Note on Thermalization of Non-resonantly Produced Sterile Neutrinos.

In this addendum to the article JCAP 1912 (2019) no.12, 047 (arXiv:1909.13328) on the cosmological dependence of non-resonantly produced sterile neutrinos we discuss, using an analytic treatment, the parameter regions of large active-sterile neutrino mixing angles where sterile neutrinos can approach thermalization. We show that these additional considerations affect only large active-sterile neutrino mixing already rejected by different limits. Hence, the allowed sterile neutrino parameter regions are unaffected.