Covariant energy density functionals with and without tensor couplings at the Hartree-Bogoliubov level

TL;DR

This paper investigates the effects of tensor terms in covariant energy density functionals at the Hartree-Bogoliubov level, demonstrating improvements in nuclear property predictions across the nuclear chart and in infinite nuclear matter.

Contribution

The study introduces new density-dependent functionals including tensor terms and evaluates their impact on nuclear structure and matter properties, showing enhanced predictive accuracy.

Findings

Improved RMS binding energies and spin-orbit splittings.

Better agreement of Dirac mass with experimental data.

Small modifications to potential energy surfaces and densities.

Abstract

Background: The study of additional terms in functionals is relevant to better describe nuclear structure phenomenology. Among these terms, the tensor one is known to impact nuclear structure properties, especially in neutron-rich nuclei. However, its effect has not been studied on the whole nuclear chart yet. Purpose: The impact of terms corresponding to the tensor at the Hartree level, is studied for infinite nuclear matter as well as deformed nuclei, by developing new density-dependent functionals including these terms. In particular, we study in details the improvement such a term can bring to the description of specific nuclear observables. Methods: The framework of covariant energy density functional is used at the Hartree-Bogoliubov level. The free parameters of covariant functionals are optimized by combining Markov-Chain-Monte-Carlo and simplex algorithms. Results: An improvement of the RMS binding energies, spin-orbit splittings and gaps is obtained over the nuclear chart, including axially deformed ones, when including tensors terms. Small modifications of the potential energy surface and densities are also found. In infinite matter, the Dirac mass is shifted to a larger value, in better agreement with experiments. Conclusions: Taking into account additional terms corresponding to the tensor terms in the vector-isoscalar channel at the Hartree level, improves the description of nuclear properties, both in nuclei and in nuclear matter.