The impact of a new median statistics $H_0$ prior on the evidence for dark radiation

• Main Authors: Calabrese, Erminia, Archidiacono, Maria, Melchiorri, Alessandro, Ratra, Bharat
• Format: Text
• Language: unknown
• Published: arXiv 2012
• Subjects: Cosmology and Nongalactic Astrophysics astro-ph.CO; High Energy Physics - Phenomenology hep-ph; High Energy Physics - Theory hep-th; FOS Physical sciences; South Pole; Hubble; South pole
• Online Access: https://dx.doi.org/10.48550/arxiv.1205.6753; https://arxiv.org/abs/1205.6753

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 $Λ$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. : 8 pages, 4 figures