STABLE QUASI-PARTICLE PICTURE IN THERMAL QUANTUM-FIELD PHYSICS

It is well known that physical particles are thermally dissipative at finite temperature. In this paper we reformulate both the equilibrium and nonequilibrium thermal field theories in terms of stable quasipart icles. We will redefine the thermal doublets, the double tilde conjuga tion rules and the thermal Bogoliubov transformations so that our theo ry can be consistent for most general situations. All operators, inclu ding the dissipative physical particle operators, are realized in a Fo ck space defined by the stable quasiparticles. The propagators of the physical particles are expressed in terms of the operators of such sta ble quasiparticles, which is a simple diagonal matrix wi th the diagon al elements being the temporal step functions, same as the propagators in the usual quantum field theory without thermal degrees of freedom. The proper self-energies are also expressed in terms of these stable quasiparticle propagators. This formalism inherits the definition of o n-shell self-energy in the usual quantum field theory. With this defin ition, a self-consistent renormalization is formulated which leads to quantum Boltzmann equation and the entropy law. With the aid of a doub let vector algebra we have an extremely simple recipe for computing Fe ynman diagrams. We apply this recipe to several examples of equilibriu m and nonequilibrium two-point functions, and to the kinetic equation for the particle numbers.