Test of many-body methods on an exactly soluble model with backbending and gapless superconductivity

Abstract
The exactly soluble R(8) model of Krumlinde and Szymański is used as a testing ground for three many-body methods applied to the yrast band: (i) the self-consistent cranking model, (ii) self-consistent cranking plus random-phase approximation, and (iii) variation after projection of particle number. All three methods agree very well with exact results outside of the critical region. The behavior in the critical region is examined in detail.