Constraints on Spatial Variations in the Fine-Structure constant from Planck

Understand

We use the Cosmic Microwave Background (CMB) anisotropy data from Planck to constrain the spatial fluctuations of the fine-structure constant \alpha.

• Through Thompson scattering of CMB photons, spatial anisotropies of \alpha lead to higher-order correlations in the CMB anisotropies.
• We use a quadratic estimator based on the four-point correlation function of the CMB temperature anisotropy to extract the angular power spectrum of the spatial variation of the fine-structure constant projected along the line of sight at the last scattering surface.
• At tens of degree angular scales and above, we constrain the rms fluctuations of the fine structure constant to be \delta \alpha/\alpha_0= (1.34 +/- 5.82) x 10^-2 at the 95% confidence level with respect to the standard value \alpha_0.