Abstract
We study adiabatic ~curvature! and entropy ~isocurvature! perturbations produced during a period of cosmological
inflation that is driven by multiple scalar fields with an arbitrary interaction potential. A local
rotation in field space is performed to separate out the adiabatic and entropy modes. The resulting field
equations show explicitly how on large scales entropy perturbations can source adiabatic perturbations if the
background solution follows a curved trajectory in field space, and how adiabatic perturbations cannot source
entropy perturbations in the long-wavelength limit. It is the effective mass of the entropy field that determines
the amplitude of entropy perturbations during inflation. We present two applications of the equations. First, we
show why one in general expects the adiabatic and entropy perturbations to be correlated at the end of inflation,
and calculate the cross correlation in the context of a double inflation model with two non-interacting fields.
Second, we consider two-field preheating after inflation, examining conditions under which entropy perturbations
can alter the large-scale curvature perturbation and showing how our new formalism has advantages in
numerical stability when the background solution follows a non-trivial trajectory in field space.
Original language | English |
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Article number | 023506 |
Pages (from-to) | 023506 |
Journal | Physical Review D |
Volume | 63 |
Issue number | 2 |
Early online date | 27 Dec 2000 |
DOIs | |
Publication status | Published - 15 Jan 2001 |