Effective field theory for nucleons and light nuclei

我们计划用核子、π介子和光子的场论来研究单核子和轻核的性质。“有效”理论尊重强相互作用的基础理论的对称性：量子色动力学（QCD）。我们计划改进这些理论对核子性质的描述，并利用它们以一种与模型无关的方式确定核子间的作用力。所得结果将用于光子与少核子系统相互作用的计算。特别令人感兴趣的是康普顿散射，它为核子的内部结构提供了非常灵敏的探针，因为它可以用来确定描述核子对电磁场的响应的全套极化率。在中子的情况下，我们的工作将有助于从轻核实验中提取这些极化率。这些理论允许我们将核子的性质写成π质量的幂级数，π质量是衡量夸克质量破缺QCD手征对称性的强度。目前在大时空格点上的QCD模拟是使用比真实的世界大得多的夸克质量进行的。为了将这些计算结果外推到实际的夸克质量上，需要我们对核子性质的展开。

We plan to study the properties of single nucleons and light nuclei using field theories of nucleons, pions and photons. The 'effective' theories respect the symmetries of the underlying theory of the strong interaction: quantum chromodynamics (QCD). We plan to improve the description of nucleon properties in these theories, and to use them to determine the forces between nucleons in a model-independent way. The results will be applied to the calculations of the interactions of photons with few-nucleon systems. Of particular interest is Compton scattering which provides a very sensitive probe of the internal structure of the nucleon since it can be used to determine the complete set of polarisabilities which describe the repsonse fo a nucleon to an electromagnetic field. In the case of the neutron, our work will help with extracting these polarisabilities from experiments on light nuclei. These theories allow us to write nucleon properties as power series in the mass of the pion, which is a measure of how strongly the chiral symmetry of QCD is broken by the quark masses. Current simulations of QCD on large space-time lattices are carried out using quark masses that are much larger than those in the real world. Our expansions of nucleon properties will be needed to extrapolate the results of these calculations to realistic quark masses.