Elements of a unified framework for response formulae

We provide a physical interpretation of the first and second order terms occurring in Ruelle response formalism. We show that entropy fluxes play a major role in determining the response of the system to perturbations. Along this line, we show that our framework allows one to recover a wealth of previous results of response theory in both deterministic and stochastic contexts. In particular, we are able to shed light on the crosslinks between the dynamical systems approach la Ruelle and large deviations methods.