The impact of a new median statistics $H_0$ prior on the evidence for
  dark radiation
  Recent analyses that include cosmic microwave background (CMB) anisotropy
measurements from the Atacama Cosmology Telescope and the South Pole Telescope
have hinted at the presence of a dark radiation component at more than two
standard deviations. However, this result depends sensitively on the assumption
of an HST prior on the Hubble constant, where $H_0=73.8\pm2.4$ km/s/Mpc at 68%
c.l.. From a median statistics (MS) analysis of 537 non-CMB $H_0$ measurements
from Huchra's compilation we derive $H_0=68 \pm2.8$ km/s/Mpc at 68% c.l., in
good agreement with the results of a recent analysis of the full Huchra list of
$H_0$ measurements. This result is also fully consistent with the value of
$H_0=69.7\pm2.5$ km/s/Mpc at 68% c.l. obtained from CMB measurements under
assumption of the standard $\Lambda$CDM model. We show that with the MS $H_0$
prior the evidence for dark radiation is weakened to $\sim 1.2$ standard
deviations. Parametrizing the dark radiation component through the effective
number of relativistic degrees of freedom $N_{eff}$, we find
$N_{eff}=3.98\pm0.37$ at 68% c.l. with the HST prior and $N_{eff}=3.52\pm0.39$
at 68% c.l. with the MS prior. We also discuss the implications for current
limits on neutrino masses and on primordial Helium abundances.
