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arXiv 1303.4553nucl-th
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用四重态处理类粒子配对

Treatment of like-particle pairing with quartets

M. Sambataro, N. Sandulescu

摘要:

用四体关联结构描述有限类费米子系统中一般配对哈密顿量诱导的基态关联。这些是两对处于时间反转状态的粒子的乘积的实叠加。四元组是通过在受限模型空间中对哈密顿量进行对角化的迭代序列变分确定的,并且原则上都是彼此不同的。基态被表示为四重态的乘积,根据粒子的数量(假设是偶数,在任何情况下),增加一个额外的集体对。额外的一对也是由变分决定的。在球对称平均场中配对的情况下,四重态和额外对(如果有的话)的特征都是总角动量J=0。四重态形式的实际应用进行了Sn同位素与价中子在50-82中子壳层。精确的基态相关能,占领数和对转移矩阵元素的再现到一个非常高的精度。形式主义也有助于自己的配对哈密顿量的最低资历0和2激发态的一个简单和准确的描述。最后讨论了一个简化的基态表示为相同的四重态的产物,并发现大大提高后,更传统的粒子数投影BCS方法。

英文摘要:

The ground state correlations induced by a general pairing Hamiltonian in a finite system of like fermions are described in terms of four-body correlated structures (quartets). These are real superpositions of products of two pairs of particles in time-reversed states. Quartets are determined variationally through an iterative sequence of diagonalizations of the Hamiltonian in restricted model spaces and are, in principle, all distinct from one another. The ground state is represented as a product of quartets to which, depending on the number of particles (supposed to be even, in any case), an extra collective pair is added. The extra pair is also determined variationally. In case of pairing in a spherically symmetric mean field, both the quartets and the extra pair (if any) are characterized by a total angular momentum J=0. Realistic applications of the quartet formalism are carried out for the Sn isotopes with the valence neutrons in the 50-82 neutron shell. Exact ground state correlation energies, occupation numbers and pair transfer matrix elements are reproduced to a very high degree of precision. The formalism also lends itself to a straightforward and accurate description of the lowest seniority 0 and 2 excited states of the pairing Hamiltonian. A simplified representation of the ground state as a product of identical quartets is eventually discussed and found to improve considerably upon the more traditional particle-number projected-BCS approach.

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