Resonant conversions of extremely high energy neutrinos in dark matter halos

We study the effect of adiabatically resonant conversion in galactic halos of neutrinos at the highest energies (similar to 10(20)-10(22) eV), when the nu source is in the center of a galaxy. Using the standard neutrino properties and the standard cosmological scenario for hot dark matter, we find that interesting conversions may take place just for neutrino parameters relevant to the solar and atmospheric neutrino problem. The effect is due to the large enhancement in the nu density in galactic halos and to the form of the effective matter potential both below and above the pole of the Z resonance. [S0556-2821(99)03210-5].