  An algebraic approach to the neutrino propagation in dense media is
presented. The Hamiltonian describing a gas of neutrinos interacting with each
other and with background fermions is written in terms of the appropriate SU(N)
operators, where N is the number of neutrino flavors. The evolution of the
resulting many-body problem is formulated as a coherent-state path integral.
Some commonly used approximations are shown to represent the saddle-point
solution of the path integral for the full many-body system.
