Constraints on the Time Variation of the Fine Structure Constant by the 5-Year WMAP Data

The constraints on the time variation of the fine structure constant at recombination epoch relative to its present value, Delta alpha/alpha equivalent to (alpha(rec) - alpha(now)) / alpha(now), are obtained from the analysis of the 5-year WMAP cosmic microwave background data. As a result of Markov-Chain Monte-Carlo analysis, it is found that, contrary to the analysis based on the previous WMAP data, the mean value of Delta alpha/alpha = -0.0009 does not change significantly whether we use the Hubble Space Telescope (HST) measurement of the Hubble parameter as a prior or not. The resultant 95% confidence ranges of Delta alpha/alpha are -0.028 < Delta alpha/alpha < 0.026 with HST prior and -0.050 < Delta alpha/alpha < 0.042 without HST prior.