A comment on power-law inflation with a dark radiation component

TL;DR

This paper critically examines a proposed power-law inflation model with dark radiation, showing it does not resolve the $\sigma_8$ tension and the $H_0$ tension reemerges with new data, reducing its viability.

Contribution

The paper provides a critical analysis of the power-law inflation with dark radiation proposal, highlighting its limitations in resolving key cosmological tensions.

Findings

Does not resolve the $\sigma_8$ tension.

Reintroduces the $H_0$ tension with latest Planck data.

Reduces the scenario's appeal as a solution.

Abstract

Tram et al. 2016 recently pointed out that power-law inflation in presence of a dark radiation component may relieve the 3.3 sigma tension which exists within standard LCDM between the determination of the local value of the Hubble constant by Riess et al. (2016) and the value derived from CMB anisotropy data by the Planck collaboration. In this comment, we simply point out that this interesting proposal does not help in solving the $\sigma_8$ tension between the Planck data and, e.g., the weak lensing measurements. Moreover, when the latest constraints on the reionization optical depth obtained from Planck HFI data are included in the analysis, the $H_0$ tension reappears and this scenario looses appeal.