Motility-Induced Phase Separation of harmonic Active Ornstein-Uhlenbeck particles fulfilling Detailed Balance

Abstract

Active matter constitutes a class of nonequilibrium systems which has attracted a lot of attention over the past decades, and Motility-Induced Phase Separation (MIPS) lies among one of its most salient collective phenomena. Although MIPS has been studied in depth, the question of whether this active phase transition can only occur in the presence of out-of-equilibrium fluctuations remains open. In this work, we numerically show that harmonic Active Ornstein-Uhlenbeck Particles (AOUP), with an equilibrium dynamics fulfilling detailed balance, undergo MIPS. We studied analytically 2-body interactions, identifying an effective attraction increasing with activity, to show that n-body effects are needed in order to account for the nature of the transition, and in particular, of the dense phase. Finally, a recursive method to obtain a multibody expansion of the partition function for the complete system is developed