Exact mechanisms of arrested coarsening in active-matter systems

Ascertain the exact physical mechanisms responsible for the suppression or arrest of coarsening in active-matter systems of self-propelled agents, particularly for the travelling polar–nematic density waves described by the hydrodynamic equations for the density c and order parameters ρ1 and ρ2 with Marangoni advection (Eq. (5) coupled with Eq. (4)), by identifying why volume (Ostwald ripening) and translation (coalescence) modes fail to drive continued coarsening.

Background

In two-dimensional simulations, the authors observe that travelling polar–nematic waves broaden and adjust their speed as the Marangoni parameter increases, but the patterns remain stable against coarsening: waves do not merge except transiently after parameter changes. The number of bands decreases only during transients and then remains fixed, indicating arrested coarsening.

They note that suppression or arrest of coarsening is known in driven or active systems through different mechanisms (volume mode vs translation mode). While they suggest that the non-variational nature of the hydrodynamic equations (Eq. (5)) might phenomenologically explain coarsening suppression, they explicitly state that the exact physical mechanisms underpinning arrested coarsening in active-matter systems are still unclear and call for a detailed stability analysis of travelling wave states.