PT Journal
AU Gariazzo, S
   de Salas, PF
   Pastor, S
TI Thermalisation of sterile neutrinos in the early universe in the 3+1 scheme with full mixing matrix
SO Journal of Cosmology and Astroparticle Physics
JI J. Cosmol. Astropart. Phys.
PY 2019
BP 014
EP 30pp
VL 07
IS 7
DI 10.1088/1475-7516/2019/07/014
LA English
DE cosmological neutrinos; neutrino properties; particle physics – cosmology connection; physics of the early universe
AB In the framework of a 3+1 scheme with an additional inert state, we consider the thermalisation of sterile neutrinos in the early Universe taking into account the full 4 x 4 mixing matrix. The evolution of the neutrino energy distributions is found solving the momentum-dependent kinetic equations with full diagonal collision terms, as in previous analyses of flavour neutrino decoupling in the standard case. The degree of thermalisation of the sterile state is shown in terms of the effective number of neutrinos, N-eff, and its dependence on the three additional mixing angles (theta(14), theta(24), theta(34)) and on the squared mass difference Delta m(41)(2) is discussed. Our results are relevant for fixing the contribution of a fourth light neutrino species to the cosmological energy density, whose value is very well constrained by the final Planck analysis. For the preferred region of active-sterile mixing parameters from short-baseline neutrino experiments, we find that the fourth state is fully thermalised (N-eff similar or equal to 4).
ER