Transient multimodality in relaxation from an unstable state.

We analyse a relaxation process from an unstable state during which transient multimodality occurs. This phenomenon is investigated experimentally on an electronic analogue circuit which mimics an overdamped bistable oscillator described by a sixth--order polynomial U(x) and is driven by a Gaussian white noise. The measured times and positions at which new maxima appear in the probability distribution function agree well with the theoretical predictions. It is shown that the shape of the potential guarantees the existence of two different time scales, allowing for the coexistence of three probability distribution peaks during a sizeable interval of time, even though there is no long "flat" region in the potential where U'(x) is very small. Finally, the concept of marginality with reference to unsteady states is discussed