Neutrinos in dense media: helicity- and pair correlations

Neutrinos propagating in media (matter and electromagnetic fields) undergo flavor and helicity oscillations, where helicity transitions are induced both by electromagnetic fields and matter currents. In addition, it has been shown that correlations between neutrinos and antineutrinos of opposite momentum can build up in anisotropic media. We discuss the neutrinos' equations of motion in the mean-field approximation for homogeneous yet anisotropic media highlighting previous results on the physical implications and typical orders of magnitude of helicity- and pair correlations.