Abstract
Abstract
Our understanding of neutrino flavor conversion in the supernova core is still
preliminary, despite its likely relevance to the neutrino-driven supernova mechanism. We present
multi-angle and multi-energy numerical simulations of neutrino quantum kinetics within a
spherically symmetric shell in the proximity of the region of neutrino decoupling. We rely on
inputs from a one-dimensional core-collapse supernova model with a mass of 18.6 M
⊙ and
find that, at early post-bounce times (t
pb ≲ 0.5 s), no crossing is present in
the angular distribution of the electron neutrino lepton number and flavor conversion is triggered
by slow collective instabilities. Angular crossings appear for t
pb ≳ 0.5 s
and fast flavor conversion leads to flavor equipartition, with the spectral energy distribution of
ν
e (ν̅e) and ν
x
(ν̅
x
) becoming comparable. Notably, flavor
equipartition is not a generic outcome of fast flavor conversion, rather it is a consequence of
the relatively similar properties of neutrinos of different flavors characterizing the late
accretion phase. Artificially tweaking the collision term to introduce an electron lepton number
angular crossing for t
pb ≲ 0.5 s, we observe that flavor equipartition is
not achieved. While our findings are restricted to a specific supernova model, and they only take
into account the feedback of the neutrino background on the flavor conversion, they suggest a rich
phenomenology in the supernova core as a function of the post-bounce time which needs to be
further explored to assess its impact on the explosion mechanism.