Quartet correlations in N = Z nuclei induced by realistic two-body interactions

Abstract

Two variational quartet models previously employed in a treatment of pairing forces are extended to the case of a general two-body interaction. One model approximates the nuclear states as a condensate of identical quartets with angular momentum J = 0 and isospin T = 0 while the other let these quartets to be all different from each other. With these models we investigate the role of alpha-like quartet correlations both in the ground state and in the lowest J = 0, T = 0 excited states of even-even N = Z nuclei in the sd-shell. We show that the ground state correlations of these nuclei can be described to a good extent in terms of a condensate of alpha-like quartets. This turns out to be especially the case for the nucleus 32 S for which the overlap between this condensate and the shell model wave function is found close to one. In the same nucleus, a similar overlap is found also in the case of the first excited 0 + state. No clear correspondence is observed instead between the second excited states of the quartet models and the shell model eigenstates in all the cases examined.

Band-like structures and quartets in deformed N=Z nuclei

“…In all cases α g,J=0 turns out to be the largest amplitude. This is especially the case for 28 Si, which clearly stands out for a much more prominent role of this amplitude as compared with the J > 0 ones. We shall further comment on this point below.…”

“…For what concerns 28 Si, what is most striking in the spectrum of Fig. 2(B) is the absence of a state 0 2 close to the state 4 1 as observed in both the shell model and the experimental spectrum.…”

“…In the latter case the quartets are also characterized by an angular momentum J = 0 [24]. The QCM formalism has been later on extended to a more general form of pn pairing which also included an isoscalar component [25][26][27] as well as to quite general Hamiltonians [28]. The link between the QCM condensate and the exact ground state has been recently analyzed in the case of the isovector pairing [29].…”

Pairing correlations and eigenvalues of two-body density matrix in atomic nuclei

“…In particular, as shown recently, the isovector plus isoscalar Hamiltonian (30) can be treated accurately in terms of alpha-like quartets built by two protons and two neutrons coupled to total isospin T = 0, rather than in terms of Cooper pairs [35]. It has also been shown that T = 0 alpha-like quartets are the main building blocks for systems governed by the general shell model Hamiltonian (33) [36][37][38]. These studies clearly show that 4-body correlations play a key role in the N=Z nuclei.…”

Collective treatment of the isovector pair correlations: Boson representation

“…One of the questions under investigations is an existence of α-type condensate in the ground states of nuclei [9,10,11,12,13,14,15]. The Quartet Condensate Model was proposed for studing of the isovector pairing and quarteting correlations in N=Z nuclei [16,17,18,19,20,21,22,23]. The boson approximation technique has been applied to description of the pairing and quarteting correlations [24].…”