= Primordial contribution to the matter bispectrum
{title2=$B_m^{\rm prim}$}
If the linear <density contrast> obeys $\delta(\mathbf k)=\alpha(k)\varphi(\mathbf k)$, then <local-type primordial non-Gaussianity> contributes
$$
B_m^{\rm prim}=2f_{\rm NL}\left[\frac{\alpha_3}{\alpha_1\alpha_2}P_m(k_1)P_m(k_2)+\text{cyclic terms}\right].
$$
In a <squeezed bispectrum configuration> and for a nearly scale-invariant potential, the leading term is $4f_{\rm NL}P_m(k_L)P_m(k_S)/\alpha(k_L)$. This excludes the <standard perturbation theory in cosmology> contribution from nonlinear gravity.
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