What is half a neutrino? Reviewing cosmological constraints on neutrinos and dark radiation

Abstract

Neutrinos are one of the major puzzles in modern physics. Despite measurements of mass differences, the Standard Model of particle physics describes them as exactly massless. Additionally, recent measurements from both particle physics experiments and cosmology indicate the existence of more than the three Standard Model species. Here we review the cosmological evidence and its possible interpretations.

15 pages, 4 figures, invited review accepted for publication in PASA

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• Updated CMB, X- and gamma-ray constraints on majoron dark matter
• Neutrino Flavor Conversions in High-Density Astrophysical and Cosmological Environments
• A robust deuterium abundance; Re-measurement of the z=3.256 absorption system towards the quasar PKS1937-1009
• Multi-momentum and multi-flavour active-sterile neutrino oscillations in the early universe: role of neutrino asymmetries and effects on nucleosynthesis
• Combining Planck with Large Scale Structure gives strong neutrino mass constraint
• The WiggleZ Dark Energy Survey: Final Data Release and the Metallicity of UV-Luminous Galaxies
• Light Sterile Neutrinos: Status and Perspectives
• Is there evidence for additional neutrino species from cosmology?
• Constraints on neutrino masses from the study of the nearby large-scale structure and galaxy cluster counts
• Cosmological evidence for leptonic asymmetry after Planck
• Two sides of the same coin: sterile neutrinos and dark radiation. Status and perspectives
• Reionization during the dark ages from a cosmic axion background
• CMB signature of non-thermal Dark Matter produced from self-interacting dark sector
• Cosmological Constraints on 4-Dimensional Einstein-Gauss-Bonnet Gravity
• Measurement of the matter-radiation equality scale using the extended Baryon Oscillation Spectroscopic Survey Quasar Sample
• A Cosmic ALP Background and the Cluster Soft X-ray Excess in A665, A2199 and A2255
• Light sterile neutrino sensitivity of 163Ho experiments
• Using peculiar velocity surveys to constrain neutrino masses
• Lepton Asymmetry and Neutrino Oscillations Interplay
• Asymmetric dark matter and effective number of neutrinos
• On the baryon acoustic oscillation amplitude as a probe of radiation density
• A Sterile Neutrino Search at compact materials irradiation facility