Abstract
Neutrino oscillation experiments point towards the existence of additional mostly sterile neutrino mass eigenstates in the eV mass range. At the same time, such sterile neutrinos are disfavoured by cosmology (Big Bang Nucleosynthesis, Cosmic Microwave Background and Large Scale Structure), unless they can be prevented from being thermalised in the early Universe. To this aim, we introduce a model of sterile neutrino secret interactions mediated by a new light pseudoscalar: The new interactions can accomodate sterile neutrinos in the early Universe, providing a good fit to all the up to date cosmological data.
Highlights
Neutrinos deeply affect the cosmological observables, such as the Cosmic Microwave Background and the power spectrum of matter fluctuations
In the last decade oscillation data have been providing hints of the existence of one sterile neutrinos in the eV mass range [2, 3, 4], while the latest Planck results [1] rule out additional neutrino species at high significance
We present a pseudoscalar model of secret interactions which satisfies all the cosmological constraints on sterile neutrinos
Summary
Neutrinos deeply affect the cosmological observables, such as the Cosmic Microwave Background and the power spectrum of matter fluctuations. We present a pseudoscalar model of secret interactions which satisfies all the cosmological constraints on sterile neutrinos. 2. Model framework and early Universe phenomenology The new non-standard Lagrangian term describing the secret interaction between sterile neutrinos and pseudoscalars is given by
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