用格点量子色动力学研究无中子双β衰变的核矩阵元
Nuclear Matrix Elements for Neutrinoless Double Beta Decay from Lattice QCD
摘要：
虽然中微子振荡实验已经证明中微子具有小的非零质量，但关于它们的性质和衰变模式仍有很多未知数。一种潜在的衰变模式-无中微子双β衰变（$0 νββ$）-是实验研究的一个特别有趣的目标，因为它的观测将暗示中微子是一种马约拉纳粒子，证明轻子数守恒在自然界中是违反的，并对中微子质量和混合角给出进一步的限制。然而，将$0 νββ$衰变率的实验约束与中微子质量联系起来，需要以非微扰核矩阵元的形式进行理论输入，这仍然难以可靠地计算。在这次演讲中，我们将讨论进展的第一性原理计算的相关核矩阵元素使用格点量子色动力学和有效场论技术，假设由轻马约拉纳中微子介导的无中微子双β衰变。我们将显示初步结果的$π^{-} \rightarrow π^{+} e^{-} e^{-}$过渡振幅计算的$16^{3} \times 32$域壁费米子晶格的介子质量为420 MeV，并讨论改进的方法适用于一般的晶格计算的$0 νββ$衰变振幅。
英文摘要：
While neutrino oscillation experiments have demonstrated that neutrinos have small, nonzero masses, much remains unknown about their properties and decay modes. One potential decay mode --- neutrinoless double beta decay ($0 νββ$) --- is a particularly interesting target of experimental searches, since its observation would imply that the neutrino is a Majorana particle, demonstrate that lepton number conservation is violated in nature, and give further constraints on the neutrino masses and mixing angles. Relating experimental constraints on $0 νββ$ decay rates to the neutrino masses, however, requires theoretical input in the form of non-perturbative nuclear matrix elements which remain difficult to calculate reliably. In this talk we will discuss progress towards first-principles calculations of relevant nuclear matrix elements using lattice QCD and effective field theory techniques, assuming neutrinoless double beta decay mediated by a light Majorana neutrino. We will show preliminary results for the $π^{-} \rightarrow π^{+} e^{-} e^{-}$ transition amplitude computed on a $16^{3} \times 32$ domain wall fermion lattice with a pion mass of 420 MeV, and discuss improved methods applicable to general lattice calculations of $0 νββ$ decay amplitudes.
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