Role of External Flow and Frame Invariance in Stochastic Thermodynamics

For configurational changes of soft matter systems affected or caused by external hydrodynamic flow, we identify applied work, exchanged heat, and entropy change on the level of a single trajectory. These expressions guarantee invariance of stochastic thermodynamics under a change of frame of reference. As criterion for equilibrium $\mathit{\text{vs.}}$ nonequilibrium, zero $\mathit{\text{vs.}}$ nonzero applied work replaces detailed balance $\mathit{\text{vs.}}$ nonvanishing currents, since both latter criteria are shown to depend on the frame of reference. Our results are illustrated quantitatively by calculating the large deviation function for the entropy production of a dumbbell in shear flow.