In contrast with systems driven by an external field, energy dissipation in active matter is local and independent for each particle. This leads to new dynamics and phases, such as clustering with purely repulsive interactions and collective directed motion. While these phenomena have been studied extensively, understanding how the local dissipation affects the collective dynamics, and its connection with entropy production [1, 2], has remained an elusive goal.

Based on methods of large deviations, we explore how tuning the dissipation, as an independent parameter, modifies the emerging collective behavior. This amounts to a change of ensemble where individual trajectories are biased in terms of their dissipation. By deriving an auxiliary dynamics which effectively realizes the dissipation bias, we put forward a microscopic mechanism which promotes clustering at low dissipation [3]. Moreover, the direct sampling of the biased ensemble reveals the emergence of a collective moving state at high dissipation, despite the absence of aligning interactions [4]. We combine heuristic and analytic arguments to rationalize the dynamical phase transitions between these states.

Overall, our results shed a new light on the control of collective properties by local dissipation. They open the door to the search of new phases and dynamics, as well as unexpected transitions between them, in biased ensembles of active matter.

[1] ÉF, C. Nardini, M. E. Cates, J. Tailleur, P. Visco, and F. van Wijland, 'How far from equilibrium is active matter?', Phys. Rev. Lett. 117, 038103 (2016)
[2] C. Nardini, ÉF, E. Tjhung, F. van Wijland, J. Tailleur, and M. E. Cates, 'Entropy production in field theories without time-reversal symmetry: Quantifying the non-equilibrium character of active matter', Phys. Rev. X 7, 021007 (2017)
[3] ÉF, T. Nemoto, and S. Vaikuntanathan, 'Collisional efficiency controls transport and clustering in active fluids', in preparation
[4] T. Nemoto, ÉF, M. E. Cates, R. L. Jack, and J. Tailleur, 'Optimizing active work: dynamical phase transitions, collective motion and jamming', arXiv:1805.02887