As shown in Eq. (15), there appears an effective interaction between S0 and S˜
0 as γ tS0S˜
0. This interaction depends on the
parameter ϵ and J. Consequently, this kind of effective interaction does appear only in the dissipative system with a heat
bath. Once thermal noises are reduced, the effective TFD Hamiltonian Hˆ
eff does not include any thermal noise explicitly.
Then we can conclude that dissipative effects are renormalized into the effective interactions between the original and tilde
spaces. These contexts become much clear to consider the time differentials. Using the notations