Abstract
We study the effects of kination and scalar-tensor pre-Big Bang Nucleosynthesis cosmologies on the non-resonant production of sterile neutrinos. We show that if the peak of the production rate of sterile neutrinos occurs during a non-standard cosmological phase, the relic number density of sterile neutrinos could be reduced with respect to the number expected in the standard cosmology. Consequently, current bounds on active-sterile neutrino mixing derived from the relic energy density of sterile neutrinos could be greatly relaxed. In particular, we show that the sterile neutrinos which could explain the anomalies found in short-baseline neutrino experiments are compatible with recent joint Planck upper limits on their contribution to the energy density of the Universe in a scalar-tensor or a low-reheating temperature pre-Big Bang Nucleosynthesis cosmology.
Highlights
Where the sum is over sterile neutrino species, and nνα is the number density of an active neutrino
This paper considers the effects of kination and scalar-tensor pre-Big Bang Nucleosynthesis (BBN) cosmologies on sterile neutrinos
In this paper we presented the effects of some non-standard pre-BBN cosmologies on the production of sterile neutrinos
Summary
The early Universe is radiation dominated, and the expansion rate of the Universe is given by HST D = πT 2/MP g /90, where T is the temperature of the radiation bath, MP is the reduced Planck mass, and g is the number of relativistic degrees of freedom. Scalar-tensor theories of gravity [47, 48] have a scalar field coupled through the metric tensor to the matter fields This scalar field changes the expansion rate of the Universe before the thermal bath has the transition temperature Ttr, after which the theory is indistinguishible from General Relativity. In low reheating temperature models, a scalar field φ oscillating around its true minimum while decaying dominates the energy density of the Universe just before Big Bang. After the decay of φ, radiation dominates the energy density of the Universe This case, which we include only for comparison, was studied in Refs. This case, which we include only for comparison, was studied in Refs. [22] and [23]
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