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arXiv 1710.06352nucl-thastro-ph.SR
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同位旋禁戒电偶极俘获与$α(d,γ)^6$ Li反应

Isospin-forbidden electric-dipole capture and the $α(d,γ)^6$Li reaction

Daniel Baye, E. M. Tursunov

摘要:

在长波长近似下,$E1$跃迁在同位旋零态之间是被禁止的。因此,在涉及$N = Z$核的反应中,$E1$辐射俘获受到强烈阻碍,但$E1$天体物理学$S$因子可能仍然与$E2$因子相当或大于该因子。在$α(d,γ)^6$ Li反应的背景下,在微观和三体方法中分析了对$E1$捕获的Isoscope和isovector贡献的理论表达。最低的非零项的运营商的推导和主导的贡献矩阵元素进行了讨论。在三体$α+n+p$模型中用这些贡献计算的天体物理$S$因子与最近的月球合作低能实验数据一致。这证实了正确处理的isovector $E1$过渡涉及小的同位旋一掺合物的波函数应该能够提供一个解释的数据没有可调的参数。精确质量处方通常用于避免潜在模型中$E1$基质元素的消失,但在微观水平上并不成立,因此不应用于此类反应。从初始$S$散射波捕获组件的重要性进行了讨论。

英文摘要:

At the long-wavelength approximation, $E1$ transitions are forbidden between isospin-zero states. Hence $E1$ radiative capture is strongly hindered in reactions involving $N = Z$ nuclei but the $E1$ astrophysical $S$ factor may remain comparable to, or larger than, the $E2$ one. Theoretical expressions of the isoscalar and isovector contributions to $E1$ capture are analyzed in microscopic and three-body approaches in the context of the $α(d,γ)^6$Li reaction. The lowest non-vanishing terms of the operators are derived and the dominant contributions to matrix elements are discussed. The astrophysical $S$ factor computed with some of these contributions in a three-body $α+n+p$ model is in agreement with the recent low-energy experimental data of the LUNA collaboration. This confirms that a correct treatment of the isovector $E1$ transitions involving small isospin-one admixtures in the wave functions should be able to provide an explanation of the data without adjustable parameter. The exact-masses prescription which is often used to avoid the disappearance of the $E1$ matrix element in potential models is not founded at the microscopic level and should not be used for such reactions. The importance of capture components from an initial $S$ scattering wave is also discussed.

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