Do the highest-energy merger neutrinos reach the zero-field opacity regime at ultra-strong B?

Determine whether the highest-energy neutrinos produced in binary neutron star mergers lie in the large-neutrino-energy regime in which neutrino absorption opacities in ultra-strong magnetic fields (on the order of 5×10^16–10^17 G) approach their zero-magnetic-field values with only small corrections.

Background

In ultra-strong magnetic fields, Landau quantization modifies charged-particle states and can strongly affect neutrino absorption opacities, especially at low to moderate neutrino energies where resonances and magnetic-moment effects are important. Earlier studies indicate that in the asymptotic large-neutrino-energy limit, these opacities should approach their zero-field values with small corrections.

The analysis here examines stronger magnetic fields (≈5×1016–1017 G) and conditions relevant to neutron star merger ejecta. While prior work suggests a return to zero-field behavior at sufficiently large neutrino energy, it remains unclear whether the highest-energy neutrinos generated in mergers actually reach this regime under such strong fields.

References

The results of Refs. indicate that at large neutrino energy, the opacities should approach the value with zero field with small corrections. Whether the highest energy neutrinos from a neutron star merger are in this regime for such strong fields is unclear.

— Effects of Landau quantization on neutrino emission and absorption (2412.02925 - Kumamoto et al., 4 Dec 2024) in Section 4.1 (Low density conditions)