  We discuss how a laboratory detection of a sterile neutrino not only would
constitute a fundamental discovery of a new particle, but could also provide an
indication of the evolution of the Universe before Big-Bang Nucleosynthesis
(BBN), a fundamental discovery in cosmology. These "visible" sterile neutrinos
could be detected in experiments such as KATRIN/TRISTAN and HUNTER in the keV
mass range and PTOLEMY, KATRIN and reactor neutrino experiments in the eV mass
range. Standard assumptions are usually made to compute the relic abundance and
momentum distribution of particles produced before the temperature of the
Universe was 5 MeV, an epoch from which there are no observed remnants thus
far. However, non-standard pre-BBN cosmologies based on other assumptions that
are equally in agreement with all existing data can arise in some theoretical
models. We revisit the production of 0.01 eV to 1 MeV sterile neutrinos via
non-resonant active-sterile flavor oscillations in several pre-BBN cosmologies.
We give general equations for models in which the expansion of the Universe is
parametrized by its amplitude and temperature power and where entropy is
conserved, which include kination and scalar tensor models as special cases.

High Energy Physics - Phenomenology;Cosmology and Nongalactic Astrophysics;High Energy Physics - Experiment