On anisotropy of the maximum attainable speed of low-mass particles

TL;DR

This paper investigates how the maximum attainable speed of low-mass particles varies with direction, showing that anisotropy effects are extremely small and consistent with experimental limits on photon mass.

Contribution

It provides a detailed analysis of anisotropy in particle speed and its implications for photon mass constraints, improving previous bounds significantly.

Findings

Anisotropy of the one-way speed of light is less than 10^{-37}.

Photon mass constraints are consistent with experimental limits.

Directional variation affects emission patterns at high Lorentz factors.

Abstract

We evaluated the emission of a low-mass particle in the system (atomic) transition for the case when the particle Lorentz factor is $10^{18}$ and found that the angular distribution of emission in the laboratory inertial system is strongly affected by the directional variation of the maximum attainable speed of the particle. We show that for a photon mass consistent with the experimental limit, $m_{ph} \leq 10^{-18}$ eV, due to the experimentally known absence of a significant anisotropy of the photon emission by an atom, the anisotropy of the one-way speed of light, $\Delta c_1/c$, is $10^{-37}$ or less. This is many orders of magnitude smaller than previously reported and the limit becomes even stronger for the lower mass of the photon.