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

## TL;DR

This paper introduces a modified lattice Boltzmann method to simulate dense dry active fluids, revealing new phase transitions and providing analytical insights into their hydrodynamics.

## Contribution

It presents a novel simulation approach for dense dry active matter and uncovers previously unknown phase transitions in these systems.

## Key findings

- Discovered multiple new phase transitions, including two first-order and one potentially critical.
- Validated simulation results with analytical hydrodynamic equations.
- Applied method to models relevant to biological collective behaviors.

## Abstract

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.