The Fine Structure Constant and the CMB Damping Scale

TL;DR

Recent CMB measurements suggest possible variations in the fine structure constant and effective relativistic degrees of freedom, indicating potential new physics beyond the standard cosmological model.

Contribution

This study provides new constraints on the variation of the fine structure constant using recent CMB data, highlighting degeneracies with Neff and implications for unknown physics.

Findings

Constraints on alpha are tightened to 0.984 ± 0.005.

Data indicates a deviation from the standard alpha value at over two sigma.

Degeneracy between alpha variations and Neff affects parameter constraints.

Abstract

The recent measurements of the Cosmic Microwave Background anisotropies at arcminute angular scales performed by the ACT and SPT experiments are probing the damping regime of CMB fluctuations. The analysis of these datasets unexpectedly suggests that the effective number of relativistic degrees of freedom is larger than the standard value of Neff = 3.04, and inconsistent with it at more than two standard deviations. In this paper we study the role of a mechanism that could affect the shape of the CMB angular fluctuations at those scales, namely a change in the recombination process through variations in the fine structure constant. We show that the new CMB data significantly improve the previous constraints on variations of {\alpha}, with {\alpha}/{\alpha}0 = 0.984 \pm 0.005, i.e. hinting also to a more than two standard deviation from the current, local, value {\alpha}0. A significant degeneracy is present between {\alpha} and Neff, and when variations in the latter are allowed the constraints on {\alpha} are relaxed and again consistent with the standard value. Deviations of either parameter from their standard values would imply the presence of new, currently unknown physics.