The Strong CP Problem and a U(1)-Embedded Hiller–Schmaltz Framework for Ultralight Dark Matter and CKM Oscillations

by Ilay Bar (Weizmann)

Wednesday 28 Jan 2026, 12:30 → 13:30 Europe/Zurich

4/2-037 - TH meeting room (CERN)

The nature of the strong CP problem remains the subject of ongoing discussion: while the observed smallness of θˉ is often taken to indicate new physics, it is still worth examining whether this interpretation is strictly required. After reviewing the status of the problem and some of the proposed solutions, I will present a model based on the Hiller–Schmaltz (HS) mechanism in which CP is embedded into a continuous U(1) symmetry. In this framework, the HS mechanism naturally yields an ultralight dark-matter (ULDM) candidate in the form of a Goldstone boson, together with its full supermultiplet that needs to decouple at low energies. The resulting oscillatory ULDM field induces time-dependent modifications of the CKM flavor parameters. I will discuss the structure of the model, the origin of the Goldstone mode, and the phenomenological consequences for quark mixing, including potential observational signatures.