Frenetic aspects of second order response

Starting from the second order around thermal equilibrium, the response of a statistical mechanical system to an external stimulus is not only governed by dissipation and depends explicitly on dynamical details of the system. The so called frenetic contribution in the second order around equilibrium is illustrated in different physical examples, such as for non-thermodynamic aspects in the coupling between a system and reservoir, for the dependence on disorder in the dielectric response and for the nonlinear correction to the Sutherland-Einstein relation. More generally, the way in which a system's dynamical activity changes by perturbation is visible (only) from the nonlinear response. A theoretical framework to compute the second order response around equilibrium is provided and the importance of the so called frenetic contribution is illustrated.