Tom Charnock (University of Nottingham, United Kingdom)
There is a tension between measurements of the amplitude of the power spectrum of density perturbations inferred using the Cosmic Microwave Background (CMB) and directly measured by Large-Scale Structure (LSS) on smaller scales. We show that this tension exists, and is robust, for a range of LSS indicators including clusters, lensing and redshift space distortions and using CMB data. One obvious way to try to reconcile this is the inclusion of a massive neutrino which could be either active or sterile. Using Planck and a combination of LSS data we find that (i) for an active neutrino the sum of the neutrinos is m=(0.357+-0.99) eV and (ii) for a sterile neutrino m_sterile= (0.67+-0.18) eV and N_eff= 0.32+-0.20. This is, however, at the expense of a degraded fit to Planck temperature data, and we quantify the residual tension at 2.5- and 1.6-sigma for massive and sterile neutrinos respectively. We also consider alternative explanations including a lower redshift for reionization that would be in conflict with polarisation measurements made by WMAP and ad-hoc modications to primordial power spectrum.