NEAR-LINEAR REGIME OF GRAVITATIONAL-WAVES IN NUMERICAL RELATIVITY

We report on a systematic study of the dynamics of gravitational waves in full 3D numerical relativity. We find that there exists an interes ting regime in the parameter space of the wave configurations: a near- linear regime in which the amplitude of the wave is low enough that on e expects the geometric deviation from flat spacetime to be negligible , but nevertheless, where nonlinearities can excite unstable modes of the Einstein evolution equations causing the metric functions to evolv e out of control. The implications of this for numerical relativity ar e discussed.