Updated constraints on spatial variations of the fine-structure constant

TL;DR

This paper refines constraints on spatial variations of the fine-structure constant using combined archival and dedicated measurements, confirming a dipolar pattern with a smaller amplitude and improved directional constraints.

Contribution

It provides updated limits on the amplitude and direction of a potential dipolar variation of alpha, incorporating newer, more precise measurements to improve previous constraints.

Findings

Dipolar variation remains a good fit to the data.

Amplitude of the dipole is constrained to 8.1±1.7 ppm.

Data cannot distinguish between pure dipole and redshift-dependent models.

Abstract

Recent work by Webb {\it et al.} has provided indications of spatial variations of the fine-structure constant, $\alpha$, at a level of a few parts per million. Using a dataset of 293 archival measurements, they further show that a dipole provides a statistically good fit to the data, a result subsequently confirmed by other authors. Here we show that a more recent dataset of dedicated measurements further constrains these variations: although there are only 10 such measurements, their uncertainties are considerably smaller. We find that a dipolar variation is still a good fit to the combined dataset, but the amplitude of such a dipole must be somewhat smaller: $8.1\pm1.7$ ppm for the full dataset, versus $9.4\pm2.2$ ppm for the Webb {\it et al.} data alone, both at the $68.3\%$ confidence level. Constraints on the direction on the sky of such a dipole are also significantly improved. On the other hand the data can't yet discriminate between a pure spatial dipole and one with an additional redshift dependence.