  We study the properties of an electromagnetically interacting medium in the
presence of high concentration of electrons at extremely high temperatures and
chemical potentials. We show that the electromagnetic properties of a medium
such as the electric permittivity, magnetic permeability, magnetic moments and
the propagation speed of electromagnetic waves as well as the corresponding
particle processes depend on temperature and density of the medium.
Electromagnetic properties of neutrinos are significantly modified due to their
interactions with electrons when they propagate through such a medium of hot
and dense electrons.
