From Attraction to Repulsion: Emergent Interactions in Harmonically Coupled Active Binary System

TL;DR

This study explores how two active particles coupled by a harmonic potential exhibit emergent attractive or repulsive interactions depending on activity, coupling, and temperature, revealing novel non-Gaussian fluctuation behaviors.

Contribution

It analytically characterizes the conditions under which effective interactions switch from attraction to repulsion in active particle systems.

Findings

Effective repulsion emerges at low temperatures in certain regimes.

Repulsion is driven by differences in self-propulsion speeds.

Non-Gaussian fluctuations are observed in the centroid distribution.

Abstract

We investigate the emergent interactions between two active Brownian particles coupled by an attractive harmonic potential and in contact with a thermal reservoir. By analyzing the stationary distribution of their separation, we demonstrate that the effective interaction can be either attractive or repulsive, depending on the interplay between activity, coupling strength, and temperature. Notably, we find that an effective short-range repulsion emerges in the strong and moderate-coupling regimes, when the temperature is below some threshold value, which we characterize analytically. In the strong-coupling regime, the repulsion emerges solely due to the difference in the self-propulsion speeds of the particles. We also compute the short-time position distribution of the centroid of the coupled particles, which shows strongly non-Gaussian fluctuations at low temperatures.