Theoretical Models

Extraterrestrial: phase space densities in SW cannot account for MeV electrons, Jovian or not.
Nishida recirculation: Neither efficiency, nor low-L scattering, nor high-L scattering, nor predicted pitch-angle distributions have been observed. (It may work for ions in banana orbits though!)
Substorm energization: Neither frequency of substorms, nor AE nor Bz correlated to MeV e. It’s a hypothesis about energy sources, not data.
Internal source, wave-particle energization. Again, data rarely show negative radial gradients of f. If true, it fails to explain most storms. And waves used to be a loss process...

Extraterrestrial: phase space densities in SW cannot account for MeV electrons, Jovian or not.