Scale-dependent galaxy bias, CMB lensing-galaxy cross-correlation, and neutrino masses

One of the most powerful cosmological data sets when it comes to constraining neutrino masses is represented by galaxy power spectrum measurements, P₆₆ (k). The constraining power of P₆₆ (k) is however severely limited by uncertainties in the modeling of the scale-dependent galaxy bias b (k). In this work we present a new proof-of-principle for a method to constrain b (k) by using the cross-correlation between the cosmic microwave background (CMB) lensing signal and galaxy maps (C_^) using a simple but theoretically well-motivated parametrization for b (k). We apply the method using C_^ measured by cross-correlating Planck lensing maps and the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 11 (DR11) CMASS galaxy sample, and P₆₆ (k) measured from the BOSS DR12 CMASS sample. We detect a nonzero scale-dependence at moderate significance, which suggests that a proper modeling of b (k) is necessary in order to reduce the impact of nonlinearities and minimize the corresponding systematics. The accomplished increase in constraining power of P₆₆ (k) is demonstrated by determining a 95% confidence level upper bound on the sum of the three active neutrino masses M_ of M_<0. 19 eV. This limit represents a significant improvement over previous bounds with comparable data sets. Our method will prove especially powerful and important as future large-scale structure surveys will overlap more significantly with the CMB lensing kernel providing a large cross-correlation signal.