Drift, Drag and Brownian motion in the Davies-Unruh bath

TL;DR

This paper explores how particles undergo anisotropic Brownian motion in the Unruh thermal bath, revealing direction-dependent frictional forces caused by quantum correlations, despite the isotropic thermal spectrum observed by accelerated observers.

Contribution

It demonstrates that thermal fluctuations in the Unruh bath are anisotropic and links this anisotropy to quantum correlations affecting particle dynamics.

Findings

Thermal fluctuations are anisotropic in the Unruh bath.

Frictional drag depends on the direction of particle drift.

Quantum correlations influence fluctuation anisotropy.

Abstract

An interesting feature of the Davies-Unruh effect is that an uniformly accelerated observer sees an isotropic thermal spectrum of particles even though there is a preferred direction in this context, determined by the direction of the acceleration g. We investigate the thermal fluctuations in the Unruh bath by studying the Brownian motion of particles in the bath, especially as regards to isotropy. We find that the thermal fluctuations are anisotropic and induce different frictional drag forces on the Brownian particle depending on whether it has a drift velocity along the direction of acceleration g or in a direction transverse to it. Using the fluctuation-dissipation theorem, we argue that this anisotropy arises due to quantum correlations in the fluctuations at large correlation time scales.