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 $\nu_e\bar{\nu}_e$-pairs to $\nu_{\mu}\bar{\nu}_{\mu}/\nu_{\tau}\bar{\nu}_{\tau}$-pairs is $\sim$\,5-to-1. This is because at SMS temperature scales, $\nu_e\bar{\nu}_e$ pairs have both charged and neutral current production channels, whereas $\nu_{\mu}\bar{\nu}_{\mu}/\nu_{\tau}\bar{\nu}_{\tau}$-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, $\Delta m^2_\mathrm{atm.}\sim2.4\times10^{-3}$ eV$^2$. In the normal neutrino mass hierarchy, adiabatic flavor transformation through the MSW resonances would then swap the fluxes $\nu_e\leftrightharpoons\nu_{\mu,\tau}$, whereas, in the inverted neutrino mass hierarchy, the anti-neutrino fluxes are swapped, $\bar{\nu}_e\leftrightharpoons\bar{\nu}_{\mu,\tau}$. 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.