Massive sterile neutrinos in the early universe: From thermal decoupling to cosmological constraints

Abstract

We consider relatively heavy neutrinos ${\nu }_H$, mostly contributing to a sterile state ${\nu }_s$, with mass in the range 10 MeV $\lesssim m_s\lesssim m_{\pi }\sim 135$ MeV, which are thermally produced in the early universe in collisional processes involving active neutrinos, and freezing out after the QCD phase transition. If these neutrinos decay after the active neutrino decoupling, they generate extra neutrino radiation, but also contribute to entropy production. Thus, they alter the value of the effective number of neutrino species $N_{\mathrm{eff}}$ as for instance measured by the cosmic microwave background (CMB), as well as affect primordial nucleosynthesis (BBN), notably ${}^4$He production. We provide a detailed account of the solution of the relevant Boltzmann equations. We also identify the parameter space allowed by current Planck satellite data and forecast the parameter space probed by future Stage-4 ground-based CMB observations, expected to match or surpass BBN sensitivity.

V2: 28 pages, 16 figures, references updated, minor clarifications in figures and text according to version published in PRD

References in corpus (6)

• Primordial Nucleosynthesis: from precision cosmology to fundamental physics
• CMB-S4 Science Case, Reference Design, and Project Plan
• Feebly-Interacting Particles:FIPs 2020 Workshop Report
• Improved BBN constraints on Heavy Neutral Leptons
• Heavy sterile neutrino emission in core-collapse supernovae: Constraints and signatures
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Cited by in corpus (16)

• The Present and Future Status of Heavy Neutral Leptons
• Neutrino Flavor Conversions in High-Density Astrophysical and Cosmological Environments
• Mapping the viable parameter space for testable leptogenesis
• Comprehensive constraints on heavy sterile neutrinos from core-collapse supernovae
• 511 keV line constraints on feebly interacting particles from supernovae
• Constraining the primordial black hole abundance through Big-Bang nucleosynthesis
• Primordial neutrinos and new physics: novel approach to solving neutrino Boltzmann equation
• New physics decaying into metastable particles: impact on cosmic neutrinos
• How new physics affects primordial neutrinos decoupling: Direct Simulation Monte Carlo approach
• In-flight positron annihilation as a probe of feebly interacting particles
• Low-scale leptogenesis with flavour and CP symmetries
• Dynamics of metastable Standard Model particles from long-lived particle decays in the MeV primordial plasma
• Non-Minimal Approximation for the Type-I Seesaw Mechanism
• Possible Impact of non-Gaussianities on cosmological constraints in neutrino physics
• Axion signatures from supernova explosions through the nucleon electric-dipole portal
• Cosmic Overture Echoed in a Stellar Final Act: Implications of Nanohertz Gravitational Waves for Core Collapse Supernova Neutrinos