Effective attraction by repulsion

TL;DR

This paper investigates how repulsive active particles can exhibit effective attraction through a microscopic theory, revealing that attraction emerges as a higher-order effect in a minimal model.

Contribution

It provides an exact microscopic analysis showing the emergence of effective attraction as a higher-order effect in repulsive active particles.

Findings

Effective attraction arises as a higher-order contribution in the pair potential.

Repulsive particles initially behave as effectively repulsive at leading order.

The study uses a minimal model of two soft run-and-tumble particles.

Abstract

Repulsive self-propelled particles tend to cluster, leading to Motility-Induced Phase Separation (MIPS). By analogy with equilibrium phase separation, the onset of MIPS has been associated with a transition to effective attraction between particles. Using an exact microscopic theory, we quantify the emergence of effective attraction in a minimal model: two soft run-and-tumble particles in a periodic domain. We show that, as repulsion increases, the leading-order behaviour is that of effective repulsion, while effective attraction emerges as a higher-order contribution to the renormalisation of the pair potential.