When are active Brownian particles and run-and-tumble particles equivalent? Consequences for motility-induced phase separation

M. E. Cates*, J. Tailleur

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Active Brownian particles (ABPs, such as self-phoretic colloids) swim at fixed speed v along a body-axis u that rotates by slow angular diffusion. Run-and-tumble particles (RTPs, such as motile bacteria) swim with constant u until a random tumble event suddenly decorrelates the orientation. We show that when the motility parameters depend on density rho but not on u, the coarse-grained fluctuating hydrodynamics of interacting ABPs and RTPs can be mapped onto each other and are thus strictly equivalent. In both cases, a steeply enough decreasing v(rho) causes phase separation in dimensions d=2, 3, even when no attractive forces act between the particles. This points to a generic role for motility-induced phase separation in active matter. However, we show that the ABP/RTP equivalence does not automatically extend to the more general case of u-dependent motilities. Copyright (C) EPLA, 2013

Original languageEnglish
Article number20010
Number of pages6
JournalEurophysics Letters
Issue number2
Publication statusPublished - Jan 2013



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