Tickling the CMB damping tail: scrutinizing the tension between the ACT
  and SPT experiments
  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 or coupled dark energy. 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 tension at more
than 95% c.l..
