Harrison-Z'eldovich primordial spectrum is consistent with observations

TL;DR

This paper examines whether the Harrison-Z'eldovich primordial spectrum aligns with current cosmological observations, suggesting it is only marginally disfavored when considering reionization models, with future Planck data expected to clarify this.

Contribution

It demonstrates that the Harrison-Z'eldovich spectrum remains compatible with observations under more general reionization scenarios.

Findings

HZ spectrum is marginally disfavored with simple models

Reionization scenario affects the compatibility

Future Planck data will clarify the spectrum's validity

Abstract

Inflation predicts primordial scalar perturbations with a nearly scale-invariant spectrum and a spectral index approximately unity (the Harrison--Zel'dovich (HZ) spectrum). The first important step for inflationary cosmology is to check the consistency of the HZ primordial spectrum with current observations. Recent analyses have claimed that a HZ primordial spectrum is excluded at more than 99% c.l.. Here we show that the HZ spectrum is only marginally disfavored if one considers a more general reionization scenario. Data from the Planck mission will settle the issue.