Fast Neutrino Flavor Conversions Can Help and Hinder Neutrino-Driven Explosions

We present the first simulations of core-collapse supernovae in axial symmetry with feedback from fast neutrino flavor conversion (FFC). Our schematic treatment of FFCs assumes instantaneous flavor equilibration under the constraint of lepton-number conservation individually for each flavor. Systematically varying the spatial domain where FFCs are assumed to occur, we find that they facilitate SN explosions in low-mass ($9–12M_{\odot }$) progenitors that otherwise explode with longer time delays, whereas FFCs weaken the tendency to explode of higher-mass (around $20M_{\odot }$) progenitors.

Figure 1

Angle-averaged shock radii (top) and PNS radii (bottom; defined at $\rho ={10}^{11}\mathrm{g}{\mathrm{cm}}^{-3}$) vs postbounce time for the indicated models. Black solid lines: Models noFC (no flavor conversions). Colored solid lines: Instantaneous FFCs for $\rho <{\rho }_{\mathrm{c}}$ as labeled in the legend. The unsteady motion of the average shocks with contraction and expansion phases is caused by the violent large-scale convective mass flows in the neutrino heated gain layer behind the CCSN shock. The sudden growth of $r_{\text{shock}}$ (small at $\sim 100\mathrm{ms}$ for $M9.0\text{−}2\mathrm{D}$ and prominent at $\sim 70\mathrm{ms}$ for $M11.2\text{−}2\mathrm{D}$ and at $\sim 220\mathrm{ms}$ for $M20.0\text{−}2\mathrm{D}$) signals a decrease of mass accretion rate due to the arrival of the $\mathrm{Si}/\mathrm{O}$ interface. For the noFC models, we also show the angle-averaged gain radius (dashed black) and the mean radii for $\rho ={10}^9$ and ${10}^{10}\mathrm{g}{\mathrm{cm}}^{-3}$ (dash-dotted and dotted black lines , respectively), all smoothed with 10 ms running averages. For the 9.0 and $11.2M_{\odot }$ progenitors, FFCs support an earlier onset of the explosion, whereas for $20.0M_{\odot }$ they thwart it and the shock recedes even more rapidly.

Figure 2

Total net neutrino-heating rate (top), mass in the gain layer (middle), and net heating rate per baryon (bottom) for our $M11.2–2\mathrm{D}$ simulations. (10 ms running average.).

Figure 3

Evolution of luminosities and mean energies of the radiated ${\nu }_e$, ${\overline{\nu }}_e$, and one species of ${\nu }_x$ for our $M11.2\text{−}2\mathrm{D}$ simulations. All quantities are angle averaged, measured at a radius of 500 km, and transformed to a distant observer at rest.

Figure 4

Mass accretion rates at 400 km for the noFC models. The steplike features (arrows) derive from density jumps at the $\mathrm{Si}/\mathrm{O}$ interfaces of the collapsing progenitors.