The emergence of classical behaviour in the quantum fluctuations of a scalar field in an expanding universe

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Abstract
The author investigates the evolution of a massless, conformally coupled scalar field interacting with an environment in a spatially flat FRW metric. The environment is taken to be a second massless, conformally coupled scalar field. By finding the ground state wavefunctional of the coupled system and integrating out the unobservable scalar field the author obtains a reduced density matrix for the system, and then uses the reduced density matrix to show that classical behaviour emerges for wavelengths greater than the Hubble radius. This occurs despite the absence of particle creation.