highlighted in the last part of this contribution
Some open questions for microscopic nuclear structure models and hints for spectroscopic measurements
No full textThis contribution aims at updating the non-expert reader about the successes and the drawbacks of nuclear structure models which describe the ground-state properties. The main emphasis is on models based on Density Functional Theory (DFT), with a personal bias towards the nonrelativistic implementations. After a survey about ground-state masses and a short discussion on nuclear radii, it is argued that one of the most relevant open problems is the description of single-particle states and more generally of detailed spectroscopic properties. Overall (i. e., bulk) properties are easier to reproduce and thus, less capable to discriminate between competing theories. Accordingly, it is concluded that trap-assisted detailed spectroscopic measurements are the most useful in order to improve our understanding of nuclei
The compression modes in atomic nuclei and their relevance for the nuclear equation of state
No full textAccurate assessment of the value of the incompressibility coefficient, K-infinity of symmetric nuclear matter, which is directly related to the curvature of the equation of state (EOS), is needed to extend our knowledge of the EOS in the vicinity of the saturation point. We review the current status of K-infinity as determined from experimental data on isoscalar giant monopole and dipole resonances (compression modes) in nuclei by employing the microscopic theory based on the Random Phase Approximation (RPA). The importance of full self-consistent calculations is emphasized. In recent years, a comparision between RPA calculations based on either non-relativistic effective interactions or relativistic Lagrangians has been pursued in great detail. It has been pointed out that these two types of models embed different ansatz for the density dependence of the symmetry energy. This fact has consequences on the extraction of the nuclear incompressibility, as it is discussed. The comparison with other ways of extracting K-infinity from experimental data is highlighted
Spin-isospin nuclear response using the existing microscopic Skyrme functionals
No full textOur paper aims at providing an answer to the question of whether one can reliably describe the properties of the
most important spin-isospin nuclear excitations by using the available nonrelativistic Skyrme energy functionals.
Our method, which has been introduced in a previous publication devoted to the isobaric analog states, is the
self-consistent quasiparticle random-phase approximation (QRPA). The inclusion of pairing is instrumental for
describing a number of experimentally measured spherical systems which are characterized by open shells. We
discuss the effect of isoscalar and isovector pairing correlations. Based on the results for the Gamow-Teller
resonance in 90Zr, 208Pb, and a few Sn isotopes, we draw definite conclusions on the performance of different Skyrme parametrizations, and we suggest improvements for future fits. We also use the spin-dipole resonance as a benchmark of our statement
Tensor interaction in mean-field and density functional theory approaches to nuclear structure
No full textThe importance of the tensor force for nuclear structure has been
recognized long ago. Recently, the interest for this topic has been
revived by the study of the evolution of nuclear properties far from the
stability line. However, in the context of the effective theories that
describe medium-heavy nuclei, the role of the tensor force is still
debated. This review focuses on ground-state properties like masses and
deformation, on single-particle states, and on excited vibrational and
rotational modes. The goal is to assess which properties, if any, can
bring clear signatures of the tensor force within the mean-field or
density functional theory framework. It will be concluded that, while
evidences for a clear neutron proton tensor force exist despite
quantitative uncertainties, the role of the tensor force among equal
particles is less well established
Microscopic calculations of charge-exchange nuclear modes
No full textMicroscopic calculations of nuclear states excited by means of charge-exchange reactions and
involving spin and isospin degrees of freedom, in particular, of the Gamow–Teller and the spin–dipole
resonances, are discussed. The framework is a fully self-consistent nonrelativistic spherical quasiparticle
random-phase approximation constructed on top of the Hartree–Fock–Bardeen–Cooper–Schrieffer approach.
Our results are compared with available experimental data, and a critical discussion is attempted
Subtraction of the spurious translational mode from the RPA response function
No full textIt is well known that within self-consistent random-phase approximation (RPA) on top of Hartree-Fock (HF), the translational symmetry should be restored. Because of approximations at the level of the practical implementation, this restoration may be only partial. As a result, one has spurious contributions in the physical quantities that are extracted from RPA. Although there are several recipes in the literature to overcome this drawback to produce transition densities or strength functions that are free from spurious contamination, there is no formalism associated with the full RPA response function. We present such formalism in this paper. Our goal is to avoid spurious contamination when the response function is used in many-body frameworks like the particle-vibration coupling theory
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