Intrawell relaxation of overdamped Brownian particles.

We consider an overdamped Brownian particle in a well. When the particle escapes, it does so as an instanton, i.e., in one run and without dwelling anywhere on the way from the bottom of the well to the top of the barrier. For a sufficiently steep slope the instanton time equals the time it takes the particle to deterministically slide down the same slope. We show that the instanton time is also the relaxation time for the escape rate after the barrier changes shape.