  Relativistic quantum field theories for complex scalar and Dirac fields are
investigated in non-equilibrium thermo field dynamics. The thermal vacuum is
defined by the Bogoliubov transformed creation and annihilation operators. Two
independent Bogoliubov parameters are introduced for a charged field. Its
difference naturally induces the chemical potential. Time-dependent thermal
Bogoliubov transformation generates the thermal counter terms. We fix the terms
by the self-consistency renormalization condition. Evaluating the thermal
self-energy under the self-consistency renormalization condition, we derive the
quantum Boltzmann equations for the relativistic fields.
