Thermalisation of light sterile neutrinos in the early universe
- Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C (Denmark)
- Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, 80805 München (Germany)
Recent cosmological data favour additional relativistic degrees of freedom beyond the three active neutrinos and photons, often referred to as ''dark'' radiation. Light sterile neutrinos is one of the prime candidates for such additional radiation. However, constraints on sterile neutrinos based on the current cosmological data have been derived using simplified assumptions about thermalisation of ν{sub s} at the Big Bang Nucleosynthesis (BBN) epoch. These assumptions are not necessarily justified and here we solve the full quantum kinetic equations in the (1 active + 1 sterile) scenario and derive the number of thermalised species just before BBN begins (T ≅ 1 MeV) for null (L = 0) and large (L = 10{sup −2}) initial lepton asymmetry and for a range of possible mass-mixing parameters. We find that the full thermalisation assumption during the BBN epoch is justified for initial small lepton asymmetry only. Partial or null thermalisation occurs when the initial lepton asymmetry is large.
- OSTI ID:
- 22279844
- Journal Information:
- Journal of Cosmology and Astroparticle Physics, Vol. 2012, Issue 07; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1475-7516
- Country of Publication:
- United States
- Language:
- English
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