Spring 2026 Colloquium: New Perspectives on the QCD Axion

Abstract: The QCD axion is a compelling candidate to explain why the neutron shows no measurable electric dipole moment, providing a dynamical resolution of the strong CP problem. Remarkably, the same particle can also account for the dark matter of the universe. After a brief introduction to the basic idea, I will describe new perspectives that go beyond the minimal picture, including the origin of the axion’s fundamental scale, how the underlying symmetry can be protected from quantum gravity, and mechanisms that modify the axion mass while still solving the strong CP problem. Together, these ideas can significantly redirect experimental search strategies and open qualitatively new possibilities for axion cosmology in the early universe