Constraints on variation of fine structure constant from joint SPT-SZ and XMM-Newton observations

TL;DR

This study uses observations of galaxy clusters to test whether the fine structure constant varies over cosmic time or space, finding no significant variation and thus supporting its constancy.

Contribution

It provides the first constraints on the variation of the fine structure constant using SZ and X-ray cluster data, including limits on both redshift and spatial variations.

Findings

No significant logarithmic variation of alpha with redshift.

No evidence for dipole spatial variation of alpha.

Constraints on alpha variation at about 0.7% level.

Abstract

We search for a variation of the electromagnetic fine structure constant ($\alpha \equiv e^2/\hbar c$) using a sample of 58 SZ selected clusters in the redshift range ($0.2<z<1.5$) detected by the South Pole Telescope, along with X-ray measurements using the XMM-Newton observatory. We use the ratio of the integrated SZ Compto-ionization to its X-ray counterpart as our observable for this search. We first obtain a model-independent constraint on $\alpha$ of about 0.7%, using the fact that the aforementioned ratio is constant as a function of redshift. We then look for a logarithmic dependence of $\alpha$ as a function of redshift: $\Delta \alpha/\alpha = -\gamma \ln(1+z)$, as this is predicted by runaway dilaton models. We find that $\gamma$ = $-0.046 \pm 0.1$, which indicates that there is no logarithmic variation of $\alpha$ as a function of redshift. We also search for a dipole variation of the fine structure constant using the same cluster sample. We do not find any evidence for such a spatial variation.