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arXiv · nucl-th/9610045

Neutron-Proton Correlations in an Exactly Solvable Model

J. Engel·S. Pittel·P. Vogel·M. Stoitsov·J. Dukelsky
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Abstract

We examine isovector and isoscalar neutron-proton correlations in an exactly solvable model based on the algebra SO(8). We look particularly closely at Gamow-Teller strength and double beta decay, both to isolate the effects of the two kinds of pairing and to test two approximation schemes: the renormalized neutron-proton QRPA (RQRPA) and generalized BCS theory. When isoscalar pairing correlations become strong enough a phase transition occurs and the dependence of the Gamow-Teller beta+ strength on isospin changes in a dramatic and unfamiliar way, actually increasing as neutrons are added to an N=Z core. Renormalization eliminates the well-known instabilities that plague the QRPA as the phase transition is approached, but only by unnaturally suppressing the isoscalar correlations. Generalized BCS theory, on the other hand, reproduces the Gamow-Teller strength more accurately in the isoscalar phase than in the usual isovector phase, even though its predictions for energies are equally good everywhere. It also mixes T=0 and T=1 pairing, but only on the isoscalar side of the phase transition.

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J. Engel, S. Pittel, P. Vogel, M. Stoitsov, J. Dukelsky. 1996-10-29. Neutron-Proton Correlations in an Exactly Solvable Model. https://doi.org/10.1103/physrevc.55.1781

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