Research On Disconnected Quark Loops And Topological Structure Of Vacuum In Lattice QCD

We had calculated the quark disconnected loops,especially the scalar and pseu-doscalar quark loops.Calculation of disconnected quark loops in lattice QCD is very time consuming.Stochastic noise methods are generally used to estimate these loops.However,stochastic estimation gives large errors in the calculations of disconnected diagrams.We use the symmetric multi-probing source(SMP)method to estimate the disconnected quark loops,and compare the results with the Z(2)noise method and the spin-color explicit(SCE)method with lattice volume 123 x 24 and lattice spacing a ≈0.1fm.The results show that the SMP method is very suitable for the calculation of pseudoscalar disconnected quark loops.However,the SMP and SCE methods do not have an obvious advantage over the noise method in the evaluation of the scalar disconnected loops.In addition,we had studied the topological properties of QCD vacuum.We ana-lyze the dependence of the topological charge density from the overlap operator on the Wilson mass parameter in the overlap kernel by the symmetric multi-probing source(SMP)method.We observe that the non-trivial topological objects are removed as the Wilson mass is increased.A comparison of topological charge density calculated by the SMP method using fermionic definition with that of bosonic definition by the Wilson flow method is shown.A matching procedure for these two methods is used.We find that there is a best match for topological charge density between gluonic definition and fermionic definition with different Wilson mass.By using these matching procedures,the proper Wilson flow time τ in the calculation of topological charge density can be estimated.As the lattice spacing a decreases,the proper radius of Wilson flow(?)also decreases.We also show topological charge density on pre-flowed configurations and find that more Wilson flow time is required to reproduce the topological charge density q(x)for UV-filtered configurations which are smoothed using the Wilson flow method.We attempt to use the proper Wilson flow time τ obtained by the matching procedures in the calculation of the topological charge density correlator(TCDC),and extract the pseudoscalar glueball mass from the TCDC based on bosonic definition.