The isoscalar monopole resonance of the alpha particle: a prism to nuclear Hamiltonians

TL;DR

This paper investigates the isoscalar monopole excitations of helium-4 using various nuclear interactions, revealing potential model dependencies and discrepancies with experimental data, thus providing insights into nuclear force models.

Contribution

It offers an ab-initio analysis of helium-4 monopole excitations with different realistic potentials, highlighting the potential model dependence of transition form factors.

Findings

Transition form factor F_M varies significantly with nuclear potential models.

Theoretical form factors differ from experimental data, especially for effective field theory potentials.

Discrepancies suggest unresolved issues in current nuclear force models.

Abstract

We present an ab-initio study of the isoscalar monopole excitations of 4He using different realistic nuclear interactions, including modern effective field theory potentials. In particular we concentrate on the transition form factor $F_{\cal M}$ to the narrow $0^+$ resonance close to threshold. F_M exhibits a strong potential model dependence, and can serve as a kind of prism to distinguish among different nuclear force models. Comparing to the measurements obtained from inelastic electron scattering off 4He, one finds that the state-of-the-art theoretical transition form factors are at variance with experimental data, especially in the case of effective field theory potentials. We discuss some possible reasons for such discrepancy, which still remains a puzzle.