Tests of Neutrino and Dark Radiation Models from Galaxy and CMB surveys
  We analyze the ability of galaxy and CMB lensing surveys to constrain massive
neutrinos and new models of dark radiation. We present a Fisher forecast
analysis for neutrino mass constraints with the LSST galaxy survey and the CMB
S4 survey. A joint analysis of the three galaxy and shear 2-point functions,
along with key systematics parameters and Planck priors, constrains the
neutrino masses to $\sum m_\nu = 0.041\,$eV at 1-$\sigma$ level, comparable to
constraints expected from Stage 4 CMB lensing. If low redshift information from
upcoming spectroscopic surveys like DESI is included, the constraint becomes
$\sum m_\nu = 0.032\,$eV. These constraints are derived having marginalized
over the number of relativistic species ($N_{\rm eff}$), which is somewhat
degenerate with the neutrino mass. We also explore the gain by combining LSST
and CMB S4, that is, using the five relevant auto- and cross-correlations of
the two datasets. We conclude that advances in modeling the nonlinear regime
and the measurements of other parameters are required to ensure a neutrino mass
detection. Using the same datasets, we explore the ability of LSST-era surveys
to test "nonstandard" models with dark radiation. We find that if evidence for
dark radiation is found from $N_{\rm eff}$ measurements, the mass of the dark
radiation candidate can be measured at a 1-$\sigma$ level of $0.162\,$eV for
fermionic dark radiation, and $0.137\,$eV for bosonic dark radiation, for
$\Delta N_{\rm eff} = 0.15$. We also find that the NNaturalness model of
Arkani-Hamed et al 2016, with extra light degrees of freedom, has a sub-percent
effect on the power spectrum: even more ambitious surveys than the ones
considered here will be needed to test such models.
