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arXiv 1509.08078nucl-thnucl-ex
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核的一阶和二阶耦合无规相近似模激发

Nuclear excitations as coupled one and two random--phase--approximation modes

D. Gambacurta, F. Catara, M. Grasso, M. Sambataro, M. V. Andrés, E. G. Lanza

摘要:

我们提出了一种推广的随机相位近似(RPA),其中RPA声子被用作构建块来构建激发态。在我们的模型中,我们称之为双RPA(DRPA),我们包括多达两个RPA声子。这是一种近似和简化的方法,相对于完全第二随机相位近似(SRPA),通过包括两个粒子-两个空穴配置来扩展RPA。DRPA中没有遇到与违反稳定性条件有关的标准SRPA模型的一些限制。我们还验证了在这项工作中,能量加权和规则是满意的。将该方法应用于$^{16}$ O核的低能模和巨共振。我们表明,该模型(i)产生一个全球性的能量向下移动相对于RPA光谱;(ii)提供了一个移动,但强烈减少相比,由标准SRPA产生的。该模型代表了一种替代的方式来纠正SRPA的异常能量转移,相比最近开发的扩展的SRPA,其中应用的减法程序。的DRPA提供的结果与实验的能量,除了那些低-躺态,有一个占主导地位的两个粒子-两个空穴的性质,在良好的协议。为了描述这种状态,需要更高阶的计算。

英文摘要:

We present an extension of the random--phase approximation (RPA) where the RPA phonons are used as building blocks to construct the excited states. In our model, that we call double RPA (DRPA), we include up to two RPA phonons. This is an approximate and simplified way, with respect to the full second random--phase approximation (SRPA), to extend the RPA by including two particle--two hole configurations. Some limitations of the standard SRPA model, related to the violation of the stability condition, are not encountered in the DRPA. We also verify in this work that the energy--weighted sum rules are satisfied. The DRPA is applied to low--energy modes and giant resonances in the nucleus $^{16}$O. We show that the model (i) produces a global downwards shift of the energies with respect to the RPA spectra; (ii) provides a shift that is however strongly reduced compared to that generated by the standard SRPA. This model represents an alternative way of correcting for the SRPA anomalous energy shift, compared to a recently developed extension of the SRPA, where a subtraction procedure is applied. The DRPA provides results in good agreeement with the experimental energies, with the exception of those low--lying states that have a dominant two particle--two hole nature. For describing such states, higher--order calculations are needed.

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