Long time position distribution of an active Brownian particle in two dimensions

Urna Basu; Satya N. Majumdar; Alberto Rosso; Gregory Schehr

doi:10.1103/PhysRevE.100.062116

paper

Long time position distribution of an active Brownian particle in two dimensions

arXiv:1908.10624 · doi:10.1103/PhysRevE.100.062116

Abstract

We study the late time dynamics of a single active Brownian particle in two dimensions with speed $v_{0}$ and rotation diffusion constant $D_{R}$ . We show that at late times $t ≫ D_{R}^{- 1}$ , while the position probability distribution $P (x, y, t)$ in the $x$ - $y$ plane approaches a Gaussian form near its peak describing the typical diffusive fluctuations, it has non-Gaussian tails describing atypical rare fluctuations when $x^{2} + y^{2} \sim v_{0} t$ . In this regime, the distribution admits a large deviation form, $P (x, y, t) \sim exp [- t D_{R} Φ (x^{2} + y^{2} / (v_{0} t))]$ , where we compute the rate function $Φ (z)$ analytically and also numerically using an importance sampling method. We show that the rate function $Φ (z)$ , encoding the rare fluctuations, still carries the trace of activity even at late times. Another way of detecting activity at late times is to subject the active particle to an external harmonic potential. In this case we show that the stationary distribution $P_{stat} (x, y)$ depends explicitly on the activity parameter $D_{R}^{- 1}$ and undergoes a crossover, as $D_{R}$ increases, from a ring shape in the strongly active limit ( $D_{R} \to 0$ ) to a Gaussian shape in the strongly passive limit $(D_{R} \to \infty)$ .

arXiv comment16 pages, 7 figures. References added and typos corrected. arXiv admin note: text overlap with arXiv:1804.09027

Long time position distribution of an active Brownian particle in two dimensions

Abstract

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