Estimating the impact of recombination uncertainties on the cosmological parameter constraints from cosmic microwave background experiments

We use our most recent training set for the RICO code to estimate the impact of recombination uncertainties on the posterior probability distributions which will be obtained from future cosmic microwave background experiments, and in particular the Planck satellite. Using a Monte Carlo Markov Chain (MCMC) analysis to sample the posterior distribution of the cosmological parameters, we find that Planck will have biases of -0.7, -0.3 and -0.4 for n S , b h 2 and log(10 10 A S ), respectively, in the minimal six-parameter cold dark matter model, if the description of the recombination history given by RICO is not used. The remaining parameters (e.g. or dm h 2 ) are not significantly affected. We also show that the cosmology dependence of the corrections to the recombination history modelled with RICO has a negligible impact on the posterior distributions obtained for the case of the Planck satellite. In practice, this implies that the inclusion of additional corrections to existing recombination codes can be achieved using simple cosmology-independent 'fudge functions'.