Quasi-particle field in nonequilibrium quantum field theory

Esteban A. Calzetta, B. L. Hu

M. Guida

H. Matsumoto, S. Sakamoto

In recent experiments of Bose-Einstein condensation of a magnetically trapped dilute alkaline atomic gas, the nonequilibrium process of thermalization into the condensed state has been observed in a reasonably long time scale. This presents a new challenge to develop a theory to treat strongly space-time dependent nonequilibrium processes. In this paper, we present a nonequilibrium formulation of Bose-Einstein condensed states in the field theoretical framework of thermo-field dynamics. By use of an effective Hamiltonian method, a quasi-particle field equation is derived. This equation contains information regarding the renormalized energy, decay width and time-variation of particle distributions. It is shown that, in the present formulation, the strong space-time dependence can be treated, even including quantum corrections, as the use of the quasi-particle field equation enables us to factorize double-time functions of the self-energy.

Gert Aarts A

Ryan Heary, Jong E. Han

Burgess

Quasiparticle descriptions of nonequilibrium physics hold the promise of tracking the relevant degrees of freedom in calculations of statistical systems, as well as providing an important formal perspective on quantum field theories away from equilibrium.A formulation of nonequilibrium, quasiparticle field theory is presented here.The Schwinger closed time path generating functional and generalized sources are used to develop schematic field theories which can be adapted to real problems.The importance of the source method for effective nonequilibrium theories is argued and the physical interpretation of the formalism is discussed, including its possible applicability to biological dynamics.