Fast flavor conversion in dense neutrino media

The flavor conversion of a neutrino usually occurs on length scales of its vacuum oscillation wavelength. In a dense neutrino medium such as that in a core-collapse supernova or a binary neutron star merger, this flavor conversion can be expedited by the large densities of the ambient matter and/or neutrinos. We explain the origin of this fast flavor conversion phenomenon and why it may be relevant to supernova physics.