Flocking without Alignment Interactions in Attractive Active Brownian Particles

Area of Science:

• Physics
• Statistical Mechanics
• Soft Matter

Background:

• Collective phenomena like flocking are often attributed to alignment interactions.
• Active Brownian particles (ABPs) are a key model for studying self-propelled entities.

Purpose of the Study:

• To investigate flocking behavior in a simple model of attractive ABPs.
• To challenge the necessity of alignment interactions for flocking.
• To identify the transition mechanism from disordered to flocking states.

Main Methods:

• Simulation of a simple model of attractive active Brownian particles.
• Monitoring velocity polarization as an order parameter.
• Analysis of the spatial connected correlation function of particle velocities.

Main Results:

• Flocking behavior observed in ABPs with only attractive, nonaligning interactions.
• A first-order phase transition identified from a disordered state (small clusters) to a flocking state (single emergent flock).
• Scale-free velocity correlations in flocking states and exponential-like decay in nonflocking states.

Conclusions:

• Alignment interactions are not essential for flocking in active matter systems.
• Attractive forces alone can drive collective flocking behavior.
• The findings provide a new perspective on the fundamental mechanisms of self-organized collective motion.