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Condensed Matter > Statistical Mechanics
Title: Direction reversing active Brownian particle in a harmonic potential
(Submitted on 27 Jul 2021 (v1), last revised 13 Sep 2022 (this version, v2))
Abstract: We study the two-dimensional motion of an active Brownian particle of speed $v_0$, with intermittent directional reversals in the presence of a harmonic trap of strength $\mu$. The presence of the trap ensures that the position of the particle eventually reaches a steady state where it is bounded within a circular region of radius $v_0/\mu$, centered at the minimum of the trap. Due to the interplay between the rotational diffusion constant $D_R$, reversal rate $\gamma$, and the trap strength $\mu$, the steady state distribution shows four different types of shapes, which we refer to as active-I & II, and passive-I & II phases. In the active-I phase, the weight of the distribution is concentrated along an annular region close to the circular boundary, whereas in active-II, an additional central diverging peak appears giving rise to a Mexican hat-like shape of the distribution. The passive-I is marked by a single Boltzmann-like centrally peaked distribution in the large $D_R$ limit. On the other hand, while the passive-II phase also shows a single central peak, it is distinguished from passive-I by a non-Boltzmann like divergence near the origin. We characterize these phases by calculating the exact analytical forms of the distributions in various limiting cases. In particular, we show that for $D_R\ll\gamma$, the shape transition of the two-dimensional position distribution from active-II to passive-II occurs at $\mu=\gamma$. We compliment these analytical results with numerical simulations beyond the limiting cases and obtain a qualitative phase diagram in the $(D_R,\gamma,\mu^{-1})$ space.
Submission history
From: Ion Santra [view email][v1] Tue, 27 Jul 2021 07:32:32 GMT (1987kb,D)
[v2] Tue, 13 Sep 2022 17:08:37 GMT (1987kb,D)
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