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.
