Probing Minicharged Particles with Tests of Coulomb's Law

TL;DR

The paper analyzes minicharged particles (MCPs) as hidden-sector states that modify electromagnetic interactions through vacuum polarization. It shows that MCPs induce a Uehling-type correction to the Coulomb potential, enabling tests of Coulomb's law to probe such particles in laboratory settings. By relating the potential deviation $\delta V(r)$ to the MCP charge $\epsilon$ and mass $m$, the work derives laboratory bounds in the sub-eV to $\mu$eV mass range. For $m \lesssim 0.1~\mu{\rm eV}$, the bound is $\epsilon \lesssim 5 \times 10^{-7}$, making these Cavendish-based tests among the strongest model-independent constraints in this mass window. The study highlights the potential for redoing Cavendish experiments with modern techniques to further tighten these limits and explore hidden-sector physics.

Abstract

Minicharged particles arise in many extensions of the Standard Model. Their contribution to the vacuum polarization modifies Coulomb's law via the Uehling potential. In this note we argue that tests for electromagnetic fifth forces can therefore be a sensitive probe of minicharged particles. In the low mass range <~micro-eV existing constraints from Cavendish type experiments provide the best model-independent bounds on minicharged particles.

Figures (1)

• Figure 1: Laboratory bounds on minicharged particles. The black line (on the left, bottom solid) corresponds to the exclusion limit obtained in this note from the Cavendish type tests of Coulomb's law. The blue bound (on the left, middle solid) arises from constraints on energy losses in high quality accelerator cavities Gies:2006hv. The dark green curve (on the left, top solid) gives the limit arising from bounds on the invisible decay on orthopositronium Badertscher:2006fmRingwald (a similar bound can be obtained from a reactor experiment Gninenko:2006fi). The red-black dashed line denotes the limit Ahlers:2007rdAhlers:2007qf arising from light-shining-through-a-wall experiments Cameron:1993mrEhret:2007cm and applies only to minicharged particles arising from kinetic mixing$^3$ whereas the red dashed curve gives a limit Gies:2006caAhlers:2007qf from polarization experiments Cameron:1993mrZavattini:2007ee$^{4}$ and applies for a pure minicharged particle scenario. The shaded areas are excluded in both scenarios.