- th / 9 61 00 45 v 1 2 9 O ct 1 99 6 Neutron - Proton Correlations in an Exactly Solvable Model
نویسندگان
چکیده
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 renor-malized 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 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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