  In a previous work [16], a new model was introduced, taking into account the
role of the Fermi weak force due to neutrinos coupled to magnetohydrodynamic
plasmas. The resulting neutrino-magnetohydrodynamics was investigated in a
particular geometry associated with the magnetosonic wave, where the ambient
magnetic field and the wavevector are perpendicular. The corresponding fast,
short wavelength neutrino beam instability was then obtained in the context of
supernova parameters. The present communication generalizes these results,
allowing for arbitrary direction of wave propagation, including fast and slow
magnetohydrodynamic waves and the intermediate cases of oblique angles. The
numerical estimates of the neutrino-plasma instabilities are derived in extreme
astrophysical environments where dense neutrino beams exist.
