# CMB-S4 forecast on the primordial non-Gaussianity parameter of feature models

## TL;DR

This paper forecasts the constraints on primordial non-Gaussianity parameter $f_ ext{NL}$ for feature models using future CMB-S4 experiments, introducing a novel covariance orthonormalisation method to improve computation.

## Contribution

It presents new forecast methods for $f_ ext{NL}$ constraints in CMB-S4, including a novel covariance matrix orthonormalisation technique, and compares sensitivities to Planck and Simons Observatory.

## Key findings

- CMB-S4 could improve $f_ ext{NL}$ constraints by up to 2.2 times over Planck.
- Baseline CMB-S4 conditions yield 1.3-1.6 times better constraints than Planck.
- Temperature and E-mode polarization data are crucial for detecting oscillatory features.

## Abstract

We present forecasts on the primordial non-Gaussianity parameter $f_\text{NL}$ of feature models for the future Cosmic Microwave Background Stage-4 (CMB-S4) experiments. The Fisher matrix of the bispectrum estimator was computed using noise covariances expected for preliminary CMB-S4 specifications including ones for the Simons Observatory. We introduce a novel method that improves the computation by orthonormalising the covariance matrix. The most sensitive CMB-S4 experiment with 1' beam and 1$\mu K$-arcmin noise would yield a factor of 1.7-2.2 times more stringent constraints compared to Planck. Under the Simons Observatory baseline conditions the improvement would be about 1.3-1.6 times to Planck. We also thoroughly studied the effects of various model and experimental parameters on the forecast. Detailed analysis on the constraints coming from temperature and E-mode polarisation, in particular, provided some insight into detecting oscillatory features in the CMB bispectrum.