Impact of Uncertainties in the Cosmological Parameters on the Measurement of Primordial non-Gaussianity

TL;DR

This paper evaluates how uncertainties in cosmological parameters affect the measurement of primordial non-Gaussianity, finding that these uncertainties can slightly increase the error margins, which is important for future precision cosmology.

Contribution

It quantifies the impact of cosmological parameter uncertainties on f_NL estimates and highlights the importance of marginalizing over these uncertainties in analyses.

Findings

Error propagation increases f_NL uncertainty by 16% for WMAP and 5% for Planck.

For a central f_NL value of 60, the correction for Planck is about 3.

Uncertainties become negligible if cosmological parameters are marginalized over.

Abstract

We study the impact of cosmological parameters' uncertainties on estimates of the primordial NG parameter f_NL in local and equilateral models of non-Gaussianity. We show that propagating these errors increases the f_NL 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 f_NL a central value of order 60, according to recent WMAP 5-years estimates, we obtain for Planck a final correction \Delta f_NL = 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 f_NL 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 f_NL error bar would become totally negligible if the parameters were allowed to vary in the analysis and then marginalized over.