$np \to d γ$辐射俘获过程的从头计算
Ab initio calculation of the $np \to d γ$ radiative capture process
摘要：
本文用格点QCD方法计算了双核子系统的辐射俘获过程$np \to dγ$和光致衰变过程$γ^{(\ast)} d \to np$的短程两体电磁贡献。在核势模型中，这种贡献是由唯象的介子交换流描述的，而在本工作中，它们直接由QCD的夸克和胶子相互作用确定。在多个背景磁场中的中子-质子能级的计算进行了两个值的夸克质量，对应的π介子质量的$m_π\sim 450$和806 MeV，并结合无π介子核有效场论，以确定这些低能量的非弹性过程。外推到物理π介子质量，在入射中子速度为$v=2,200\ m/s$时得到了$σ^{lqcd}(np\to dγ)=332.4({\tiny \begin{array}{l}+5.4 \\ - 4.7\end{array}})\ mb$的截面，与$σ^{expt}(np \to dγ) = 334.2(0.5)\ mb$的实验值一致。
英文摘要：
Lattice QCD calculations of two-nucleon systems are used to isolate the short-distance two-body electromagnetic contributions to the radiative capture process $np \to dγ$, and the photo-disintegration processes $γ^{(\ast)} d \to np$. In nuclear potential models, such contributions are described by phenomenological meson-exchange currents, while in the present work, they are determined directly from the quark and gluon interactions of QCD. Calculations of neutron-proton energy levels in multiple background magnetic fields are performed at two values of the quark masses, corresponding to pion masses of $m_π\sim 450$ and 806 MeV, and are combined with pionless nuclear effective field theory to determine these low-energy inelastic processes. Extrapolating to the physical pion mass, a cross section of $σ^{lqcd}(np\to dγ)=332.4({\tiny \begin{array}{l}+5.4 \\ - 4.7\end{array}})\ mb$ is obtained at an incident neutron speed of $v=2,200\ m/s$, consistent with the experimental value of $σ^{expt}(np \to dγ) = 334.2(0.5)\ mb$.
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