Speaker
Description
The quantum chromodynamics (QCD) axion, which may explain the absence of a neutron electric dipole moment, arises as the pseudo-Goldstone mode of a spontaneously broken abelian Peccei-Quinn (PQ) symmetry. If the scale of PQ symmetry breaking occurs below the inflationary reheat temperature, then there is a unique axion mass that gives the observed dark matter (DM) abundance. Computing this mass has been the subject of intensive numerical simulations for decades, since the mass prediction informs laboratory experiments that are only able to target narrow mass ranges. In this work we perform the most precise and accurate large-scale simulations to-date of the axion-string network using adaptive mesh refinement to achieve the precision that would otherwise require a static lattice with $262,144^3$ lattice sites. Furthermore, we perform a suite of smaller, systematic simulations to account for axions produced during the QCD phase transition from the string-domain-wall-network collapse and to account for transient aspects of the initial state. These new simulations provide new insights on the dynamics of topological defects and sharpen predictions for the mass of the axion which comprises all the dark matter.
