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