Quark flavor phenomenology of the QCD axion
Jorge Martin Camalich (Instituto de Astrofísica de Canarias, s/n, E-38205, La Laguna, Tenerife, Spain, Departamento de Astrofísica, Universidad de La Laguna, E-38206, La Laguna, Tenerife, Spain); Maxim Pospelov (School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA, William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA); Pham Ngoc Hoa Vuong (Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-Alpes, CNRS/IN2P3, Grenoble INP, 38000 Grenoble, France); Robert Ziegler (Institut für Theoretische Teilchenphysik (TTP), Karlsruher Institut für Technologie (KIT), 76131 Karlsruhe, Germany, Theoretical Physics Department, CERN, 1 Esplanade des Particules, 1211 Geneva 23, Switzerland); Jure Zupan (Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221, USA)
Axion models with generation-dependent Peccei-Quinn charges can lead to flavor-changing neutral currents, thus motivating QCD axion searches at precision flavor experiments. We rigorously derive limits on the most general effective flavor-violating couplings from current measurements and assess their discovery potential. For two-body decays, we use available experimental data to derive limits on decay rates for all flavor transitions. Axion contributions to neutral-meson mixing are calculated in a systematic way using chiral perturbation theory and operator product expansion. We also discuss in detail baryonic decays and three-body meson decays, which can lead to the best search strategies for some of the couplings. For instance, a strong limit on the transition can be derived from the supernova SN 1987A. In the near future, dedicated searches for decays at ongoing experiments could potentially test Peccei-Quinn breaking scales up to at NA62 or KOTO and up to at Belle II or BES III.
