Simple fluid with broken time reversal invariance

TL;DR

This paper investigates a simple, energy-conserving fluid model with broken time reversal symmetry, revealing long-range velocity correlations and comparing simulation results with theoretical predictions.

Contribution

It introduces a novel collision rule that breaks time reversal symmetry in a hard sphere system and analyzes its effects on stationary states.

Findings

Velocities exhibit long-range correlations decaying as 1/r^d.

Stationary state remains isotropic and homogeneous despite broken time reversal.

Simulation results align qualitatively with theoretical predictions.

Abstract

We characterize a system of hard spheres with a simple collision rule that breaks time reversal symmetry, but conserves energy. The collisions lead to an a-chiral, isotropic, and homogeneous stationary state, whose properties are determined in simulations and compared to an approximate theory originally developed for elastic hard spheres. In the nonequilibrium fluid state, velocities are correlated, a phenomenon known from other nonequilibrium stationary states. The correlations are long-ranged decaying like $1/r^d$ in $d$ dimensions. Such correlations are expected on general grounds far from equilibrium and had previously been observed in driven or non-stationary systems.