Gluons in the lattice SU(2) classical field
  The SU(2) gluonic correlation functions, glueball effective masses in the $J^{P}=0^{+}$, $2^{+}$ and $0^{-}$ channels were calculated from the lattice classical gauge configurations which were obtained by smoothing the thermal gauge configurations through the improved cooling method. The instanton-induced attractive force in the $0^{+}$ channel and the repulsive force in the $0^-$ channel are confirmed in the Monte Carlo simulation. There is evidence that the instanton vacuum contribution to the $0^+$ glueball mass is significant. 
Ying Chen, Ji-Min Wu and Bing He