论文标题
大爆炸核合成的核反应的理论计算
Theoretical calculation of nuclear reactions of interest for Big Bang Nucleosynthesis
论文作者
论文摘要
标准的大爆炸核合成（BBN）预测了早期宇宙中光元素的丰度。即使与实验数据的总体协议很好，但仍然存在一些差异，这是$ {}^7 $ li和$ {}^6 $ li的遗物丰度。为了排除或确认这些情况，BBN模型需要精确的输入参数，特别是BBN核反应网络的横截面。但是，由于库仑屏障而导致的横截面的抑制使测量非常困难，并且受到大型系统错误的影响。因此，可靠的理论计算会导致基础，以减少不确定性。在这项工作中，我们介绍了两种核反应的理论研究，这些核反应与$ {}^6 $ li丰富相关，最近$α$+d $ \ rightarrow $ $ $ {}^6 $ li+$γ$和p+$ {}^6 $ li $ $ \ \ \ \ rightarrow $ $ $ $ $ $ $ $ $ $ $ upiatiat $ guatiat $ guatiate capture。对于第一个反应，我们使用所谓的AB-Initio方法，在该方法中，我们通过使用逼真的核电位来描述核子相互作用来解决完整的六体问题。特别是，我们集中于反应的最终状态的计算和表征，$ {}^6 $ li基态，重点是电磁静态结构以及从天体物理学角度（例如渐近归一化系数）相关的数量。为此，我们使用PISA组开发的超球形谐波方法，该方法首次提供了超过A = 4核系统的方法。相反，通过使用两体群集方法来研究第二个反应，其中质子和$ {}^6 $ li被视为无结构的颗粒。 LUNA协作使用了在这项工作中获得的发射光子的角度分布，以确定用于测量反应的检测器的效率。
Standard Big Bang Nucleosynthesis (BBN) predicts the abundances of the light elements in the early universe. Even if the overall agreement with the experimental data is good, still some discrepancies exist on the relic abundances of ${}^7$Li and ${}^6$Li. In order to exclude or confirm these scenarios, the BBN model needs precise input parameters, in particular the cross-sections of the BBN nuclear reaction network. However, the suppression of the cross-sections due to the Coulomb barrier makes the measurement very difficult and so affected by large systematic errors. Therefore, reliable theoretical calculations result fundamental in order to reduce the uncertainties. In this work we present a theoretical study of two nuclear reactions connected to ${}^6$Li abundance and recently the $α$+d$\rightarrow$ ${}^6$Li + $γ$ and the p+${}^6$Li$\rightarrow$${}^7$Be+$γ$ radiative captures. For the first reaction we use a so-called ab-initio approach in which we solve the full six-body problem by using realistic nuclear potentials to describe the nucleon interactions. In particular we concentrate on the calculation and characterization of the final state of the reaction, the ${}^6$Li ground state, focusing on the electromagnetic static structure and the quantities relevant from the astrophysical point of view such as the asymptotic normalization coefficient. For doing this we use the Hyperspherical Harmonic approach developed by the Pisa group providing for the first time the possibility of using this approach beyond A = 4 nuclear systems. The second reaction is instead studied by using a two-body cluster approach where the proton and ${}^6$Li are considered as structureless particles. The angular distribution of the emitted photon obtained in this work were used by the LUNA Collaboration to determine the efficiency of the detector used in the measurement of the reaction.
