Critical Motility-Induced Phase Separation in Three Dimensions is Consistent with Ising Universality

Abstract: Numerical investigations aiming to determine the universality class of critical motility-induced phase separation (MIPS) in two dimensions (2D) have resulted in inconclusive findings. Here, using finite-size scaling results obtained from large-scale computer simulations, we find that the static and dynamic critical exponents associated with 3D MIPS all closely match those of the 3D Ising universality class with a conserved scalar order parameter. This finding is corroborated by fluctuating hydrodynamic description of the critical dynamics of the order parameter field which precisely matching model B in three dimensions. Our work suggests that 3D MIPS and indeed the entire phase diagram of active Brownian spheres is remarkably similar to that of molecular passive fluids despite the absence of Boltzmann statistics.