Anomalous Fluctuations in Fluid Phase of Active Brownian Particles

In this chapter, we study density fluctuations, or particle number fluctuations, and their relation to spatial velocity correlations in disordered homogeneous states of active Brownian particles (ABP). Fluid states of ABP are known to exhibit spatial velocity correlations. Since the longitudinal component of the velocity field is directly coupled to density fluctuations, one naturally expects the density field to also develop spatial correlations, giving rise to giant number fluctuations (GNF). Here, we perform extensive numerical simulations of two-dimensional ABP to verify this scenario.