Uncovering novel phase transitions in dense dry polar active fluids using a lattice Boltzmann method

The dynamics of dry active matter have implications for a diverse collection of biological phenomena spanning a range of length and time scales, such as animal flocking, cell tissue dynamics, and swarming of inserts and bacteria. Uniting these systems are a common set of symmetries and conservation laws, defining dry active fluids as a class of physical system. Many interesting behaviours have been observed at high densities, which remain difficult to simulate due to the computational demand. Here, we show how two-dimensional dry active fluids in a dense regime can be studied using a simple modification of the lattice Boltzmann method. We apply our method on a model that exhibits motility-induced phase separation, and an active model with contact inhibition of locomotion, which has relevance to collective cell migration. For the latter, we uncover multiple novel phase transitions: two first-order and one potentially critical. We further support our simulation results with an analytical treatment of the hydrodynamic equations obtained via a Chapman-Enskog coarse-graining procedure.

Automated summary

The dynamics of dry active matter have important implications for a range of biological phenomena, including animal flocking, cell tissue dynamics, and swarming of insects and bacteria. Many interesting behaviors have been observed at high densities, but remain difficult to simulate due to computational demand. By modifying the lattice Boltzmann method, researchers were able to study two-dimensional dry active fluids in a dense regime, uncovering multiple novel phase transitions and supporting simulation results with analytical treatment of hydrodynamic equations.