Constraints on the running of the running of the scalar tilt from CMB anisotropies and spectral distortions
Résumé
We use the recent observations of cosmic microwave background (CMB) temperature and polarization anisotropies provided by the Planck satellite experiment to place constraints on the running αs=d ns/d log k and the running of the running βs=d αs/d log k of the spectral index ns of primordial scalar fluctuations. We find αs=0.011 ±0.010 and βs=0.027 ±0.013 at 68% C.L., suggesting the presence of a running of the running at the level of two standard deviations. We find no significant correlation between βs and foregrounds parameters, with the exception of the point sources amplitude at 143 GHz, A143PS , which shifts by a half-sigma when the running of the running is considered. We further study the cosmological implications of such a preference for αs,βs∼0.01 by including in the analysis the lensing amplitude AL, the curvature parameter Ωk, and the sum of neutrino masses ∑mν. We find that when the running of the running is considered Planck data are more compatible with the standard expectations of AL=1 and Ωk=0 but still hint at possible deviations. The indication for βs>0 survives at two standard deviations when external data sets such as baryon acoustic oscillation surverys and CFHTLenS are included in the analysis and persists at ∼1.7 standard deviations when CMB lensing is considered. We discuss the possibility of constraining βs with current and future measurements of CMB spectral distortions, showing that an experiment like PIXIE could provide strong constraints on αs and βs.
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