Abstract

The dark ages and cosmic dawn remain among the least explored epochs in our cosmic history. A powerful probe of these periods is the global 21-cm signal. With a growing number of experiments—such as REACH —approaching the sensitivity required to detect this signal, it is essential to develop robust tools for interpreting the forthcoming data. In this talk, I will introduce ECHO21 , a Python package I have developed for modelling the global 21-cm signal from the dark ages through cosmic dawn and up to the end of reionization. Built on an analytic framework, ECHO21 can generate a single signal in O(1) s, enabling the efficient computation of large model grids using multi-core parallelisation. This makes it ideally suited for astrophysical and cosmological inference from upcoming datasets. I will also present my recent work on modelling Lyman-α coupling. Conventional treatments typically neglect the effects of multiple scatterings of Ly-α photons. Our new framework incorporates both multiple scattering and inhomogeneities in the medium, leading to an RMS difference of up to 30% relative to standard calculations. I will conclude by outlining future directions and planned developments.