Density perturbations, gravity waves and the cosmic microwave background

Abstract

We assess the contribution to the observed large scale anisotropy of the cosmic microwave background radiation, arising from both gravity waves as well as adiabatic density perturbations, generated by a common inflationary mechanism in the early Universe. We find that for inflationary models predicting power law primordial spectra |δ_k|²∝kⁿ, the relative contribution to the quadrupole anisotropy from gravity waves and scalar density perturbations, depends crucially upon n. For n< 0.84, gravity waves perturb the CMBR by a larger amount than density perturbations, whereas for n>0.84 the reverse is true. Normalizing the amplitude of the density perturbation spectrum at large scales, using the observed value of the COBE quadrupole, we determine (δM/M)16^-the rms density contrast on scales σ 16h^-1₅₀ Mpc, for cosmological models with cold dark matter. We find that for n< 0.75, a large amount of biasing is required in order to reconcile theory with observations. We also determine the value of the inflationary Hubble parameter and the COBE-normalized amplitude and spectrum of gravity waves from inflation.