Mode Coupling Theory for Nonequilibrium Glassy Dynamics of Thermal Self-Propelled Particles

Abstract

We present a promising mode coupling theory study for the relaxation and glassy dynamics of a system of strongly interacting self-propelled particles, wherein the self-propulsion force is described by Ornstein-Uhlenbeck colored noise and thermal noises are included. Our starting point is an effective Smoluchowski equation governing the distribution function of particle's positions, from which we derive a memory function equation for the time dependence of density fluctuations in nonequilibrium steady states. With the basic assumption of absence of macroscopic currents and standard mode coupling approximation, we can obtain expressions for the irreducible memory function and other relevant dynamic terms. With these equations obtained, we study the glassy dynamics of this thermal self-propelled particles system by investigating the Debye-Waller factor f_{q} and relaxation time \tau_{\alpha} as functions of the persistence time \tau_{p} of self-propulsion, the single particle effective temperature T_{\text{eff}} as well as the number density \rho. Consequently, we find the critical density \rho_{c} for given \tau_{p} shifts to larger values with increasing magnitude of propulsion force or effective temperature, in good accordance with previous reported simulation works. In addition, the theory facilitates us to study the critical effective temperature T_{\text{eff}}^{c} for fixed \rho as well as its dependence on \tau_{p}. We find that T_{\text{eff}}^{c} increases with \tau_{p} and in the limit \tau_{p}\to0, it approaches the value for a simple passive Brownian system as expected. Our theory also well recovers the results for passive systems and can be easily extended to more complex systems such as active-passive mixtures.