Microscopic optical potentials for calcium isotopes

TL;DR

This paper develops microscopic optical potentials for calcium isotopes using advanced many-body methods, comparing different chiral interactions, and analyzing their effectiveness in reproducing neutron scattering data.

Contribution

It combines Green's function and coupled-cluster methods to construct optical potentials for calcium isotopes, highlighting the impact of many-body correlations and interaction choices.

Findings

Reproduces neutron scattering cross sections with both interactions.

Imaginary part of the potential is negligible, indicating missing correlations.

Adjusting the Green's function parameter improves results.

Abstract

We construct nucleonic microscopic optical potentials by combining the Green's function approach with the coupled-cluster method for $\rm{^{40}Ca}$ and $\rm{^{48}Ca}$. For the computation of the ground-state of $\rm{^{40}Ca}$ and $\rm{^{48}Ca}$, we use the coupled-cluster method in the singles-and-doubles approximation, while for the A = $\pm 1$ nuclei we use particle-attached/removed equation-of-motion method truncated at two-particle-one-hole and one-particle-two-hole excitations, respectively. Our calculations are based on the chiral nucleon-nucleon and three-nucleon interaction $\rm{NNLO_{sat}}$, which reproduces the charge radii of $^{40}$Ca and $^{48}$Ca, and the chiral nucleon-nucleon interaction $\rm{NNLO_{opt}}$. In all cases considered here, we observe that the overall form of the neutron scattering cross section is reproduced for both interactions, but the imaginary part of the potential, which reflects the loss of flux in the elastic channel, is negligible. The latter points to neglected many-body correlations that would appear beyond the coupled-cluster truncation level considered in this work. We show that, by artificially increasing the parameter $\eta$ in the Green's function, practical results can be further improved.