Nonequilibrium steady state of a stochastic system driven by a nonlinear drift force.

We investigate the properties of the nonequilibrium steady state for the stochastic system driven by a nonlinear drift force and influenced by noises that are not identically and independently distributed. The nonequilibrium steady state (NESS) current results from a residual part of the drift force that is not canceled by the diffusive action of noises. From our previous study for the linear drift force, the NESS current was found to circulate on the equiprobability surface with the maximum at a stable fixed point of the drift force. For the nonlinear drift force, we use the perturbation theory with respect to the cubic and quartic coefficients of the drift force. We find an interesting potential landscape picture where the probability maximum shifts from the fixed point of the drift force and, furthermore, the NESS current has a nontrivial circulation that flows off the equiprobability surface and has various centers not located at the probability maximum. The theoretical result is well confirmed by the computer simulation.