Disordered boundaries destroy bulk phase separation in scalar active matter

TL;DR

Disordered boundaries in scalar active matter systems prevent bulk phase separation in dimensions less than three, contrasting with equilibrium systems, due to long-range correlations and eddy formations that disrupt phase separation.

Contribution

This work reveals how disordered boundaries inhibit phase separation in active matter, a phenomenon not observed in equilibrium systems, through theoretical analysis and numerical validation.

Findings

Disordered boundaries destroy bulk phase separation in scalar active systems in dimensions less than three.

Long-ranged density correlations and eddy cascades prevent phase separation.

Results hold for dilute and interacting systems with a unique hydrodynamic mode.

Abstract

We show that disordered boundaries destroy bulk phase separation in scalar active systems in dimension $d<d_c=3$. This is in strong contrast with the equilibrium case where boundaries have no impact on the bulk of phase-separated systems. The underlying mechanism is revealed by considering a localized deformation of an otherwise flat wall, from which the case of a disordered boundary can be inferred. We find long-ranged correlations of the density field as well as a cascade of eddies which we show prevent bulk phase separation in low enough dimensions. The results are derived for dilute systems as well as in the presence of interactions, under the sole condition that the density field is the unique hydrodynamic mode. Our theoretical calculations are validated by numerical simulations of microscopic active systems.