  In order to calculate the power spectrum generated during a stage of
inflation, we have to specify the quantum state of the inflaton perturbations,
which is conventionally assumed to be the Bunch-Davies vacuum. We argue that
this choice is justified only if the interactions of cosmological perturbations
are strong enough to drive excited states toward the vacuum. We quantify this
efficiency by calculating the decay probabilities of excited states to leading
order in the slow-roll expansion in canonical single-field inflationary models.
These probabilities are suppressed by a slow-roll parameter and the squared
Planck mass, and enhanced by ultraviolet and infrared cut-offs. For natural
choices of these scales decays are unlikely, and, hence, the choice of the
Bunch-Davies vacuum as the state of the primordial perturbations does not
appear to be warranted.
