Clarifying transfer function approximations for the large-scale gravitational wave background in ΛCDM

In this paper we explore the solutions of gravitational wave transfer functions in the primordial universe. In doing so we clarify some misconceptions in the literature, show the ranges of validity of various analytic approximations and explore new aspects of the numerical solutions, such as the universal expansion due to dark energy. We also provide a new, simple analytic approximation for the transfer function that is accurate to within ~5% for all frequencies and redshifts of interest.

Arxiv preprint

Published version

Examples of three gravitational waves of different frequencies, with and without damping by neutrinos.