Microscopic theory for hyperuniformity in two-dimensional chiral active fluid

Chiral active matter is one of the important classes of active matter in which each component performs left-right symmetry-broken motions. Two-dimensional chiral active fluids have a striking feature called hyperuniformity, an anomalous suppression of large-scale density fluctuations. This is in stark contrast to other types of active matter, including polar active fluids or active nematics, where large-scale density fluctuations are enhanced. Hyperuniformity in two-dimensional chiral active fluids has been observed both numerically and experimentally. However, a theoretical understanding from a microscopic point of view is still lacking.

Here, we develop a microscopic theory that can explain its mechanism qualitatively. Effective fluctuating hydrodynamic equations are derived from a simple particle model of chiral active matter. The linear analysis of the obtained equations explains hyperuniformity.