Generalized seniority with realistic interactions in open-shell nuclei

TL;DR

This paper evaluates the generalized seniority scheme in nuclear shell models for open-shell nuclei, showing it can reduce computational complexity while maintaining accuracy with some extensions.

Contribution

It extends generalized seniority calculations to open-shell nuclei with realistic interactions, assessing its accuracy beyond semimagic nuclei.

Findings

Significant accuracy achieved with one broken pair approximation for Ti isotopes.

Cr isotopes require more broken pairs for qualitative accuracy.

The scheme reduces computational complexity while maintaining key observables.

Abstract

Generalized seniority provides a truncation scheme for the nuclear shell model, based on pairing correlations, which offers the possibility of dramatically reducing the dimensionality of the nuclear shell-model problem. Systematic comparisons against results obtained in the full shell-model space are required to assess the viability of this scheme. Here, we extend recent generalized seniority calculations for semimagic nuclei, the Ca isotopes, to open-shell nuclei, with both valence protons and valence neutrons. The even-mass Ti and Cr isotopes are treated in a full major shell and with realistic interactions, in the generalized seniority scheme with one broken proton pair and one broken neutron pair. Results for level energies, orbital occupations, and electromagnetic observables are compared with those obtained in the full shell-model space. We demonstrate that, even for the Ti isotopes, significant benefit would be obtained in going beyond the approximation of one broken pair of each type, while the Cr isotopes require further broken pairs to provide even qualitative accuracy.