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

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 $f_{\mathrm{NL}}^{loc.}$ 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 $1\sigma (f_{\mathrm{NL}}^{\text{loc.}})=300$, while an ideal experiment will achieve $1\sigma (f_{\mathrm{NL}}^{\text{loc.}})=130$, 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 $f_{\mathrm{NL}}^{\text{loc.}}$ boundaries from {\em Planck}, but we stress again that they refer to completely different scales.

24 pages, 5 figures

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• Non-Gaussianity constraints from Planck spectral distortion cross-correlations
• Spectral Distortion Anisotropy from Inflation for Primordial Black Holes
• Primordial tensor bispectra in $\mu$-CMB cross-correlations
• Leverage on small-scale primordial non-Gaussianity through cross-correlations between CMB $E$-mode and $\mu$-distortion anisotropies
• Spectral Distortion Signatures of Step-like Inflationary Potential