Axions are compelling candidates for physics beyond the standard model, and occur ubiquitously in string theory models. I will show that a class of theories with very light axions can produce cosmic strings in the sky today which have remarkable signals. Photons propagating around the string undergo a model-independent polarization rotation that can help measure the fundamental quantum of charge in the standard model. Remarkably, the size of the expected signal from the CMB is at the sensitivity of current experiments, with future experiments expected to improve by orders of magnitude. As the strings pass through galactic magnetic fields, they build up localized charge and current density traveling along the string. This sets up a cosmological plasma collider where collisions can occur at very high energies and produce interesting astrophysical signals.
Prateek Agrawal finished his PhD in theoretical particle physics at the University of Maryland. After postdoc positions at Fermilab and Harvard, Prateek moved to a Associate Professor position at the University of Oxford. His research interests lie broadly in physics beyond the standard model and its signals. His recent work includes new mechanisms in axion physics and phenomenological implications of the string swampland program.