Cosmological neutrinos
Steen Hannestad
TL;DR
This review surveys how cosmological data constrain neutrino properties, focusing on late-time effects of neutrinos on the cosmic microwave background and large-scale structure. It integrates standard-model decoupling physics, BBN constraints, and oscillation phenomena to bound the total neutrino energy density, the effective number of neutrino species $N_\nu$, and the absolute mass scale, including implications for sterile neutrinos and neutrino dark matter. The work highlights how joint analyses of CMB, LSS, BBN, and other datasets reveal a cosmological neutrino background and place stringent limits on neutrino masses, with consequences for structure formation and the viability of neutrinos as dark matter candidates. Overall, neutrinos leave measurable imprints on early- and late-time cosmology, enabling precise bounds on their properties and informing particle physics beyond the standard model.
Abstract
The current status of neutrino cosmology is reviewed, from the question of neutrino decoupling and the presence of sterile neutrinos to the effects of neutrinos on the cosmic microwave background and large scale structure. Particular emphasis is put on cosmological neutrino mass measurements.