摘要：When analyzing the particle-like excitations in quantum field theory it is natural to regard
the field mode corresponding to the particle momentum as an open quantum system, together
with the opposite momentum mode. Provided that the state of the field is stationary,
homogeneous, and isotropic, this scalar two-mode system can be equivalently represented in
terms of a pair of quantum Brownian oscillators under a Gaussian approximation. In other
words, the two-mode system behaves as if it were interacting linearly with some effective
environment. In this paper we build the details of the effective linear coupling and the
effective environment, and argue that this quantum Brownian representation provides a
simple, universal, and nonperturbative characterization of any single particle-like excitation.
As immediate applications of the equivalence, we reanalyze the interpretation of the self-energy
in terms of decay rates in a general background state and present the master equation
for the field mode corresponding to the particle momentum.
