The structure of low-energy collective states in proton-deficient N=28
isotones is analyzed using structure models based on the relativistic energy
density functional DD-PC1. The relativistic Hartree-Bogoliubov model for
triaxial nuclei is used to calculate binding energy maps in the
β-γ plane. The evolution of neutron and proton single-particle
levels with quadrupole deformation, and the occurrence of gaps around the Fermi
surface, provide a simple microscopic interpretation of the onset of
deformation and shape coexistence. Starting from self-consistent constrained
energy surfaces calculated with the functional DD-PC1, a collective Hamiltonian
for quadrupole vibrations and rotations is employed in the analysis of
excitation spectra and transition rates of 46Ar, 44S, and 42Si.
The results are compared to available data, and previous studies based either
on the mean-field approach or large-scale shell-model calculations. The present
study is particularly focused on 44S, for which data have recently been
reported that indicate pronounced shape coexistence.Comment: 31 pages, 11 figures. arXiv admin note: text overlap with
arXiv:1102.419