Modified big bang nucleosynthesis with non-standard neutron sources

During big bang nucleosynthesis, any injection of extra neutrons around the time of the $^7$Be formation, i.e. at a temperature of order $T \simeq 50$~keV, can reduce the predicted freeze-out amount of $^7$Be + $^7$Li that otherwise remains in sharp contradiction with the Spite plateau value inferred from the observations of Pop II stars. However, the growing confidence in the primordial D/H determinations puts a strong constraint on any such scenario. We address this issue in detail, analyzing different temporal patterns of neutron injection, such as decay, annihilation, resonant annihilation, and oscillation between mirror and standard model world neutrons. For this latter case, we derive the realistic injection pattern taking into account thermal effects (damping and refraction) in the primordial plasma. If the extra neutron supply is the sole non-standard mechanism operating during the BBN, the suppression of lithium abundance below Li/H~$\leq 1.9 \times 10^{-10}$ always leads to the overproduction of deuterium, D/H~$\geq 3.6 \times 10^{-5}$, well outside the error bars suggested by recent observations.