The axion mass
Abstract: The quantum chromodynamics axion is a well motivated new physics candidate that can explain the strong-CP problem related to the neutron electric dipole moment in addition to the dark matter (DM) in our Universe. However, if the axion is generated after inflation, then only one axion mass is expected to give rise to the correct DM abundance. Computing this mass requires numerical simulations of axion strings and their radiation. I will describe our most recent state-of-the-art simulations of this cosmology and our resulting predictions for the axion mass. If the axion is generated before inflation, then there is a less direct relationship between its mass and its cosmological abundance. In fact, I will describe preliminary work towards a model of MeV-mass axion-like particles that make up the correct DM abundance by coupling to a dark gauge group, whose glueballs lead to a period of early matter domination in the early Universe.