CMBR Weak Lensing and HI 21-cm Cross-correlation Angular Power Spectrum

TL;DR

This paper explores the cross-correlation between weak lensing of the CMBR and the 21-cm emission from neutral hydrogen, proposing it as a new probe for understanding large-scale structure and cosmology.

Contribution

It introduces the concept of cross-correlating CMBR weak lensing with HI 21-cm signals to enhance cosmological parameter estimation and LSS studies.

Findings

Cross-correlation proportional to the dark matter power spectrum.

Significant detection of the cross-correlation is theoretically possible.

Potential to improve CMBR de-lensing and cosmological constraints.

Abstract

Weak gravitational lensing of the CMBR manifests as a secondary anisotropy in the temperature maps. The effect, quantified through the shear and convergence fields imprint the underlying large scale structure (LSS), geometry and evolution history of the Universe. It is hence perceived to be an important observational probe of cosmology. De-lensing the CMBR temperature maps is also crucial for detecting the gravitational wave generated B-modes. Future observations of redshifted 21-cm radiation from the cosmological neutral hydrogen (HI) distribution hold the potential of probing the LSS over a large redshift range. We have investigated the correlation between post-reionization HI signal and weak lensing convergence field. Assuming that the HI follows the dark matter distribution, the cross-correlation angular power spectrum at a multipole \ell is found to be proportional to the cold dark matter power spectrum evaluated at \ell/r, where r denotes the comoving distance to the redshift where the HI is located. The amplitude of the ross-correlation depends on quantities specific to the HI distribution, growth of perturbations and also the underlying cosmological model. In an ideal ituation, we found that a statistically significant detection of the cross-correlation signal is possible. If detected, the cross-correlation signal hold the possibility of a joint estimation of cosmological parameters and also test various CMBR de-lensing estimators.