Simulating Cosmological Axions in Primordial Magnetic Field

Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. The axion, a particle billions of times lighter than the electron that was proposed in the 1970s to solve the strong CP problem in the neutron, is now proving to be a strong candidate to explain this missing mass in the universe. Although there have been several experimental searches that have been conducted to detect axions, these efforts have not yet been fruitful because of the largely unconstrained mass of the axion. While static lattice simulations of the axion string cosmology have been able to constrain the mass to a certain extent, adaptive mesh refinement (AMR) algorithms have been able to do so far more effectively by being able to achieve dynamical ranges that are several orders of magnitude more than the ones achievable by static lattices. Our goal is to measure the emission spectrum of axion radiation from the strings, which are topological defects generated by the axion field. This is because the axion radiation and its energy spectrum determine the dark matter abundance today. The simulations that have been run so far have not taken into account the effects of how an external magnetic field would affect the evolution of the axion strings which have been proposed to be superconducting. The goal of the project is to compute how the abundance of dark matter is affected by this property precisely using large-scale numerical simulations of superconducting axion strings in an expanding universe with primordial magnetic fields.