The halo squeezed-limit bispectrum with primordial non-Gaussianity: a power spectrum response approach

Modeling the nonlinearity of the halo bispectrum remains a major challenge in modern cosmology, in particular for ongoing and upcoming large-scale structure observations that are performed to study the inflationary physics. The "power spectrum response" offers a solution for bispectrum in the so-called squeezed limit, in which one wavenumber is much smaller than the other two. As a first step, we demonstrate that the halo squeezed-limit bispectrum computed from the second-order standard perturbation theory agrees precisely with the responses of linear halo power spectrum to large-scale density and potential fluctuations. Since the halo power spectrum responses to arbitrarily small scales can straightforwardly be obtained by separate universe simulations, the response approach provides a novel and powerful technique for modeling the nonlinear halo squeezed-limit bispectrum.