Enhanced Muonization by Active-Sterile Neutrino Mixing in Protoneutron Stars

We study ν_μ-νₛ and ν_μ-νₛ mixing in the protoneutron star (PNS) created in a core-collapse supernova (CCSN). We point out the importance of the feedback on the general composition of the PNS in addition to the obvious feedback on the ν_μ lepton number. We show that for our adopted mixing parameters δ m²~ 10²\,keV² and sin² 2θ consistent with the current constraints, sterile neutrino production is dominated by the Mikheyev$-$Smirnov$-$Wolfenstein conversion of ν_μ into νₛ and that the subsequent escape of νₛ increases the ν_μ lepton number, which in turn enhances muonization of the PNS primarily through ν_μ+n→ p+μ⁻. We find that this enhancement is amplified by diffusion of the νₑ and ν_μ lepton numbers. While these results are qualitatively robust, their quantitative effects on the dynamics and active neutrino emission of CCSNe should be evaluated by including ν_μ-νₛ and ν_μ-νₛ mixing in the simulations.