WMAP 5-year constraints on time variation of $\alpha$ and $m_e$
  We studied the role of fundamental constants in an updated recombination
scenario, focusing on the time variation of the fine structure constant \alpha
and the electron mass m_e in the early Universe. Using CMB data including WMAP
5-yr release, and the 2dFGRS power spectrum, we put bounds on variations of
these constants, when both constants are allowed to vary, and in the case that
only one of them is variable. In particular, we have found that -0.019 < \Delta
\alpha / \alpha_0 < 0.017 (95% c.l.), in our joint estimation of \alpha and
cosmological parameters. Finally, we analyze how the constraints depends on the
recombination scenario.
