Blackbody friction force on a relativistic small neutral particle

TL;DR

This paper calculates the relativistic blackbody friction force on a small neutral particle, revealing differences between frames and the impact of radiation interactions, with implications for ultrarelativistic particles and atomic behavior.

Contribution

It introduces a detailed relativistic framework for blackbody friction on neutral particles, accounting for frame-dependent forces and radiation effects, including atomic linewidth broadening.

Findings

Friction force differs between the particle rest frame and the blackbody frame.

In the ultrarelativistic limit, the friction force diverges as (1-β)^{-3}.

The particle's temperature scales as (1-β)^{-3/8} times the blackbody temperature.

Abstract

The friction force acting on a small neutral particle during relativistic motion relative to the blackbody radiation is calculated in the framework of fluctuation electrodynamics. It is shown that the particle acceleration is determined by the friction force in the particle rest reference frame ($K^{\prime}$-frame) which in general is not equal to the friction force in the frame of the blackbody radiation ($K$-frame). The difference between the friction forces in the different frames is connected with the change of the rest mass of a particle due to the absorption and emission of radiation. The friction force in the $K^{\prime}$-frame is determined only by the interaction of a particle with the blackbody radiation. In the $K$-frame the interaction of a particle with its own thermal radiation also contributes to the friction force. For the steady state temperature of a particle the friction forces in the $K^{\prime}$-and $K$-frames are equal. For an atom the blackbody friction is determined by the electronic linewidth broadening which is calculated considering the interaction of an atom with its own radiation. In the ultrarelativistic case ($1-\beta\rightarrow 0$) for an atom the friction force diverges as $(1-\beta)^{-3}$ and the (average) temperature of an atom $T_2\approx (1-\beta)^{-3/8}T_1$, where $T_1$ is the temperature of the blackbody radiation and $\beta=V/c$. Controversies in the theory of the blackbody friction are discussed.