标题： 格点上的瞬子和手征对称性 显示英文标题

标题： Instantons and Chiral Symmetry on the Lattice

摘要： 我探讨了在手征极限下， instanton（瞬子）在多大程度上再现了QCD（量子色动力学）。在重构平滑蒙特卡洛格点配置的瞬子内容后，我使用手征优化的clover费米子作用，将这一瞬子集合上的强子光谱与原始“物理”平滑配置上的光谱进行了比较。通过研究简单实例中的零模区域，我发现优化的作用给出了对此区域的一个令人满意的描述。通过Banks-Casher公式，瞬子本身被证明会破坏手征对称性，但在瞬子背景下的强子相关函数受到自由夸克传播的强烈影响。这导致了不自然轻的质量和矢量介子通道与赝标介子通道之间的小分裂。叠加一个零动量规范场涨落（torons）的微扰集合于瞬子之上，发现足以消除自由夸克并恢复物理的强子相关函数。我提出，在有限体积中存在的torons可能需要用来补偿由于瞬子集合中缺乏禁闭而引起的不自然大的有限大小效应。 显示英文摘要

摘要： I address the question of how much of QCD in the chiral limit is reproduced by instantons. After reconstructing the instanton content of smoothed Monte Carlo lattice configurations, I compare hadron spectroscopy on this instanton ensemble to the spectroscopy on the original ``physical'' smoothed configurations using a chirally optimised clover fermion action. By studying the zero mode zone in simple instances I find that the optimised action gives a satisfactory description of it. Through the Banks-Casher formula, instantons by themselves are shown to break chiral symmetry but hadron correlators on the instanton backgrounds are strongly influenced by free quark propagation. This results in unnaturally light hadrons and a small splitting between the vector and the pseudoscalar meson channels. Superimposing a perturbative ensemble of zero momentum gauge field fluctuations (torons) on the instantons is found to be enough to eliminate the free quarks and restore the physical hadron correlators. I argue that the torons that are present only in finite volumes, are probably needed to compensate the unnaturally large finite size effects due to the lack of confinement in the instanton ensemble.