Suppression of discontinuous phase transitions by particle diffusion

We investigate the phase transitions of the q-state Brownian Potts model in two dimensions (2D) comprising Potts spins that diffuse like Brownian particles and interact ferromagnetically with other spins within a fixed distance. With extensive Monte Carlo simulations we find a continuous phase transition from a paramagnetic to a ferromagnetic phase even for q > 4. This is in sharp contrast to the existence of a discontinuous phase transition in the equilibrium q-state Potts model in 2D with q > 4. We present detailed numerical evidence for a continuous phase transition and argue that diffusion generated dynamical positional disorder suppresses phase coexistence leading to a continuous transition.