Self-consistent renormalisation in thermofield dynamics

From the consideration of quasiparticles in thermal situations, the authors derive a universal expression of the self-consistent renormalisation condition in thermofield dynamics. This condition is valid even when the renormalised energy becomes time dependent, and provides us with four independent self-consistent equations for four real parameters, i.e. renormalised energy, dissipative coefficient, number density and a new degree of freedom chi , which is a phase in thermal doublet space.