In the following section, by treating a simple example, we obtain an effective interaction between the original and tilde
spaces. It may be trivial that effective interactions appear owing to renormalization procedure. However, these effective
interactions enable us to understand a plausible treatment of a heat bath and they support the previous suggestions
[15,20–22] for the dissipative formulation of TFD. In Section 3, the present new perspective is applied to many-body systems.
Summary and discussions are included in Section 4.