STABILITY OF INCOHERENCE IN AN ISOTROPIC GAS OF OSCILLATING NEUTRINOS- ART. NO. 073002

In the early universe and in supernovae, the flavor evolution of massi ve neutrinos is nonlinear. Previously, numerical simulations have expl ored these conditions and have sometimes found collective, synchronize d neutrino oscillations. Here these coherent phenomena are studied in the simplest possible system, an isotropic gas of two-flavor neutrinos . An analytical method is used to study the stability of the incoheren t state. It is found that the incoherent state has neutral stability. That is, a steady state synchronization can exist for all nonzero neut rino densities, but the amount depends on the initial conditions. This result is verified by numerical simulation, but it is shown that nume rical simulations are accurate for only a limited time. In more compli cated neutrino systems, the incoherent state could be stable or unstab le. [S0556-2821(98)02919-1]