Breaking degeneracies with the Sunyaev-Zeldovich full bispectrum

TL;DR

This paper demonstrates that the full bispectrum of the thermal Sunyaev-Zeldovich effect significantly enhances parameter constraints, surpassing the power spectrum, by effectively breaking degeneracies through detailed shape analysis.

Contribution

It provides a comprehensive Fisher analysis including complete covariance, foreground modeling, and an extended parameter set, showing the bispectrum's superior constraining power over the power spectrum.

Findings

Bispectrum tightens constraints on cosmological parameters.

Shape dependence of triangle types aids in breaking degeneracies.

Parameter uncertainties reduce significantly with bispectrum inclusion.

Abstract

Non-Gaussian (NG) statistics of the thermal Sunyaev-Zeldovich (tSZ) effect carry significant information which is not contained in the power spectrum. Here, we perform a joint Fisher analysis of the tSZ power spectrum and bispectrum to verify how much the full bispectrum can contribute to improve parameter constraints. We go beyond similar studies of this kind in several respects: first of all, we include the complete power spectrum and bispectrum (auto- and cross-) covariance in the analysis, computing all NG contributions; furthermore we consider a multi-component foreground scenario and model the effects of component separation in the forecasts; finally, we consider an extended set of both cosmological and intra-cluster medium parameters. We show that the tSZ bispectrum is very efficient at breaking parameter degeneracies, making it able to produce even stronger cosmological constraints than the tSZ power spectrum: e.g. the standard deviation on $\sigma_8$ shrinks from $\sigma^\text{PS}(\sigma_8)=0.35$ to $\sigma^\text{BS}(\sigma_8)=0.065$ when we consider a multi-parameter analysis. We find that this is mostly due to the different response of separate triangle types (e.g. equilateral and squeezed) to changes in model parameters. While weak, this shape dependence is clearly non-negligible for cosmological parameters, and it is even stronger, as expected, for intra-cluster medium parameters.