Modeling the nonlinear dielectric response of glass formers.

The recently developed pragmatical model of asymmetric double-well potentials with a finite lifetime is applied to nonlinear dielectric data in polar undercooled liquids. The viscous effects from the finite lifetime provide a crossover from the cooperative jumps of many molecules at short times to the motion of statistically independent molecules at long times. The model allows us to determine the size of cooperatively rearranging regions from nonlinear ω-data and throws new light on a known inconsistency between nonlinear ω and 3ω-signals for glycerol and propylene carbonate.