5,980 research outputs found
Relativistic mean-field description of the dynamics of giant resonances
The relativistic mean-field theory provides a framework in which the nuclear
many-body problem is described as a self-consistent system of nucleons and
mesons. In the mean-field approximation, the self-consistent time evolution of
the nuclear system describes the dynamics of collective motion: nuclear
compressibility from monopole resonances, regular and chaotic dynamics of
isoscalar and isovector collective vibrations.Comment: LaTeX, 10 pages, 5 figures, Invited Talk, Topical Conference on Giant
resonances, Varenna, May 1998, to be published in Nucl. Phys.
Renormalized relativistic Hartree-Bogoliubov equations with a zero-range pairing interaction
A recently introduced scheme for the renormalization of the
Hartree-Fock-Bogoliubov equations in the case of zero-range pairing interaction
is extended to the relativistic Hartree-Bogoliubov model. A density-dependent
strength parameter of the zero-range pairing is adjusted in such a way that the
renormalization procedure reproduces the empirical pairing gap in
isospin-symmetric nuclear matter. The model is applied to the calculation of
ground-state pairing properties of finite spherical nuclei.Comment: 13 pages, 8 figures, accepted for publication in Physical Review
The Proton Electric Pygmy Dipole Resonance
The evolution of the low-lying E1 strength in proton-rich nuclei is analyzed
in the framework of the self-consistent relativistic Hartree-Bogoliubov (RHB)
model and the relativistic quasiparticle random-phase approximation (RQRPA).
Model calculations are performed for a series of N=20 isotones and Z=18
isotopes. For nuclei close to the proton drip-line, the occurrence of
pronounced dipole peaks is predicted in the low-energy region below 10 MeV
excitation energy. From the analysis of the proton and neutron transition
densities and the structure of the RQRPA amplitudes, it is shown that these
states correspond to the proton pygmy dipole resonance.Comment: 7 pages, 4 figures, to be published in Phys. Rev. Let
Beyond the relativistic Hartree mean-field approximation: energy dependent effective mass
The standard relativistic mean-field model is extended by including dynamical
effects that arise in the coupling of single-nucleon motion to collective
surface vibrations. A phenomenological scheme, based on a linear ansatz for the
energy dependence of the scalar and vector components of the nucleon
self-energy for states close to the Fermi surface, allows a simultaneous
description of binding energies, radii, deformations and single-nucleon spectra
in a self-consistent relativistic framework. The model is applied to the
spherical, doubly closed-shell nuclei 132Sn and 208Pb.Comment: 14 pages, 2 figures; replaced with revised versio
Random-phase approximation based on relativistic point-coupling models
The matrix equations of the random-phase approximation (RPA) are derived for
the point-coupling Lagrangian of the relativistic mean-field (RMF) model. Fully
consistent RMF plus (quasiparticle) RPA illustrative calculations of the
isoscalar monopole, isovector dipole and isoscalar quadrupole response of
spherical medium-heavy and heavy nuclei, test the phenomenological effective
interactions of the point-coupling RMF model. A comparison with experiment
shows that the best point-coupling effective interactions accurately reproduce
not only ground-state properties, but also data on excitation energies of giant
resonances.Comment: 24 pages, 4 figures, accepted for publication in Physical Review
Propagation-invariant beams with quantum pendulum spectra: from Bessel beams to Gaussian beam-beams
We describe a new class of propagation-invariant light beams with Fourier
transform given by an eigenfunction of the quantum mechanical pendulum. These
beams, whose spectra (restricted to a circle) are doubly-periodic Mathieu
functions in azimuth, depend on a field strength parameter. When the parameter
is zero, pendulum beams are Bessel beams, and as the parameter approaches
infinity, they resemble transversely propagating one-dimensional Gaussian
wavepackets (Gaussian beam-beams). Pendulum beams are the eigenfunctions of an
operator which interpolates between the squared angular momentum operator and
the linear momentum operator. The analysis reveals connections with Mathieu
beams, and insight into the paraxial approximation.Comment: 4 pages, 3 figures, Optics Letters styl
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