Neutrino Flavor Transformation in Collapsing Supermassive Objects

Abstract

The collapse of supermassive stars (SMSs, $M\gtrsim10^4\,M_\odot$) to black holes is accompanied by a prodigious flux of neutrinos of all flavors. These are produced thermally via $e^\pm$ annihilations, mostly in the core and just before gravitational trapped surface formation. There, the ratio of fluxes for $ν_e\barν_e$-pairs to $ν_μ\barν_μ/ν_τ\barν_τ$-pairs is $\sim$\,5-to-1. This is because at SMS temperature scales, $ν_e\barν_e$ pairs have both charged and neutral current production channels, whereas $ν_μ\barν_μ/ν_τ\barν_τ$-pairs only have neutral current production channels. We point out that the typical energies of these neutrinos, and the run of density in collapsing radiation-dominated supermassive configurations, leads to Mikheyev-Smirnov-Wolfenstein (MSW) resonances inside these objects for the atmospheric neutrino mass splitting scale, $Δm^2_\mathrm{atm.}\sim2.4\times10^{-3}$ eV$^2$. In the normal neutrino mass hierarchy, adiabatic flavor transformation through the MSW resonances would then swap the fluxes $ν_e\leftrightharpoonsν_{μ,τ}$, whereas, in the inverted neutrino mass hierarchy, the anti-neutrino fluxes are swapped, $\barν_e\leftrightharpoons\barν_{μ,τ}$. We also examine the prospects for collective neutrino flavor oscillations in these environments. Implications for flavor oscillation's effects on neutrino energy deposition and neutrino-induced nucleosynthesis in the SMS's outer layers are examined, as are prospects for detections of SMS collapses through various means.