Centered quadratic Gaussian transformation
= Centered quadratic Gaussian transformation
{title2=$G+\alpha(G^2-\langle G^2\rangle)$}
If $G$ is a centered <Gaussian random field>, the transformation $G+\alpha(G^2-\langle G^2\rangle)$ retains zero mean and introduces a three-point <connected correlation function> at first order in $\alpha$. <Wick contractions> give $2\alpha$ times the sum of products of two covariances. The corresponding local cosmological model uses $\alpha=3f_{\mathrm{NL}}/5$.