We study neutrino interactions in a hadron gas within a relativistic
framework. The hadron matter is described by a non-interacting Fermi gas in
beta equilibrium. We show that the introduction of relativistic effects causes
a sizable enhancement of the neutrino-scattering cross sections.Comment: To appear in the proceedings of International School of Nuclear
Physics: 27th Course: "Neutrinos in Cosmology, in Astro, Particle and Nuclear
Physics". Erice, Sicily, Italy, 16-2