Role of three-nucleon forces and many-body processes in nuclear pairing

TL;DR

This paper investigates how three-nucleon forces and many-body processes influence nuclear pairing gaps in calcium isotopes, showing that including these effects improves agreement with experimental data and enhances understanding of nuclear structure evolution.

Contribution

It provides a comprehensive microscopic analysis of pairing in calcium isotopes, emphasizing the significant impact of three-nucleon forces and many-body correlations on pairing gaps.

Findings

Inclusion of 3N forces reduces pairing strength compared to two-nucleon interactions.

Particle-hole contributions and 3N forces improve agreement with experimental pairing gaps.

Predictions for 2+ excitation energies in 54Ca are provided.

Abstract

We present microscopic valence-shell calculations of pairing gaps in the calcium isotopes, focusing on the role of three-nucleon (3N) forces and many-body processes. In most cases, we find a reduction in pairing strength when the leading chiral 3N forces are included, compared to results with low-momentum two-nucleon (NN) interactions only. This is in agreement with a recent energy density functional study. At the NN level, calculations that include particle-particle and hole-hole ladder contributions lead to smaller pairing gaps compared with experiment. When particle-hole contributions as well as the normal-ordered one- and two-body parts of 3N forces are consistently included to third order, we find reasonable agreement with experimental three-point mass differences. This highlights the important role of 3N forces and many-body processes for pairing in nuclei. Finally, we relate pairing gaps to the evolution of nuclear structure in neutron-rich calcium isotopes and study the predictions for the 2+ excitation energies, in particular for 54Ca.