Plane waves in a general Robertson-Walker background

Abstract

We present an exact solution for the plane wave mode functions of a massless, minimally coupled scalar propagating in an arbitrary homogeneous, isotropic and spatially flat geometry. Our solution encompasses all previous solvable special cases such as de Sitter and power law expansion. Moreover, it can generate the mode functions for gravitons. We discuss some of the many applications that are now possible.

Comments: 11 pages, revtex4, no figures, version 3 is vastly expanded (from 57 eqns to 166) to give an explicit expression for the transfer matrix, and to expand it in the ultraviolet and the infrared. We use the infrared limit to give an improved result for the gravitational wave contribution to CMB anisotropies