# Constraining primordial non-Gaussianity using two galaxy surveys and CMB lensing

## TL;DR

This paper forecasts how future galaxy surveys and CMB lensing can tightly constrain primordial non-Gaussianity parameters, shedding light on early Universe perturbation mechanisms.

## Contribution

It introduces a combined multi-tracer and CMB lensing analysis to improve constraints on local non-Gaussianity and its scale dependence.

## Key findings

- Forecasted constraints: σ(f_NL) ≈ 0.9–1.4
- CMB lensing improves f_NL constraints by up to a factor of 2
- Potential to measure running of f_NL with σ(n_NL) ≈ 0.12–0.22

## Abstract

Next-generation galaxy surveys will be able to measure perturbations on scales beyond the equality scale. On these ultra-large scales, primordial non-Gaussianity leaves signatures that can shed light on the mechanism by which perturbations in the early Universe are generated. We perform a forecast analysis for constraining local type non-Gaussianity and its two-parameter extension with a simple scale-dependence. We combine different clustering measurements from future galaxy surveys -- a 21cm intensity mapping survey and two photometric galaxy surveys -- via the multi-tracer approach. Furthermore we then include CMB lensing from a CMB Stage 4 experiment in the multi-tracer, which can improve the constraints on bias parameters. We forecast $\sigma(f_{\rm NL}) \simeq 0.9$ (1.4) by combining SKA1, a Euclid-like (LSST-like) survey, and CMB-S4 lensing. With CMB lensing, the precision on $f_{\rm NL}$ improves by up to a factor of 2, showing that a joint analysis is important. In the case with running of $f_{\rm NL}$, our results show that the combination of upcoming cosmological surveys could achieve $\sigma(n_{\rm NL}) \simeq 0.12$ (0.22) on the running index.