RTS: 21-cm cosmology after 2021

Dark Side (WH6NW) (Fermilab)

Dark Side (WH6NW)


The universe is full of neutral hydrogen that shines in the 21-cm spin-flip transition. Mapping the large scale structure of the universe in 3D using this line is in principle extremely cheap and simple, but has in practice proven to be quite difficult. In this talk, I will argue that this technique nevertheless offers the most promising way to complete the programmatic goal of measuring the linear scales of the universe deep into the pre-acceleration era after the current crop of optical experiments complete observing. It will give us expansion history measurements to z=6 using Baryon Acoustic Oscillations, several new screens to study weak gravitational lensing, allow unprecedented constraints on primordial non-Gaussianity, and perhaps even allow direct measurements of the real-time expansion of the universe. I will discuss the scientific, technological and programmatic issues that we need to overcome to make such an experiment a reality. This presentation is based on the recent white-paper arguing for a Stage II 21cm experiment within the US DOE Cosmic Visions Dark Energy (arXiv:1810.09572).