Fluctuation theorems and inequalities generalizing the second law of thermodynamics off equilibrium

We present a general framework for systems which are prepared in a non-stationary non-equilibrium state in the absence of any perturbation, and which are then further driven through the application of a time-dependent perturbation. We distinguish two different situations depending on the way the non-equilibrium state is prepared, either it is created by some driving; or it results from a relaxation following some initial non-stationary conditions. Our approach is based on a recent generalization of the Hatano-Sasa relation for non-stationary probability distributions. We also investigate whether a form of second law holds for separate parts of the entropy production, in a way similar to the work of M. Esposito et al., Phys. Rev. Lett., 104:090601 (2010), but for a non-stationary reference process instead of a stationary one. We find that although the special structure of the theorems derived in this reference is not recovered in the general case, detailed fluctuation theorems still hold separately for parts of the entropy production in this case. These detailed fluctuation theorems lead to interesting generalizations of the second-law of thermodynamics off equilibrium.