Department of Physics

Abstract: The QCD axion is a hypothetical particle proposed to solve the strong CP problem—why strong interactions preserve Charge-Parity symmetry—and has long been known to be an excellent dark matter candidate. Axion dynamics is well modeled by the phase direction of a classical and complex-valued field evolving in a wine-bottle potential. We have discovered novel axion dynamics in the early universe—a rotation in the complex-field space. Such rotations are a natural result of quantum gravity effects and inflationary dynamics. This dynamics was overlooked in the extensive literature but has profound consequences. For instance, axion rotations can simultaneously generate axion dark matter via “kinetic misalignment” and the observed excess of matter over antimatter in the Universe via “axiogenesis.” Remarkably, rich and correlated phenomenology automatically arises with sharp and distinct predictions. These include specific axion properties, unique gravitational wave signals, and correlated mass scales of supersymmetry and neutrinos. Axiogenesis in models with decaying heavy axions may be tested by neutrino experiments such as DUNE and long-lived particle searches at the LHC. Thus far, axion rotations have added fuel to experimental efforts and paved new theory research avenues, where resolutions to the deepest cosmological mysteries with discoverable signatures are underway or remain for discovery.