The relativistic quasiparticle time blocking approximation (RQTBA), developed recently as a consi... more The relativistic quasiparticle time blocking approximation (RQTBA), developed recently as a consistent combination of the covariant energy density functional theory (CEDFT) and the modern extensions of the Landau– Migdal theory of finite fermi systems, is reviewed in Ref. [1]. In the RQTBA, starting from the covariant energy functional, phonon energies and their vertices are calculated without any further parameters. They form the basis of particle-vibrational coupling leading to an energy depe ndence of the self-energy and an induced energy-dependent interaction in the response equation. A proper subtraction of the static phonon coupling contribution from the induced interaction avoids double counting of this contribution. Applications in spherical nuclei show excellent agre ement with experimental data on nuclear spectra below 30 MeV. The theoretical description of nuclear low-lying dipole strength remains among the most important problems in nuclear structure and nuclear astrophysics. Modern measurements of the dipole strength resolve the fine structure of the spectra below the neutron threshold. This offers exciting opportunities for microscopic nuclear structure mo dels to describe the fine structure of the dipole spectra below the neutron threshold and to help in analyzing the experimental data. In nuclei with pronounced isospin asymmetry the lowlying dipole strength is characterized by the pygmy resonance which is a coherent oscillation of the isospin excess against the isospin saturated core. Since the pygmy dipole mode has essentially surface nature, it mixes with other sur face modes, especially with low-lying ones. This supposition has been confirmed by explicit RQTBA calculations. It has been found that the pygmy mode, arising in RQRPA as a single state or as very few low lying dipole states with isoscalar character, is strongly fragmented over many stat es in a broad energy region due to the coupling to phonons. As a result, some fraction of the strength is located well below the original position of the RQRPA pygmy mode. Compared to existing data, the RQTBA describes the total fraction of the dipole strength below the neutron threshold very reasonably. However, in order to account for the fine structure of the spectrum, more correlations should be included in the microscopic model. In particular, it has to reproduce the lowest dipole state in vibrational nuclei, whic h is identified as a member of the quintuplet [21 ⊗ 31 ]. A two-phonon version of the relativistic quasiparticle
The fully self-consistent relativistic quasiparticle random-phase approximation (RQRPA) has been ... more The fully self-consistent relativistic quasiparticle random-phase approximation (RQRPA) has been formulated in the the canonical basis of the relativistic Hartree-Bogoliubov (RHB) model and applied in the analysis of the isovector dipole response in nuclei with large neutron excess. The dipole response is characterized by the fragmentation of the strength distribution and its spreading into the low-energy region and by mixing of isoscalar and isovector modes. In light nuclei the onset of dipole strength in the low-energy region is due to single particle excitations of the loosely bound neutrons. In heavier nuclei, low-lying dipole states appear, which are characterized by a more distributed structure of the RQRPA amplitude. An analysis of the transition densities and velocity distributions in neutron rich N=82 isotones and tin isotopes reveals the dynamics of the dipole pygmy resonance: the vibration of the excess neutrons against the inert core composed of equal numbers of protons and neutrons.
Starting with an effective Hamiltonian for multi-quark systems, we propose a mapping of the quark... more Starting with an effective Hamiltonian for multi-quark systems, we propose a mapping of the quark degrees of freedom onto triplet fermions that represent colorless three-quark clusters. We end up with an effective Hamiltonian for the triplet fermions, which can be treated by traditional nuclear many-body techniques. In this approach, the nuclear ground state represents a quantum liquid of composite particles, the nucleons. Higher-lying states involve both excitations within the space of nucleons and excitations of the nucleons themselves. The method is tested in the context of a schematic model of quarks interacting through an angular momentum and isospin pairing interaction and is shown to be very promising.
Systematic calculations of the fission barriers with allowance of triaxial deformation have been ... more Systematic calculations of the fission barriers with allowance of triaxial deformation have been performed for the first time within the covariant density functional theory. Pairing is treated within the BCS approximation using seniority zero forces adjusted to empirical values of the gap ...
The Woods-Saxon basis has been suggested to replace the widely used harmonic oscillator basis for... more The Woods-Saxon basis has been suggested to replace the widely used harmonic oscillator basis for solving the relativistic mean field (RMF) theory in order to generalize it to study exotic nuclei. As examples, relativistic Hartree theory is solved for spherical nuclei in a Woods-Saxon basis obtained by solving either the Schrödinger equation or the Dirac equation (labelled as SRHSWS and SRHDWS, respectively and SRHWS for both). In SRHDWS, the negative levels in the Dirac Sea must be properly included. The basis in SRHDWS could be smaller than that in SRHSWS which will simplify the deformed problem. The results from SRHWS are compared in detail with those from solving the spherical relativistic Hartree theory in the harmonic oscillator basis (SRHHO) and those in the coordinate space (SRHR). All of these approaches give identical nuclear properties such as total binding energies and root mean square radii for stable nuclei. For exotic nuclei, e.g., ^72Ca, SRHWS satisfactorily reproduc...
Effects of the Fermi-sea polarization on the superfluidity in nuclear matter are studied in a fra... more Effects of the Fermi-sea polarization on the superfluidity in nuclear matter are studied in a framework of quantum hadrodynamics. The particle-hole polarization due to $\sigma$ and $\omega$ mesons enhances the peak value of the pairing gap contrary to the previous non-relativistic studies.
On the way of a microscopic derivation of covariant density functionals, the first complete solut... more On the way of a microscopic derivation of covariant density functionals, the first complete solution of the relativistic Brueckner-Hartree-Fock (RBHF) equations is presented for symmetric nuclear matter. In most of the earlier investigations, the G-matrix is calculated only in the space of positive energy solutions. On the other side, for the solution of the relativistic Hartree-Fock (RHF) equations, also the elements of this matrix connecting positive and negative energy solutions are required. So far, in the literature, these matrix elements are derived in various approximations. We discuss solutions of the Thompson equation for the full Dirac space and compare the resulting equation of state with those of earlier attempts in this direction.
The relativistic quasiparticle time blocking approximation (RQTBA), developed recently as a consi... more The relativistic quasiparticle time blocking approximation (RQTBA), developed recently as a consistent combination of the covariant energy density functional theory (CEDFT) and the modern extensions of the Landau– Migdal theory of finite fermi systems, is reviewed in Ref. [1]. In the RQTBA, starting from the covariant energy functional, phonon energies and their vertices are calculated without any further parameters. They form the basis of particle-vibrational coupling leading to an energy depe ndence of the self-energy and an induced energy-dependent interaction in the response equation. A proper subtraction of the static phonon coupling contribution from the induced interaction avoids double counting of this contribution. Applications in spherical nuclei show excellent agre ement with experimental data on nuclear spectra below 30 MeV. The theoretical description of nuclear low-lying dipole strength remains among the most important problems in nuclear structure and nuclear astrophysics. Modern measurements of the dipole strength resolve the fine structure of the spectra below the neutron threshold. This offers exciting opportunities for microscopic nuclear structure mo dels to describe the fine structure of the dipole spectra below the neutron threshold and to help in analyzing the experimental data. In nuclei with pronounced isospin asymmetry the lowlying dipole strength is characterized by the pygmy resonance which is a coherent oscillation of the isospin excess against the isospin saturated core. Since the pygmy dipole mode has essentially surface nature, it mixes with other sur face modes, especially with low-lying ones. This supposition has been confirmed by explicit RQTBA calculations. It has been found that the pygmy mode, arising in RQRPA as a single state or as very few low lying dipole states with isoscalar character, is strongly fragmented over many stat es in a broad energy region due to the coupling to phonons. As a result, some fraction of the strength is located well below the original position of the RQRPA pygmy mode. Compared to existing data, the RQTBA describes the total fraction of the dipole strength below the neutron threshold very reasonably. However, in order to account for the fine structure of the spectrum, more correlations should be included in the microscopic model. In particular, it has to reproduce the lowest dipole state in vibrational nuclei, whic h is identified as a member of the quintuplet [21 ⊗ 31 ]. A two-phonon version of the relativistic quasiparticle
The fully self-consistent relativistic quasiparticle random-phase approximation (RQRPA) has been ... more The fully self-consistent relativistic quasiparticle random-phase approximation (RQRPA) has been formulated in the the canonical basis of the relativistic Hartree-Bogoliubov (RHB) model and applied in the analysis of the isovector dipole response in nuclei with large neutron excess. The dipole response is characterized by the fragmentation of the strength distribution and its spreading into the low-energy region and by mixing of isoscalar and isovector modes. In light nuclei the onset of dipole strength in the low-energy region is due to single particle excitations of the loosely bound neutrons. In heavier nuclei, low-lying dipole states appear, which are characterized by a more distributed structure of the RQRPA amplitude. An analysis of the transition densities and velocity distributions in neutron rich N=82 isotones and tin isotopes reveals the dynamics of the dipole pygmy resonance: the vibration of the excess neutrons against the inert core composed of equal numbers of protons and neutrons.
Starting with an effective Hamiltonian for multi-quark systems, we propose a mapping of the quark... more Starting with an effective Hamiltonian for multi-quark systems, we propose a mapping of the quark degrees of freedom onto triplet fermions that represent colorless three-quark clusters. We end up with an effective Hamiltonian for the triplet fermions, which can be treated by traditional nuclear many-body techniques. In this approach, the nuclear ground state represents a quantum liquid of composite particles, the nucleons. Higher-lying states involve both excitations within the space of nucleons and excitations of the nucleons themselves. The method is tested in the context of a schematic model of quarks interacting through an angular momentum and isospin pairing interaction and is shown to be very promising.
Systematic calculations of the fission barriers with allowance of triaxial deformation have been ... more Systematic calculations of the fission barriers with allowance of triaxial deformation have been performed for the first time within the covariant density functional theory. Pairing is treated within the BCS approximation using seniority zero forces adjusted to empirical values of the gap ...
The Woods-Saxon basis has been suggested to replace the widely used harmonic oscillator basis for... more The Woods-Saxon basis has been suggested to replace the widely used harmonic oscillator basis for solving the relativistic mean field (RMF) theory in order to generalize it to study exotic nuclei. As examples, relativistic Hartree theory is solved for spherical nuclei in a Woods-Saxon basis obtained by solving either the Schrödinger equation or the Dirac equation (labelled as SRHSWS and SRHDWS, respectively and SRHWS for both). In SRHDWS, the negative levels in the Dirac Sea must be properly included. The basis in SRHDWS could be smaller than that in SRHSWS which will simplify the deformed problem. The results from SRHWS are compared in detail with those from solving the spherical relativistic Hartree theory in the harmonic oscillator basis (SRHHO) and those in the coordinate space (SRHR). All of these approaches give identical nuclear properties such as total binding energies and root mean square radii for stable nuclei. For exotic nuclei, e.g., ^72Ca, SRHWS satisfactorily reproduc...
Effects of the Fermi-sea polarization on the superfluidity in nuclear matter are studied in a fra... more Effects of the Fermi-sea polarization on the superfluidity in nuclear matter are studied in a framework of quantum hadrodynamics. The particle-hole polarization due to $\sigma$ and $\omega$ mesons enhances the peak value of the pairing gap contrary to the previous non-relativistic studies.
On the way of a microscopic derivation of covariant density functionals, the first complete solut... more On the way of a microscopic derivation of covariant density functionals, the first complete solution of the relativistic Brueckner-Hartree-Fock (RBHF) equations is presented for symmetric nuclear matter. In most of the earlier investigations, the G-matrix is calculated only in the space of positive energy solutions. On the other side, for the solution of the relativistic Hartree-Fock (RHF) equations, also the elements of this matrix connecting positive and negative energy solutions are required. So far, in the literature, these matrix elements are derived in various approximations. We discuss solutions of the Thompson equation for the full Dirac space and compare the resulting equation of state with those of earlier attempts in this direction.
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Papers by Peter Ring