Entropy Productions and Fluctuation Theorems: A Unifying Change-of-Probability-Measure Formalism.

In terms of change of probability measure (CPM) we examine the origin of various entropy productions (EPs) of general stochastic processes and the domain of validity of their fluctuation theorems. EPs in physics and chemistry are introduced by considering a reversal of a process. We use a two-time-step, finite-state-space, time-homogeneous Markov chain to illustrate the difference between time reversal and protocol reversal, and their corresponding CPMs. Six distinct EPs arise from the two reversals. Their relations and corresponding fluctuation theorems are presented.