Thermalisation of light sterile neutrinos in the early universe

By S. Hannestad, I. Tamborra, T. Tram. 2012

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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 νs 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 −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.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b5da9507779ce60919fe1e2e6a579b074c75472b

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Citations in the corpus

A White Paper on keV sterile neutrino Dark Matter (2016, background): “The first one is represented by the introduction of a primordial neutrino-antineutrino asymmetry term [299, 300] in the equations for the flavor evolution (see eqs.”
The Phenomenology of Right Handed Neutrinos (2013, background): “Quantitative studies of the flavour evolution [255, 257–259, 355–357] are required to answer the question to which degree a lepton chemical potential can prevent the thermalization [278, 334, 353, 354, 358–366].”
Neutrino Mass from Cosmology (2012, background): “ton asymmetry and m2 s>0 (left panel) and m2s <0 (right pannel). The star denotes the best-t mixing parameters as in the 3+1 global t in [37]: (m2;sin2 2 s) = (0:9 eV2;0:089). Adapted from [38]. Courtesy of S. Hannestad, I. Tamborra, and T. Tram. s is larger than the expansion rate of the Uni”