Decoherence properties of scalar field perturbations

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Abstract
The authors investigate the decoherence properties of two models of scalar field perturbations due to interaction with the environment. Their models are based on one scalar field that represents the inflaton field and others that are taken to be the environment, that is unobservable fields. They see that in a highly symmetric model, where they treat the environment as internal (angular) degrees of freedom, decoherence is not observed. If they break the symmetry, they do get some weak form of decoherence, furthermore, the decoherence properties are independent of the wavelength of the fields and thus, are not very helpful to the study of cosmological perturbations. The second model they study does not conserve the internal symmetry. They construct a two-scalar-field model with mass mixing. They integrate over the second scalar field and get an exponential decrease of the correlation length with time. Moreover, the speed of the decrease of the off-diagonal elements of the density matrix was faster for long wavelengths.