### Abstract

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 from LSST, along with key systematics parameters and Planck priors, can constrain the neutrino masses to ∑ m_{ν} = 0.041 eV at 1-σ 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 ∑ m_{ν} = 0.032 eV . These constraints are derived having marginalized over the number of relativistic species (N_{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_{eff} measurements, the mass of the dark radiation candidate can be measured at a 1-σ level of 0.162 eV for fermionic dark radiation, and 0.137 eV for bosonic dark radiation, for Δ N_{eff} = 0.15. We also find that the NNaturalness model of Arkani-Hamed et al. [1], 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.

Original language | English (US) |
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Article number | 022 |

Journal | Journal of Cosmology and Astroparticle Physics |

Volume | 2018 |

Issue number | 1 |

DOIs | |

State | Published - Jan 2018 |

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### Keywords

- cosmological neutrinos
- cosmological parameters from LSS
- neutrino masses from cosmology

### ASJC Scopus subject areas

- Astronomy and Astrophysics

### Cite this

*Journal of Cosmology and Astroparticle Physics*,

*2018*(1), [022]. https://doi.org/10.1088/1475-7516/2018/01/022