Decaying Neutrinos and Large-Scale Structure Formation

Abstract

We study the growth of density perturbations in a universe with unstable dark matter particles. The mass (m nu ) range 30 eV <= m nu <= 10 keV with lifetimes (td) in the range 107 s <= td <= 1016 s are considered. We calculate the COBE normalized matter power spectrum for these models. We find that it is possible to construct models consistent with observations for masses m nu > 50 eV by adjusting td so as to keep the quantity m2_ν({keV})td({yr}) constant at a value around 100. For m nu <= 1 keV, the power spectrum has extra power at small scales that could result in an early epoch of galaxy formation. We do not find any value of td that gives a viable model in the mass range m nu <= 50 eV. We also consider the implications of radiatively decaying neutrinos--models in which a small fraction B << 1 of neutrinos decay into photons--that could possibly ionize the intergalactic medium (IGM) at high redshift. We show that the parameter space of decaying particles that satisfies the IGM observations does not give viable models of structure formation.