The Accelerated Recombination, and the ACBAR and WMAP data
  We have investigated the deviation from the standard recombination process, using the ACBAR 2008 and the WMAP 3 year data. In this investigation, we have considered the possibility of the accelerated recombination as well as the delayed recombination. We find that the accelerated recombination is as likely as the delayed recombination, and there is some degeneracy between $\epsilon_{\alpha}$ and \{$n_s$, $\log[10^{10}A_s]$, $H_0$\}. 
Jaiseung Kim and Pavel Naselsky