Nonlinear neutrino oscillations in the expanding Universe.

interactions with electrons and positrons. A broad spectrum of neutrino and antineutrino behavior is observed, ranging from vacuumlike to smooth. Oscillations exhibiting self-maintained coherence also appear. We identify a variety of neutrino properties arising as a consequence of the nonlinear neutrino self-interactions. The nonlinear effects tend to suppress any CP asymmetry relative to the linear case. An analytical approximation scheme reproducing bulk neutrino behavior is described. We discuss some physical implications of our results.