The coupling between the IAS and the IMS Original Research Article

In a previous paper we have studied the structure of the Isobaric Analogue State (IAS) using a realistic single-particle model within a formalism that allows to disentangle real effects of isospin violations from spurious effects associated with the construction of basis states. In this work we discuss the influence of the Isovector Monopole State (IMS) on the width of the IAS. According to our results, the presence of a collective IMS is necessary to preserve the empirically found isolation of the IAS from states of the background. This is valid for a simplified harmonic oscillator model and for a realistic single-particle basis as well, since for both cases there is a strong Coulomb mixing between the IAS and the IMS, which increases at the expense of decreasing the mixing between the IAS and the ΔN=0 configuration states. The prediction of the total width of the IAS remains in reasonable agreement with the experimental value in a calculation without free parameters.