Local detailed balance for active particle models

Abstract: Starting from a Huxley-type model for an agitated vibrational mode, we propose an embedding of standard active particle models in terms of two-temperature processes. One temperature refers to an ambient thermal bath, and the other temperature effectively describes ``hot spots,'' i.e., systems with few degrees of freedom showing important population homogenization or even inversion of energy levels as a result of activation. That setup admits to quantitatively specifying the resulting nonequilibrium driving, rendering local detailed balance to active particle models, and making easy contact with thermodynamic features. In addition, we observe that the shape transition in the steady low-temperature behaviour of run-and-tumble particles (with the interesting emergence of edge states at high persistence) is stable and occurs for all temperature differences, including close to equilibrium.