Thermal quantum electrodynamics of nonrelativistic charged fluids.

The theory relevant to the study of matter in equilibrium with the radiation field is thermal quantum electrodynamics (TQED). We present a formulation of the theory, suitable for nonrelativistic fluids, based on a joint functional integral representation of matter and field variables. In this formalism cluster expansion techniques of classical statistical mechanics become operative.

Equilibrium correlations in charged fluids coupled to the radiation field.

We provide an exact microscopic statistical treatment of particle and field correlations in a system of quantum charges in equilibrium with a classical radiation field. Using the Feynman-Kac-Itô representation of the Gibbs weight, the system of particles is mapped onto a collection of random charged wires. The field degrees of freedom can be integrated out, providing an effective pairwise magnetic potential.

Bose gas beyond mean field.

We study a homogeneous Bose gas with purely repulsive forces. Using the Kac scaling of the binary potential we derive analytically the form of the thermodynamic functions of the gas for small but finite values of the scaling parameter in the low density regime. In this way we determine dominant corrections to the mean-field theory.

Self-consistent equation for an interacting Bose gas.

We consider interacting Bose gas in thermal equilibrium assuming a positive and bounded pair potential V(r) such that 0< integral dr V(r)=a< infinity. Expressing the partition function by the Feynman-Kac functional integral yields a classicallike polymer representation of the quantum gas. With the Mayer graph summation techniques, we demonstrate the existence of a self-consistent relation rho(mu)=F(mu-(a)rho(mu)) between the density rho and the chemical potential mu, valid in the range of convergence of Mayer series.