MeV-scale reheating temperature and thermalization of oscillating
  neutrinos by radiative and hadronic decays of massive particles
  From a theoretical point of view, there is a strong motivation to consider an
MeV-scale reheating temperature induced by long-lived massive particles with
masses around the weak scale, decaying only through gravitational interaction.
In this study, we investigate lower limits on the reheating temperature imposed
by big-bang nucleosynthesis assuming both radiative and hadronic decays of such
massive particles. For the first time, effects of neutrino self-interactions
and oscillations are taken into account in the neutrino thermalization
calculations. By requiring consistency between theoretical and observational
values of light element abundances, we find that the reheating temperature
should conservatively be $T_{\rm RH} \gtrsim 1.8$ MeV in the case of the 100%
radiative decay, and $T_{\rm RH} \gtrsim$ 4-5 MeV in the case of the 100%
hadronic decays for particle masses in the range of 10 GeV to 100 TeV.
