Topological defects as inhomogeneous condensates in quantum field theory:: Kinks in (1+1) dimensional λψ4 theory

We study topological defects as inhomogeneous (localized) condensates of particles in quantum field theory. In the framework of the closed-time-path formalism. we consider explicitly a (1 + 1) dimensional gimelpsi(4) model and construct the Heisenberg picture field operator psi in the presence of kinks. We show how the classical kink solutions emerge from the vacuum expectation value of such an operator in the Born approximation and/or gimel-->0 limit. The presented method is general in the sense that it applies also to the case of finite temperature and to non-equilibrium it also allows for the determination of Green's functions in the presence of topological defects. We discuss the classical kink solutions at T not equal 0 in the high temperature limit. We conclude with some speculations on the possible relevance of our method for the description of the defect formation during symmetry-breaking phase transitions. (C) 2002 Elsevier Science (USA).