Constraining Primordial non-Gaussianity with Bispectrum and Power Spectum from Upcoming Optical and Radio Surveys

TL;DR

This paper forecasts how upcoming optical and radio galaxy surveys can significantly improve constraints on primordial non-Gaussianity by using advanced bispectrum modeling that includes multiple effects and trispectrum contributions.

Contribution

It introduces a comprehensive PNG forecast combining bispectrum effects, including bias expansion, redshift distortions, uncertainties, and trispectrum, improving upon previous models.

Findings

Bispectrum can improve PNG bounds by up to a factor of 5.

Future surveys could measure f_NL^{loc} with an error of about 0.2.

Constraints on equilateral and orthogonal PNG are limited or comparable to current bounds.

Abstract

We forecast constraints on primordial non-Gaussianity (PNG) and bias parameters from measurements of galaxy power spectrum and bispectrum in future radio continuum and optical surveys. In the galaxy bispectrum, we consider a comprehensive list of effects, including the bias expansion for non-Gaussian initial conditions up to second order, redshift space distortions, redshift uncertainties and theoretical errors. These effects are all combined in a single PNG forecast for the first time. Moreover, we improve the bispectrum modelling over previous forecasts, by accounting for trispectrum contributions. All effects have an impact on final predicted bounds, which varies with the type of survey. We find that the bispectrum can lead to improvements up to a factor $\sim 5$ over bounds based on the power spectrum alone, leading to significantly better constraints for local-type PNG, with respect to current limits from \textit{Planck}. Future radio and photometric surveys could obtain a measurement error of $\sigma(f_{\mathrm{NL}}^{\mathrm{loc}}) \approx 0.2$. In the case of equilateral PNG, galaxy bispectrum can improve upon present bounds only if significant improvements in the redshift determinations of future, large volume, photometric or radio surveys could be achieved. For orthogonal non-Gaussianity, expected constraints are generally comparable to current ones.