Complex-mass scheme and effective field theory

量子色动力学是以夸克为物质成分，胶子为强力载体的强相互作用的基础场论。然而，渐近观测到的状态是强子，它们是颜色中性的，由夸克和胶子组成的复合物体。在低能量下，强子之间的强相互作用可以用有效场论(EFT)来描述，该理论使用强子场而不是夸克和胶子作为动力学自由度。相对应的介子EFT是介子手征微扰理论。给出一个一致的功率计算方案，EFT可以通过附加的场来扩展，例如产生重子手征微扰理论的核子。为了同时考虑激发态和不稳定态，我们提出了用复质量方案(CMS)来评价强子共振的物理特性。不稳定粒子的质量和宽度的手征极限作为输入参数。借助于适当选择的重整化条件，CMS允许对不稳定粒子的物理观测进行微扰处理。

Quantum chromodynamics is the fundamental field theory of the strong interactions with quarks as its matter constituents and gluons as the carriers of the strong force. However, the asymptotically observed states are hadrons which are color-neutral, composite objects made out of quarks and gluons. At low energies, the strong interactions among hadrons may be described in terms of an effective field theory (EFT) using hadron fields instead of quarks and gluons as dynamical degrees of freedom. The corresponding EFT in terms of pions is mesonic chiral perturbation theory. Given a consistent power counting scheme, the EFT may be extended by additional fields such as the nucleon resulting in baryon chiral perturbation theory. In order to take also excited, unstable states into account, we propose the application of the complex-mass scheme (CMS) to the evaluation of physical characteristics of hadron resonances. The chiral limit of the masses and widths of the unstable particles serve as input parameters. With the aid of suitably chosen renormalization conditions, the CMS allows for a perturbative treatment of physical observables of unstable particles.