1507.06646
Beyond six parameters: extending $\Lambda$ CDM
Di Valentino, Melchiorri, Silk
Cosmological constraints are usually derived under the assumption of a 6 parameters LCDM theoretical framework or simple one-parameter extensions. In this paper, present for the first time cosmo constraints in a significantly extended scenario, varying up to 12 cosmo parameters simultaneously, including the sum of neutrino masses, the neutrino effective number, the DE EoS, the gravitational waves background and the running of the spectral index of primordial perturbations. Using the latest Planck 2015 data release (with polarization) find no significant indication for extensions to the standard LCDM scenario, with the notable exception of the angular power spectrum lensing amplitude, A_lens that is larger than the expected value at more than 2 std. dev. even when combining the Planck data with BAO and SNIa external datasets. In the extended cosmo framework, find that a combined Planck+BAO analysis constrains the value of the r.m.s. density fluctuation parameter to sigma8=0.781±0.065 at 95% c.l., helping to relieve the possible tensions with the CFHTLenS cosmic shear survey. Also find a lower value for the reionization optical depth tau=0.058±0.040 at 95% c.l. respect to the one derived under the assumption of LCDM. The scalar spectral index n_s is now compatible with Harrison-Zeldovich spectrum to within 2.5 std. dev. Combining the Planck data set with the HST prior on the Hubble constant provides a value for the EoS w<-1 at more than 2 std deviations while the neutrino effective number is fully compatible with the expectations of the standard 3 neutrino framework.
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