Stochastic path power and the Laplace transform

S P Fitzgerald, T J W Honour

Published 2023-12-21Version 1

Transition probabilities for stochastic systems can be expressed in terms of a functional integral over paths taken by the system. Evaluating the integral by the saddle point method in the weak-noise limit leads to a remarkable mapping between dominant stochastic paths and conservative, Hamiltonian mechanics in an effective potential. The conserved ``energy'' in the effective system has dimensions of power. We show that this power, H, can be identified with the Laplace parameter of the time-transformed dynamics. This identification leads to insights into the non-equilibrium behaviour of the system. Moreover, it facilitates the explicit summation over families of trajectories, which is far harder in the time domain. This is crucial for making contact with the long-time equilibrium limit.