Neutron-proton pairing in the BCS approach

Abstract

We investigate the BCS treatment of neutron-proton pairing involving time-reversed orbits. We conclude that an isospin-symmetric Hamiltonian, treated with the help of the generalized Bogolyubov transformation, fails to describe the ground state pairing properties correctly. In order for the np isovector pairs to coexist with the like-particle pairs, one has to break the isospin symmetry of the Hamiltonian by artificially increasing the strength of the np pairing interaction above its isospin-symmetric value. We briefly discuss the prescription how to choose the coupling constant of this auxiliary isospin-breaking pairing force. ͓S0556-2813͑97͒03710-2͔ PACS number͑s͒: 21.60. Fw, 21.30.Fe, 23.40.Hc

Dynamical symmetry of isobaric analog0+states in medium mass nuclei

“…Even though the states are represented as J = 0 pairs, the interaction that governs them is not exclusively pairing in the J = 0 channel, but must also include the important pn J odd ≥ 1 isoscalar (T = 0) interaction. The significant interplay between these isovector and isoscalar interactions is evident in the low-lying structure of N = Z odd-odd nuclei and has been the focus of a large number of experimental [15,16,17,18] and theoretical studies [6,19,20,21,22,23,24,25,26,27,28].…”

Isovector pairing in odd-A proton-rich nuclei

“…(For the formalism, applicable to seniority-zero states, see Ref. [7,8].) Although the matrices one must diagonalize are no longer tiny, they are still small.…”

Effects of the particle-number projection on the isovector pairing energy

“…Renewed interest in the study of the neutron-proton (np) pairing correlations occurred recently (cf., e.g., [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]) due to the development of the radioactive beam facilities that made possible the experimental study of medium mass nuclei such as N Z. The study of these proton-rich nuclei is not only interesting from the nuclear structure point of view, but it is also important in the astrophysical context.…”

“…Most often, pairing is treated within a generalized BCS treatment [1,2,3,4,5,6,7,8]. However, the shortcomings of this approach are well known: the most important of them is the number symmetry breaking that may imply serious errors in the evaluation of several physical observables.…”