Neutrino mass in dense matter

For massless leptons interacting with massive vector bosons in a hot and dense medium the possibility of the generation of an effective mass is investigated. By using the one-loop approximation of the neutrino self-energy in the Weinberg-Salam model in the unitary gauge, expressions are found for the dispersion equations of quasiparticles in the low momentum limit. A negative effective mass can be defined for neutrinos, whereas for holes and antineutrinos this mass is positive.