Like particles vs proton-neutron pairs: Phase transitions in realistic model spaces

Abstract

The quasiparticle random phase approximation (QRPA) and its renormalized version (RQRPA) are used to investigate the particle number fluctuations and the number of particle pairs with J=0, T=1 and J=1: T = 0 in the ground state of Ge-76 as a function of the residual proton-neutron interaction. The study is performed

in realistic model spaces including many single particle orbitals. While the RQRPA remains stable after the QRPA collapse the sudden increase in particle number fluctuations exhibits its limitations. The analysis of the number of pairs shows that the isoscalar-isovector phase transition found in exact calculations is causing the QRPA collapse and is missed in the RQRPA formalism. [S0556-2813(98)03710-8].