Establish the treatment of collective neutrino oscillations in supernovae

Establish a reliable treatment of collective neutrino oscillations induced by neutrino self-interactions in supernovae to determine their impact on the diffuse supernova neutrino background and the resulting axion constraint.

Background

The diffuse supernova neutrino background prediction depends on flavor conversion between electron antineutrinos and non-electron antineutrinos. The paper parameterizes this conversion through a survival probability, adopting P=1 because collective oscillations generated by neutrino self-interactions are highly uncertain. Although an alternative study finds that extreme oscillation assumptions can reduce the predicted DSNB flux by several tens of percent, the authors state that the treatment of collective oscillations in supernovae remains under debate. Resolving this issue is therefore necessary for a more robust assessment of the DSNB-based axion-proton coupling constraint.

References

This suggests that our limit is conservative in terms of oscillations. Still, the treatment of the collective oscillations in supernovae should be established to discuss the impact on DSNB, although it is still under debate.

— An axion constraint from the diffuse supernova neutrino background indicated by Super-Kamiokande  (2608.17681 - Mori et al., 18 Aug 2026) in Section Discussion, paragraph beginning “So far, we have not considered the effect of neutrino oscillations.”

Second, a fully nonlinear analysis -- going beyond linear stability to understand whether unstable modes saturate, and at what amplitude -- remains an important open problem.

— Stability of Collective Neutrino Oscillations -- A Distributional Approach  (2609.04441 - Majumder et al., 3 Sep 2026) in Section Discussion, paragraph beginning “Several extensions are worth pursuing.”