# Relativistic at freeze out? Definition of HDM

by cohen990
Tags: definition, freeze, relativistic
 P: 7 Okay so in a HDM scenario, I have seen it described that the neutrinos were relativistic at freeze out. (If I could find it I would reference it.) Is this a contradictory statement? The condition for relativistic travel is E>>m but just before freezeout, the neutrino has energy equal to the thermal energy of the universe (as it is in thermal equilibrium). Since the particle freezes out when the energy of the universe $\approx$ the mass of the particle, then just before freeze out the particle is not relativistic! Correct? Anyway, thanks for your time, Dan
 Quote by cohen990 Okay so in a HDM scenario, I have seen it described that the neutrinos were relativistic at freeze out. (If I could find it I would reference it.) Is this a contradictory statement? The condition for relativistic travel is E>>m but just before freezeout, the neutrino has energy equal to the thermal energy of the universe (as it is in thermal equilibrium). Since the particle freezes out when the energy of the universe $\approx$ the mass of the particle, then just before freeze out the particle is not relativistic! Correct? Anyway, thanks for your time, Dan