Active polar flock with birth and death

Abstract

We study a collection of self-propelled polar particles on a two-dimensional substrate with birth and death. We introduce a minimal lattice model for the system using active Ising spins, where each particle can have two possible orientations. The activity is modeled as a biased movement of the particle along its direction of orientation. The particles also align with their nearest neighbors using Metropolis Monte Carlo algorithm. The system shows a disorder-to-order transition by tuning the temperature of the system. Additionally, the birth and death of the particles is introduced through a birth and death parameter γ. The system is studied near the disorder-to-order transition. The nature of disorder-to-order transition shows a crossover from the first order, discontinuous to continuous type as we tune γ from zero to finite values. We also write the effective free energy of the local order parameter using perturbative calculation, and it confirms the dependence of the nature of phase transition on the birth and death parameter.