We study primordial power spectra with a large-scale power deficit and their effect on the standard $\mathrm{\Lambda }\mathrm{CDM}$ cosmology. The standard power-law spectrum is subject to long-wavelength modifications described by some new parameters, resulting in corrections to the anisotropies in the cosmic microwave background. The new parameters are fitted to different datasets: Planck 2015 data for temperature and for both temperature and polarization, the low-redshift determination of $H_0$, and distances derived from baryonic acoustic oscillations. We discuss the statistical significance of the modified spectra, from both frequentist and Bayesian perspectives. Our analysis suggests motivations for considering models that break scalar-tensor consistency, or models with negligible power in the far super-Hubble limit. We present what appears to be substantial evidence, according to the Jeffreys’ scale, for a new length scale around 2200 Mpc ($k^{-1}\sim 350\mathrm{Mpc}$) above which the primordial (scalar) power spectrum is sharply reduced by about 20%.

• Received 28 January 2019
• Revised 29 May 2019

DOI:https://doi.org/10.1103/PhysRevD.100.043506