Anomalous velocity distributions in active Brownian suspensions

Large scale simulations and analytical theory have been combined to obtain the non-equilibrium velocity distribution, $f(v)$, of randomly accelerated particles in suspension. The simulations are based on an event-driven algorithm, generalized to include friction. They reveal strongly anomalous but largely universal distributions which are independent of volume fraction and collision processes. Consequently, a one-particle model can capture all the essential features of $f(v)$. We have solved the one particle model analytically in the limit of strong damping, where we find a divergence of $f(v)$ for small argument, a $1/v$-decay for intermediate and a Gaussian decay for the largest velocities. Many particle simulations and solution of the one-particle model agree for all values of the damping.