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Neutron-proton correlations in an exactly solvable model

Engel, J. and Pittel, S. and Stoitsov, M. and Vogel, P. and Dukelsky, J. (1997) Neutron-proton correlations in an exactly solvable model. Physical Review C, 55 (4). pp. 1781-1788. ISSN 0556-2813. doi:10.1103/PhysRevC.55.1781.

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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 β decay, both to isolate the effects of the two kinds of pairing and to test two approximation schemes: the renormalized neutron-proton quasiparticle random phase approximation (QRPA) and generalized BCS theory. When isoscalar pairing correlations become strong enough a phase transition occurs and the dependence of the Gamow-Teller β+ 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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Vogel, P.0000-0003-0587-5466
Additional Information:©1997 The American Physical Society Received 29 October 1996 This work was supported in part by the National Science Foundation under Grant Nos. PHY-9303041, PHY-9600445, and INT-9224875, by the U.S. Department of Energy under Grant Nos. DE-FG05-94ER40827 and DE-FG03-88ER-40397, by NATO under Grant No. CRG.900466, by the Bulgarian National Foundation for Scientific Research under Contract No. F-527, by the DIGICYT (Spain) under Contract No. PB95/0123, and by the European Union under Contract No. CI1*-CT94-0072. One of the authors (M.V.S.) would like to acknowledge the support of the Fulbright Foundation, and two others (J.E. and P.V.) the hospitality of the Institute for Nuclear Theory at the University of Washington, where some of this work was carried out.
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Deposited On:16 Apr 2006
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