Neutrinos in Cosmology

TL;DR

This paper reviews the role of neutrinos in cosmology, discussing their decoupling, constraints on their properties, mass hierarchy, and prospects for direct detection of relic neutrinos, highlighting their importance in understanding universe evolution.

Contribution

It provides a comprehensive overview of neutrino cosmology, including recent constraints on neutrino properties and future detection prospects, integrating particle physics and cosmological observations.

Findings

Current cosmological bounds tightly constrain neutrino masses.

Neutrino mass hierarchy influences future laboratory experiments.

Potential for direct detection of cosmic relic neutrinos is discussed.

Abstract

Neutrinos are the least known particle in the Standard Model of elementary particle physics. They play a crucial role in cosmology, governing the universe's evolution and shaping the large-scale structures we observe today. In this chapter, we review crucial topics in neutrino cosmology, such as the neutrino decoupling process in the very early universe. We shall also revisit the current constraints on the number of effective relativistic degrees of freedom and the departures from its standard expectation of 3. Neutrino masses represent the very first departure from the Standard Model of elementary particle physics and may imply the existence of new unexplored mass generation mechanisms. Cosmology provides the tightest bound on the sum of neutrino masses, and we shall carefully present the nature of these constraints, both on the total mass of the neutrinos and on their precise spectrum. The ordering of the neutrino masses plays a major role in the design of future neutrino mass searches from laboratory experiments, such as neutrinoless double beta decay probes. Finally, we shall also present the futuristic perspectives for an eventual direct detection of cosmic, relic neutrinos.