2026/01/05 by Hitoshi Murayama · 1 voice
Physics and Astronomy · #hep-ph #hep-ex
arxiv published 2026/01/05 · arxiv updated 2026/01/23
In order to solve the strong CP problem, we study the possibility that the Peccei--Quinn symmetry is broken \it below\/ the QCD scale. We find that a QCD axion can be above GeV, and may be among the observed η resonances. It is immune to quantum gravity corrections. The only fermion that has a U(1) Peccei--Quinn charge is the right-handed up quark. Flavor-changing neutral currents are surprisingly small. All accelerator and astrophysical limits can be evaded. The most significant constraint is the mass splitting between π^± and π0. In a UV completed model, LHC can look for a heavy quark pair \cal D \cal D followed by the decay \cal D → W+u or a single production q u → q \cal U followed by \cal U → u Z, uh. There can be an O(1) contribution h → uuφ in the measurement of h → gg or permille effects on the hadronic Z width at a Higgs factory.