Isobaric multiplet yrast energies and isospin non-conserving forces

The isovector and isotensor energy differences between yrast states of isobaric multiplets in the lower half of the $pf$ region are quantitatively reproduced in a shell model context. The isospin non-conserving nuclear interactions are found to be at least as important as the Coulomb potential. Their isovector and isotensor channels are dominated by J=2 and J=0 pairing terms, respectively. The results are sensitive to the radii of the states, whose evolution along the yrast band can be accurately followed.Comment: 4 pages, 4 figures. Superseeds second part of nucl-th/010404

The isovector effective charge and the staggering of the 2+ to 0+ transition probabilities in the Titanium isotopes

In an effort to understand the magical status of N=32 and N=34 at the very neutron rich edge, experiments have been carried out in the Titanium isotopes up to A=56. The measured staggering of the B(E2)'s is not reproduced by the shell model calculations using the best effective interactions. We argue that this may be related to the choice of the isovector effective charge and to the value of the N=34 neutron gap.Comment: 2 pages, 2 figure

Advanced density matrix renormalization group method for nuclear structure calculations

We present an efficient implementation of the Density Matrix Renormalization Group (DMRG) algorithm that includes an optimal ordering of the proton and neutron orbitals and an efficient expansion of the active space utilizing various concepts of quantum information theory. We first show how this new DMRG methodology could solve a previous $400$ KeV discrepancy in the ground state energy of $^{56}$Ni. We then report the first DMRG results in the $pf+g9/2$ shell model space for the ground $0^+$ and first $2^+$ states of $^{64}$Ge which are benchmarked with reference data obtained from Monte Carlo shell model. The corresponding correlation structure among the proton and neutron orbitals is determined in terms of the two-orbital mutual information. Based on such correlation graphs we propose several further algorithmic improvement possibilities that can be utilized in a new generation of tensor network based algorithms.Comment: 5 pages, 4 figure

Shape Coexistence in 78 Ni and the new Island of Inversion

Large Scale Shell Model calculations (SM-CI) predict that the region of deformation which comprises the heaviest Chromium and Iron isotopes at and beyond N=40 will merge with a new one at N=50 in an astonishing parallel to the N=20 and N=28 case in the Neon and Magnesium isotopes. We propose a valence space including the full pf-shell for the protons and the full sdg shell for the neutrons; which represents a comeback of the the harmonic oscillator shells in the very neutron rich regime. The onset of deformation is understood in the framework of the algebraic SU3-like structures linked to quadrupole dominance. Our calculations preserve the doubly magic nature of the ground state of 78 Ni, which, however, exhibits a well deformed prolate band at low excitation energy, providing a striking example of shape coexistence far from stability

Nilsson-SU3 self-consistency in heavy N=Z nuclei

It is argued that there exist natural shell-model spaces optimally adapted to the operation of two variants of Elliott's SU3 symmetry that provide accurate predictions of quadrupole moments of deformed states. A self-consistent Nilsson-like calculation describes the competition between the realistic quadrupole force and the central field, indicating a remarkable stability of the quadrupole moments - which remain close to their quasi- and pseudo-SU3 values - as the single-particle splittings increase. A detailed study of the N=Z even nuclei from Ni56 to Cd96 reveals that the region of prolate deformation is bounded by a pair of transitional nuclei Kr72 and Mo84 in which prolate ground-state bands are predicted to dominate, though coexisting with oblate onesThis work is partly supported by Spanish Grants No. FPA2011-29854 from MICINN and No. SEV-2012-0249 from MINECO, Centro de Excelencia Severo Ochoa Programm

A Shell Model Description of the Decay Out of the Super-Deformed Band of 36Ar

Large scale shell model calculations in two major oscillator shells (sd and pf) describe simultaneously the super-deformed excited band of 36Ar and its low-lying states of dominant sd character. In addition, several two particle two hole states and a side band of negative parity are also well reproduced. We explain the appearance of the super-deformed band at such low excitation energy as a consequence of the very large correlation energy of the configurations with many particles and many holes (np-nh) relative to the normal filling of the spherical mean field orbits (0p-0h). We study the mechanism of mixing between these different configurations, to understand why the super-deformed band survives and how it finally decays into the low-lying sd-dominated states via the indirect mixing of the 0p-0h and 4p-4h configurations.Comment: 4 pages 5 figures, revtex4, revised version, minor change

The land of deformation south of 68^{68}Ni

We study the development of collectivity in the neutron-rich nuclei around $N=40$, where experimental and theoretical evidences suggest a rapid shape change from the spherical to the rotational regime, in analogy to what happens at the {\it island of inversion} surrounding $^{31}$Na. Theoretical calculations are performed within the interacting shell model framework in a large valence space, based on a $^{48}$Ca core which encompasses the full $pf$ shell for the protons and the $0f_{5/2}$, $1p_{3/2}$, $1p_{1/2}$, $0g_{9/2}$ and $1d_{5/2}$ orbits for the neutrons. The effective interaction is based on a G-matrix obtained from a realistic nucleon-nucleon potential whose monopole part is corrected empirically to produce effective single particle energies compatible with the experimental data. We find a good agreement between the theoretical results and the available experimental data. We predict the onset of deformation at different neutron numbers for the various isotopic chains. The maximum collectivity occurs in the chromium isotopes, where the large deformation regime starts already at $N=38$. The shell evolution responsible for the observed shape changes is discussed in detail, in parallel to the situation in the $N=20$ region

Spherical Shell Model description of rotational motion

Exact diagonalizations with a realistic interaction show that configurations with four neutrons in a major shell and four protons in another -or the same- major shell, behave systematically as backbending rotors. The dominance of the $q\cdot q$ component of the interaction is explained by an approximate form of SU3 symmetry. It is suggested that these configurations are associated with the onset of rotational motion in medium and heavy nuclei.Comment: 7 pages, RevTeX 3.0 using psfig, 6 Postscript figures included using uufile