Neutrino Physics from the Cosmic Microwave Background and Large Scale Structure

The cosmological background of neutrinos thermally produced in the big bang has been definitively (albeit indirectly) detected. Measurements of the cosmic microwave background (CMB) alone have led to a constraint on the effective number of neutrino species of Neff = 3.36 ± 0.34 [1], a value 10σ away from zero and consistent with expectations. Experiments planned and underway are prepared to study this background in detail via its influence on distance-redshift relations and the growth of structure. The program for the next decade described in this document, including upcoming spectroscopic surveys eBOSS and DESI and a new Stage-IV CMB polarization experiment CMB-S4, will achieve σ( mν) = 16 meV and σ(Neff) = 0.020. Such a mass measurement will produce a high significance detection of non-zero mν, whose lower bound derived from atmospheric and solar neutrino oscillation data is about 58 meV. If neutrinos have a normal mass hierarchy, this measurement will definitively rule out the inverted neutrino mass hierarchy, shedding light on one of the most puzzling aspects of the Standard Model of particle physics – the origin of mass. This precise a measurement ofNeff will allow for a precision test of the standard cosmological model predictio