Impact of H_{0} prior on the evidence for dark radiation

• Published in: Physical Review D
• Main Authors: CALABRESE, ERMINIA, MELCHIORRI, Alessandro, Maria Archidiacono, Ratra Bharat
• Other Authors: Calabrese, Erminia, Maria, Archidiacono, Melchiorri, Alessandro, Ratra, Bharat
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2012
• Subjects: Hubble; South Pole; South pole
• Online Access: http://hdl.handle.net/11573/488209; https://doi.org/10.1103/physrevd.86.043520

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 Hubble Space Telescope prior on the Hubble constant, where H0=73.8±2.4 km/s/Mpc at 68% c.l. Here we repeat this kind of analysis assuming a prior of H0=68±2.8 km/s/Mpc at 68% c.l., derived from a median statistics (MS) analysis of 537 non-CMB H0 measurements from Huchra’s compilation. This prior is fully consistent with the value of H0=69.7±2.5 km/s/Mpc at 68% c.l. obtained from CMB measurements under assumption of the standard ΛCDM model. We show that with the MS H0 prior the evidence for dark radiation is weakened to ∼1.2 standard deviations. Parametrizing the dark radiation component through the effective number of relativistic degrees of freedom Neff, we find Neff=3.98±0.37 at 68% c.l. with the Hubble Space Telescope prior and Neff=3.52±0.39 at 68% c.l. with the MS prior. We also discuss the implications for current limits on neutrino masses and on primordial Helium abundances.