Scale-dependent galaxy bias, CMB lensing-galaxy cross-correlation, and
  neutrino masses
  One of the most powerful cosmological datasets when it comes to constraining
neutrino masses is represented by galaxy power spectrum measurements,
$P_{gg}(k)$. The constraining power of $P_{gg}(k)$ is however severely limited
by uncertainties in the modeling of the scale-dependent galaxy bias $b(k)$. In
this Letter we present a new method to constrain $b(k)$ by using the
cross-correlation between the Cosmic Microwave Background (CMB) lensing signal
and galaxy maps ($C_\ell^{\rm \kappa g}$) using a simple but theoretically
well-motivated parametrization for $b(k)$. We apply the method using
$C_\ell^{\rm \kappa g}$ measured by cross-correlating Planck lensing maps and
the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 11 (DR11) CMASS
galaxy sample, and $P_{gg}(k)$ measured from the BOSS DR12 CMASS sample. We
detect a non-zero scale-dependence at moderate significance, which suggests
that a proper modeling of $b(k)$ is necessary in order to reduce the impact of
non-linearities and minimize the corresponding systematics. The accomplished
increase in constraining power of $P_{gg}(k)$ is demonstrated by determining a
95% C.L. upper bound on the sum of the three active neutrino masses $M_{\nu}$
of $M_{\nu}<0.19\, {\rm eV}$. This limit represents a significant improvement
over previous bounds with comparable datasets. 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.
