Effects of ground-state correlations on magnetic dipole excitations in $^{40}$Ca

TL;DR

This paper investigates how ground-state correlations influence magnetic dipole excitations in calcium-40 using an advanced theoretical framework, revealing that certain excitations significantly enhance magnetic transition strengths.

Contribution

It introduces an extended RPA approach derived from time-dependent density-matrix theory to accurately account for ground-state correlations in nuclear excitations.

Findings

Ground-state correlations significantly affect magnetic dipole transition strengths.

ERPA predicts strong magnetic dipole transitions due to two particle-two hole excitations.

Comparison shows ERPA's effectiveness over other extended RPA methods.

Abstract

The effects of ground-state correlations on the magnetic dipole excitations in $^{40}$Ca are studied using an extended random phase approximation (ERPA) derived from the time-dependent density-matrix theory. Comparison is made with other extended RPA approaches, the renormalized RPA, the self-consistent RPA and the extended second RPA which also include the effects of ground-state correlations. It is pointed out that direct excitations from two particle - two hole space which are properly treated in ERPA cause strong magnetic dipole transitions in $^{40}$Ca.