Physics
Active Brownian Particles (ABPs) self-propel at speed v₀ in direction θ, which undergoes rotational diffusion with rate D_r. Unlike equilibrium systems, ABPs can phase-separate without attractive interactions: fast particles pile up (MIPS — motility-induced phase separation). The persistence length ℓ = v₀/D_r governs clustering.
Controls
Key Concepts
• Persistence length ℓ = v₀/D_r
• MIPS threshold: Pe = v₀/(2R·D_r) > ~40
• Dense phase coexists with dilute gas
• No equilibrium analogue — entropy production is nonzero