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

## TL;DR

This paper introduces a novel response approach to model the nonlinear halo squeezed-limit bispectrum, leveraging power spectrum responses to large-scale fluctuations, which aligns with perturbation theory and can be efficiently computed via simulations.

## Contribution

It demonstrates that the halo squeezed-limit bispectrum can be accurately modeled using power spectrum responses, providing a new method for nonlinear bispectrum modeling in cosmology.

## Key findings

- Second-order perturbation theory matches response calculations.
- Power spectrum responses can be obtained from separate universe simulations.
- Response approach offers a powerful tool for nonlinear bispectrum modeling.

## Abstract

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.