1301.7343 (Eleonora Di Valentino et al.)

Tickling the CMB damping tail: scrutinizing the tension between the ACT and SPT experiments    [PDF]

Eleonora Di Valentino, Silvia Galli, Massimiliano Lattanzi, Alessandro Melchiorri, Paolo Natoli, Luca Pagano, Najla Said

The Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) have recently provided new, very precise measurements of the cosmic microwave background (CMB) anisotropy damping tail. The values of the cosmological parameters inferred from these measurements, while broadly consistent with the expectations of the standard cosmological model, are providing interesting possible indications for new physics that are definitely worth of investigation. The ACT results, while compatible with the standard expectation of three neutrino families, indicate a level of CMB lensing, parametrized by the lensing amplitude parameter A_L, that is about 70% higher than expected. If not a systematic, this anomalous lensing amplitude could be produced by modifications of general relativity. Vice-versa, the SPT experiment, while compatible with a standard level of CMB lensing, prefers an excess of dark radiation, parametrized by the effective number of relativistic degrees of freedom N_eff. Here we perform a new analysis of these experiments allowing simultaneous variations in both these, non-standard, parameters. We also combine these experiments, for the first time in the literature, with the recent WMAP9 data, one at a time. Including the Hubble Space Telescope (HST) prior on the Hubble constant and information from baryon acoustic oscillations (BAO) surveys provides the following constraints from ACT: N_eff=3.23\pm0.47, A_L=1.65\pm0.33 at 68% c.l., while for SPT we have N_eff=3.76\pm0.34, A_L=0.81\pm0.12 at 68% c.l.. In particular, the A_L estimates from the two experiments, even when a variation in N_eff is allowed, are in disagreement at more than 95% c.l., suggesting the presence of systematics in at least one of the two datasets. Finally, we show that the SPT claim for a detection at 95% c.l. for a neutrino mass vanishes once variations in the lensing parameter A_L are taken into account.

View original: http://arxiv.org/abs/1301.7343