Impact of Uncertainties in the Cosmological Parameters on the Measurement of Primordial non-Gaussianity
Abstract
We study the impact of cosmological parameters' uncertainties on estimates of the primordial NG parameter fNL in local and equilateral models of non-Gaussianity. We show that propagating these errors increases the fNL relative uncertainty by 16% for WMAP and 5 % for Planck in the local case, whereas for equilateral configurations the correction term are 14% and 4%, respectively. If we assume for local fNL a central value of order 60, according to recent WMAP 5-years estimates, we obtain for Planck a final correction fNL = 3. Although not dramatic, this correction is at the level of the expected estimator uncertainty for Planck, and should then be taken into account when quoting the significance of an eventual future detection. In current estimates of fNL the cosmological parameters are held fixed at their best-fit values. We finally note that the impact of uncertainties in the cosmological parameters on the final fNL error bar would become totally negligible if the parameters were allowed to vary in the analysis and then marginalized over.