Primordial non-Gaussianity with $\mu$-type and $y$-type spectral distortions: exploiting Cosmic Microwave Background polarization and dealing with secondary sources

TL;DR

This paper proposes new methods to measure primordial non-Gaussianity using spectral distortions of the CMB, specifically by leveraging polarization data and cleaning techniques to mitigate secondary contamination, aiming to access different primordial scales.

Contribution

It introduces innovative approaches combining polarization correlations and template cleaning to improve constraints on primordial non-Gaussianity from spectral distortions.

Findings

Forecasts show improved sensitivity with combined methods.

Adding $y$-$E$ polarization data enhances detection prospects.

Template cleaning reduces noise, improving constraints.

Abstract

Cross-correlations between Cosmic Microwave Background (CMB) temperature and $y$-spectral distortions anisotropies have been previously proposed as a way to measure the local bispectrum parameter $f_{\rm NL}^{\rm loc.}$ in a range of scales inaccessible to either CMB ($T$, $E$) bispectra or $T$-$\mu$ correlations. This is useful e.g. to test scale dependence of primordial non-Gaussianity. Unfortunately, the primordial $y$-T signal is strongly contaminated by the late-time correlation between the Integrated Sachs Wolfe and Sunyaev-Zel'dovich (SZ) effects. Moreover, SZ itself generates a large noise contribution in the $y$-parameter map. We consider two original ways to address these issues. In order to remove the bias due to the SZ-CMB temperature coupling, while also adding new signal, we include in the analysis the cross-correlation between $y$-distortions and CMB {\em polarization}. In order to reduce the noise, we propose to clean the $y$-map by subtracting a SZ template, reconstructed via cross-correlation with external tracers (CMB and galaxy-lensing signals). We combine this SZ template subtraction with the previously adopted solution of directly masking detected clusters. Our final forecasts show that, using $y$-distortions, a PRISM-like survey can achieve $1\sigma(f_{\rm NL}^\text{loc.}) = 300$, while an ideal experiment will achieve $1\sigma(f_{\rm NL}^\text{loc.}) = 130$, with improvements of a factor $\sim 3$ from adding the $y$-$E$ signal, and a further $20-30 \%$ from template cleaning. These forecasts are much worse than current $f_{\rm NL}^\text{loc.}$ boundaries from {\em Planck}, but we stress again that they refer to completely different scales.