Robust laboratory limits on a cosmological spatial gradient in the electromagnetic fine-structure constant from accelerometer experiments

TL;DR

This paper demonstrates that laboratory accelerometer experiments can set stringent limits on spatial variations of the fine-structure constant, improving previous bounds and potentially testing cosmological anisotropies suggested by astrophysical observations.

Contribution

It introduces a novel laboratory approach using accelerometer data to constrain spatial gradients in fundamental constants, surpassing previous clock-based bounds.

Findings

Laboratory data constrain spatial gradient of α to less than 6.6×10⁻⁴ per Gyr at 95% confidence.

Accelerometer experiments outperform clock-based methods in bounding α gradients.

Future improvements could test cosmological α-dipole signals in laboratory settings.

Abstract

Quasar absorption spectral data indicate the presence of a spatial gradient in the electromagnetic fine-structure constant $\alpha$ on cosmological length scales. We point out that experiments with accelerometers, including torsion pendula and atom interferometers, can be used as sensitive probes of cosmological spatial gradients in the fundamental constants of nature, which give rise to equivalence-principle-violating forces on test masses. Using laboratory data from the E\"ot-Wash experiment, we constrain spatial gradients in $\alpha$ along any direction to be $| \boldsymbol{\nabla} \alpha / \alpha | < 6.6 \times 10^{-4}~(\textrm{Glyr})^{-1}$ at $95\%$ confidence level. Our result represents an order of magnitude improvement over laboratory bounds from clock-based searches for a spatial gradient in $\alpha$ directed along the observed cosmological $\alpha$-dipole axis. Improvements to accelerometer experiments in the foreseeable future are expected to provide sufficient sensitivity to test the cosmological $\alpha$-dipole seen in astrophysical data.