| We studied some methods in lattice QCD such as generating configurations, smoothing and calculating topological charge and density. These methods were employed to investigate several important problems and achieved benefited results. Topological charge susceptibility Xt for pure gauge SU(3) theory at finite temperature was studied using anisotropic lattices. The over-improved stout-link smoothing method was utilized to calculate the topological charge. Near the phase tran-sition point we found a rapid declining behavior for Xt as the temperature increased from zero temperature to 1.9Tc which indicates the existence of topological excitations far above Tc. The 4th order cumulant c4 of topological charge, as well as the ratio c4/χt were also investigated. Re-sults of c4 show step-like behavior near Tc while the ratio at high temperature agrees with the value as predicted by the diluted instanton gas model. We also studied the probing method to ex-tract the topological density by tracing Dov, and compared the results of topological density with that by point-source tracing. The derivation introduced by multi-point source was discussed, and confirmed the great advantage of saving computing resource especially for larger lattices with ac-ceptable accuracy. Due to similar locality of the traced operator, the probing method can be applied to solve some tough problems such as calculating the disconnected Feynman diagram. |
