Primordial contribution to the matter bispectrum ($B_m^{\mathrm{prim}}$)

If the linear density contrast obeys $\delta (\mathbf{k})=\alpha (k)\phi (\mathbf{k})$, then local-type primordial non-Gaussianity contributesIn a squeezed bispectrum configuration and for a nearly scale-invariant potential, the leading term is $4f_{\mathrm{NL}}{P}_m(k_L)P_m(k_S)/\alpha (k_L)$. This excludes the standard perturbation theory in cosmology contribution from nonlinear gravity.