Recent advances in nonequilibrium statistical mechanics shed new light on the ratchet effect. The ratchet motion can thus be understood in terms of symmetry (breaking) considerations. We introduce an additional symmetry operation besides time reversal, that switches between two modes of operation. That mode reversal combined with time reversal decomposes the nonequilibrium action so as to clarify under what circumstances the ratchet current is a second order effect around equilibrium, what is the direction of the ratchet current, and what are possibly the symmetries in its fluctuations.

• Received 17 October 2006

DOI:https://doi.org/10.1103/PhysRevE.76.051117