Decomposition of force fluctuations far from equilibrium.

By studying a nonequilibrium Langevin system, we find that a simple condition determines the decomposition of the coarse-grained force into a dissipative force, an effective driving force and noise. From this condition, we derive a universal inequality, D > or = gamma mu2(d)T , relating the diffusion constant D , the differential mobility mu(d) , the bare friction constant gamma and the temperature T . Due to the general nature of the argument we present, we believe that our idea concerning this decomposition can be applied to a wide class of systems far from equilibrium.