Mu-Tau Neutrinos: Influencing Fast Flavor Conversions in Supernovae

Neutrinos in a core-collapse supernova can undergo fast flavor conversions with a possible impact on the explosion mechanism and nucleosynthesis. We perform the first nonlinear simulations of fast conversions in the presence of three neutrino flavors. The recent supernova simulations with muon production call for such an analysis, as they relax the standard ${\nu }_{\mu ,\tau }={\overline{\nu }}_{\mu ,\tau }$ (two-flavor) assumption. Our results show the significance of muon and tau lepton number angular distributions, together with the traditional electron lepton number ones. Indeed, our three-flavor results are potentially very different from two-flavor ones. These results strengthen the need to further investigate the occurrence of fast conversions in supernova simulation data, including the degeneracy breaking of mu and tau neutrinos.

Figure 1

The upper panels show the angular distribution of the fluxes and the effective lepton numbers for different flavors. The effective lepton number panel ($G_{\mathbf{v}}^{\alpha \beta }$ vs $\mathbf{v}$) shows both the three-flavor (solid lines) and the two-flavor ELN (dashed line). The lower panel shows the evolution of the angle-averaged off-diagonal elements $|⟨{\rho }_{\alpha \beta }⟩|$ of the density matrix with time (in ns). The three-flavor evolution (solid lines) has no instability, while the effective two-flavor evolution, assuming ${\nu }_x={\overline{\nu }}_x$, shows large exponential growth (dashed line).

Figure 2

Panels represent same as in Fig. 1. However, due to large crossings in $G_{\mathbf{v}}^{e\mu }$, $G_{\mathbf{v}}^{e\tau }$, substantial flavor conversions are seen in all the sectors.

Figure 3

Panels represent same as in Fig. 1. Crossing only in $G_{\mathbf{v}}^{\mu \tau }$ causes an exponential growth in $\mu -\tau$ sector (lower panel). The two-flavor evolution shows no instability.

Figure 4

Panels represent same as in Fig. 1. However, shallow crossings are present in $G_{\mathbf{v}}^{e\mu }$, $G_{\mathbf{v}}^{e\tau }$ in the backward direction (upper panels), leading to exponential growths in $|⟨{\rho }_{\alpha \beta }⟩|$ (lower panel) for the three-flavor setup. The two-flavor evolution shows no instability.