New constraints on variations of the fine structure constant from CMB anisotropies

We demonstrate that recent measurements of cosmic microwave background temperature and polarization anisotropy made by the ACBAR, QUAD, and BICEP experiments substantially improve the cosmological constraints on possible variations of the fine structure constant in the early universe. This data, combined with the five year observations from the WMAP mission, yield the constraint alpha/alpha(0) = 0 0.987 +/- 0.012 at 68% C.L. The inclusion of the new Hubble Space Telescope constraints on the Hubble constant further increases the accuracy to alpha/alpha(0) = 1.001 +/- 0.007 at 68% C.L., bringing possible deviations from the current value below the 1% level and improving previous constraints by a factor of similar to 3.