FUGACITY AND REHEATING OF PRIMORDIAL NEUTRINOS.

We clarify in a quantitative way the impact that distinct chemical T_c and kinetic T_k freeze-out temperatures have on the reduction of the neutrino fugacity ϒ_ν below equilibrium, i.e. ϒ_ν<1, and the increase of the neutrino temperature T_ν via partial reheating. We establish the connection between ϒ_ν and T_k via the modified reheating relation T_ν(ϒ_ν)/T_γ, where T_γ is the temperature of the background radiation. Our results demonstrate that one must introduce the chemical nonequilibrium parameter, i.e. the fugacity, ϒ_ν, as an additional standard cosmological model parameter in the evaluation of CMB fluctuations as its value allows measurement of T_k. [ABSTRACT FROM AUTHOR]