Squeezing fNL out of the matter bispectrum with cosmological consistency relations

Mar 11, 2024 - 11:00 am to 12:00 pm

Campus, Varian 355

Sam Goldstein (Columbia) In Person and zoom https://stanford.zoom.us/my/sihanyuan?pwd=QnpsUHZWWGJ2ekVYWmZVL3BmM0gzZz09


Constraining the amplitude of local primordial non-Gaussianity (fNL) is a key goal of upcoming large-scale structure (LSS) surveys. Constraints on fNL from LSS surveys typically take advantage of the distinct imprint of local primordial non-Gaussianity on the large-scale galaxy power spectrum via the “scale-dependent bias.” A complementary approach is to constrain fNL directly from the bispectrum; however, this requires a robust model for the gravitational contribution to the bispectrum. Analytically modeling this gravitational non-Gaussianity with perturbative techniques can be particularly challenging for local fNL, where the primordial bispectrum peaks in the squeezed limit, i.e., when two of the wavenumbers are much larger than the third. In this talk, I will present an analytic model for the non-linear squeezed matter bispectrum in the presence of local fNL based on the LSS consistency relations — non-perturbative statements about the structure of LSS correlation functions derived from symmetries of the LSS equations of motion. Using measurements from Nbody simulations with and without local primordial non-Gaussianity, I will demonstrate that our model can be used to infer unbiased constraints on fNL well beyond the range of scales that can be modeled using conventional techniques, such as perturbation theory. I will then show how our results can be used to derive an estimator for fNL from squeezed configurations of CMB lensing and cosmic shear bispectra. Finally, I will present and validate a non-perturbative model for the collapsed matter trispectrum in the presence of local fNL based on LSS consistency relations.