Inflation Wars: A New Hope

TL;DR

This paper introduces a new class of primordial power spectra that better fit cosmic microwave background data and reconcile the Hubble constant discrepancy by interpolating between standard and modified spectra, improving fit and expanding H_0 estimates.

Contribution

It proposes a novel deformation of primordial power spectra that enhances data fit and links to Hubble parameter estimates, addressing the H_0 tension.

Findings

Better fit to Planck data with deformed spectra (ΔlogL=2.5).

H_0 estimate shifts to 70.2 ± 1.2 km/s/Mpc.

Bayes factor strongly favors the deformation model.

Abstract

We explore a class of primordial power spectra that can fit the observed anisotropies in the cosmic microwave background well and that predicts a value for the Hubble parameter consistent with the local measurement of $H_0 = 74$ km/s/Mpc. This class of primordial power spectrum consists of a continuous deformation between the best-fit power law primordial power spectrum and the primordial power spectrum derived from the modified Richardson-Lucy deconvolution algorithm applied to the $C_\ell$s of best-fit power law primordial power spectrum. We find that linear interpolation half-way between the power law and modified Richardson-Lucy power spectra fits the Planck data better than the best-fit $\Lambda$CDM by $\Delta\log\mathcal{L} = 2.5$. In effect, this class of deformations of the primordial power spectra offer a new dimension which is correlated with the Hubble parameter. This correlation causes the best-fit value for $H_0$ to shift and the uncertainty to expand to $H_0 = 70.2 \pm 1.2$ km/s/Mpc. When considering the Planck dataset combined with the Cepheid $H_0$ measurement, the best-fit $H_0$ becomes $H_0 = 71.8 \pm 0.9$ km/s/Mpc. We also compute a Bayes factor of $\log K = 5.7$ in favor of the deformation model.