Neutrino physics from precision cosmology
Steen Hannestad
TL;DR
The paper surveys how precision cosmology constrains neutrino properties, emphasizing the absolute mass scale and the role of neutrinos in cosmic structure formation. It discusses the standard thermal history, including neutrino decoupling, the small extra relativistic energy density $N_\nu \approx 3.046$, and flavour equilibration effects on Big Bang nucleosynthesis. It uses linear and nonlinear perturbation theory and the Boltzmann equation formalism to outline current bounds on the sum of neutrino masses and the constraints on relativistic energy density and lepton asymmetries, with future surveys potentially reaching $\sim 0.03-0.05$ eV for $\sum m_j$ and addressing the cosmic neutrino background anisotropy. The article also explains the phenomenology of neutrinos as hot dark matter, including the Tremaine-Gunn bound and the impact of free-streaming on structure formation, and highlights forthcoming observational probes and systematic challenges.
Abstract
Cosmology provides an excellent laboratory for testing various aspects of neutrino physics. Here, I review the current status of cosmological searches for neutrino mass, as well as other properties of neutrinos. Future cosmological probes of neutrino properties are also discussed in detail.