A big chunk of my work is on how to learn cosmology and astrophysics from 21-cm data. Here are some examples:
In two companion papers (1 and 2) I introduced 21cmvFAST, a version of 21cmFAST that included the effect of the dark matter-baryon relative velocities on the first galaxies. I showed that these produce velocity-induced acoustic oscillations (VAOs, or wiggles) in the 21-cm signal during cosmic dawn, which can be used as a standard ruler to cosmic dawn (z=10-20). In this paper I made the velocities part of the standard 21cmFAST software, and updated our reference 21-cm models of the first galaxies (see EOS21 for details and nice animations).
I have also developed the 21-cm line as a tool to learn about dark matter (DM). Here we argued that cosmic dawn is an ideal location to search for millicharged DM, and that only a sub-percent fraction of the DM is required to explain the EDGES anomaly at z=17. I have led the HERA theory analysis of DM, and found more stringent limits, though at z=8-10. Upcoming high-z HERA data will be able to test the origin of the EDGES depth, if real. The 21-cm line also has information about the timing of the first galaxies, which in this paper I showed makes it is sensitive to the small-scale nature of dark matter, at much higher wavenumbers than currently accessible (k~50/Mpc). This can help identify self-interacting DM, like in the ETHOS models.
The future of 21-cm is to map the fluctuations across many redshifts and scales, which show a rich phenomenology of processes, ranging from heating of the IGM (likely due to high-mass X-ray binaries), to its reionization (due to galaxies of different masses). Key to understand all these processes are fast simulations across a range of scales. These are needed to explore the vast astrophysical---and cosmological---parameter space. Below I show a lightcone of the 21-cm signal across cosmic dawn and the EoR, along with the densities that seed the fluctuations.
These are not just beautiful theoretical pictures, but also signals to compare with the results of current and upcoming 21-cm experiments. I'm a member of HERA, where we have been able to set the deepest limits on the 21-cm power spectrum during reionization (z=8-10), and are now pushing to do the same at cosmic dawn (z=14-20). I lead the dark-matter theory group in HERA, and have worked on translating the 21-cm limits into inferences on the spin temperature of gas during unexplored eras. See for instance the plot I made with a summary of the first HERA limits, in our first interpretation paper (see also the most recent one, with a similar plot, here).