Entropy production along a stochastic trajectory and an integral fluctuation theorem

For stochastic non-equilibrium dynamics like a Langevin equation for a colloidal particle or a master equation for discrete states, entropy production along a single trajectory is studied. It involves both genuine particle entropy and entropy production in the surrounding medium. The integrated sum of both $\Delta s\t$is shown to obey a fluctuation theorem $<\exp[-\Delta s\t]> =1$ for arbitrary initial conditions and arbitrary time-dependent driving over a finite time interval.