Constraints on Spatial Variations in the Fine-structure Constant from Planck

Abstract

We use the cosmic microwave background (CMB) anisotropy data from Planck to constrain the spatial fluctuations of the fine-structure constant α at a redshift of 1100. We use a quadratic estimator to measure the four-point correlation function of the CMB temperature anisotropies and extract the angular power spectrum fine-structure constant spatial variations projected along the line of sight at the last scattering surface. At tens of degree angular scales and above, we constrain the fractional rms fluctuations of the fine-structure constant to be (δα/α)_rms < 3.4 × 10^-3 at the 68% confidence level. We find no evidence for a spatially varying α at a redshift of 10³.