Cosmological forecast from the full-sky angular power spectrum and bispectrum of 21cm intensity mapping

TL;DR

This paper forecasts cosmological parameter constraints from full-sky 21cm intensity mapping using power spectrum and bispectrum, highlighting the bispectrum's role in probing dark energy and improving parameter precision.

Contribution

First full-sky relativistic bispectrum forecast for 21cm surveys, demonstrating its significance in constraining dark energy parameters and improving cosmological measurements.

Findings

Velocity contribution accounts for 24% of the signal at low redshift.

Bispectrum constraints are comparable to power spectrum for standard models.

Joint analysis improves constraints on dark energy parameters by over 70%."

Abstract

We compute the full-sky angular power spectrum and bispectrum, along with their Fisher matrices, to forecast constraints on cosmological parameters for the BINGO and SKA1-MID Band 2 radio telescopes. This represents the first forecast analysis using the full-sky relativistic bispectrum in redshift space for these surveys. Our results show that the second-order velocity contribution, often neglected under the Limber approximation, accounts for approximately $24\%$ of the total signal at low redshifts, indicating that it must be included for accurate modeling. Using these forecasts, we find that while the bispectrum provides constraints comparable to the angular power spectrum for $\Lambda$CDM and ${\rm w}$CDM models, it becomes a powerful probe of dynamical dark energy. Restricting the analysis to linear scales, we show that the inclusion of the bispectrum yields a substantial improvement in the determination of the Chevallier-Polarski-Linder (CPL) parameters. In particular, the joint analysis of the bispectrum, power spectrum, and Planck CMB data improves constraints on ${\rm w}_0$ and ${\rm w}_a$ by over $70\%$, and the Hubble parameter $h$ by approximately $60\%$. These results underscore the importance of relativistic bispectrum for breaking parameter degeneracies and probing the nature of dark energy with upcoming large-scale structure surveys.