A new method of calculating very small cross sections

Langevin equations are used to model many processes of physical interest, including low-energy nuclear collisions. We develop a general method for computing probabilities of very rare events (e.g. small fusion cross-sections) for processes described by Langevin dynamics. As we demonstrate with numerical examples, our method can converge to the desired answer at a rate which is orders of magnitude faster than that achieved by using direct simulations of the process in question. (author)