Emergent Rotational Order and Re-entrant Global Order of Vicsek Agents in a Complex Noise Environment

Abstract: Noisy pursuit in complex environments drives emergent collective behaviors in active matter systems. A compelling platform to study the impact of environment cues is provided by the standard Vicsek model for studying flocking and swarming phenomena. In this study, we explore the collective dynamics of Vicsek agents in a complex noise environment, featuring a noiseless circular region ($\eta_{\text{c}} = 0.0$) surrounded by a noisy outer region ($\eta_{\text{b}} = 1.0$, tunable), with a mutually repelling interactions. By varying the outer noise intensity, we observe an emergent rotational order ($\phi_r$) that peaks at higher noise levels ($\eta_{\text{b}}\sim 1$), as revealed by phase and susceptibility plots. Global order follows ($\phi$) follows a `U' shaped curve, $\phi \sim 0.965$ at $\eta_b=0$, dies down to $\phi \sim 0.57$ at $\eta_b=0.9$ and re-enters at $\eta_b > 1$ and peaks $\phi \sim 0.960$ at $\eta_b=1.5$. The latter rise attributing to $\phi_r$ increase. Higher particle velocities enhance escape rates ($\kappa$) from the circular region, with slower-moving agents exhibiting greater virtual confinement. We quantify escape dynamics through time-averaged and first-passage escape rates, demonstrating velocity-dependent retention on the probability of finding the bi-motility agent flocks at a give time resulting in segregation and trapping. Introducing a gradual noise increase from the circle's center to the outer region reduces both global ($\phi$) and rotational ($\phi_r$) order, underscoring the impact of environmental heterogeneity and sudden annealing over gradual change. These findings offer insights into predicting and manipulating active agent dynamics in heterogeneous environments, with applications in biological and synthetic swarming systems.