Future constraints on variations of the fine structure constant from combined CMB and weak lensing measurements

We forecast the ability of future cosmic microwave background and galaxy lensing surveys to constrain variations of the fine structure constant. We found that lensing data, as those expected from satellite experiments as Euclid could improve the constraint from future cosmic microwave background experiments leading to a Delta alpha/alpha = 8 x 10(-4) accuracy. A variation of the fine structure constant alpha is strongly degenerate with the Hubble constant H-0 and with inflationary parameters as the scalar spectral index n(s). These degeneracies may cause significant biases in the determination of cosmological parameters if a variation in alpha as large as similar to 0.5% is present at the epoch of recombination.