Gravitational Lensing of Epoch-of-reionization Gas
Ue-Li Pen
TL;DR
This work assesses the feasibility of using weak gravitational lensing of 21 cm radiation from the epoch of reionization and beyond to constrain cosmology. It provides sensitivity estimates for upcoming radio arrays (PAST, LOFAR, SKA) and identifies three high-redshift lensing sources—reionization Stromgren spheres, large-scale structure, and minihalos—through which the weak-lensing signal can be measured. Tomography is shown to enable tracking the time evolution of the dark matter power spectrum, yielding percent-level constraints on parameters such as dark energy, neutrino mass, and cosmic equations of state, with potential inflationary gravity-wave signatures. The analysis further notes ultimate limits from observations of around $10^{18}$ minihalos, which could allow detection of inflationary Hubble scales $H_I$ down to $10^{-9} M_{Pl}$ and enable tests of backreaction and the quantum origin of perturbations.
Abstract
I present a weak lensing sensitivity estimate for upcoming high redshift (epoch of reionization and beyond) 21cm surveys. Instruments such as PAST, LOFAR and SKA should be able to measure the weak lensing power spectrum to precisions far exceeding conceivable optical surveys. Three types of sources are detectable, which include the re-ionization stromgren spheres, large scale structure, and minihalos. Tomography allows the measurement of the time evolution of the dark matter power spectrum. Raw sensitivities allow measurement of many cosmological parameters, including dark energy, neutrino mass and cosmic equations of state, to percent accuracy. It also has the potential for inflationary gravity wave measurements. Ultimate limits may be achievable through radio observations of 10^18 minihalos. Inflationary Hubble parameters H_I down to 10^-9 M_Planck can be detected through this effect. Second order effects may also be observable, allowing tests for backreaction and the quantum mechanical origin of perturbations.