Decoherence from isocurvature perturbations in inflation

Abstract

We discuss the possible role of isocurvature perturbations for the quantum decoherence ofthe curvature perturbation during inflation. We point out that if the inflaton trajectory infield space is curved, the adiabatic mode is generically coupled to the isocurvaturemode and thus tracing out the latter can cause the curvature perturbation todecohere. We explicitly investigate this suggestion in a model of inflation with twodecoupled massive fields and find that decoherence is effective for a wide range ofmass ratios. In particular, we calculate the entanglement entropy for this modeland show that it grows after horizon exit, providing a quantitative measure fordecoherence.