Decays of a NMSSM CP-odd Higgs in the low-mass region

Abstract

A popular regime in the NMSSM parameter space involves a light CP-odd Higgs A1. This scenario has consequences for e.g. light singlino Dark Matter annihilating in the A1-funnel. In order to confront the pseudoscalar to experimental limits such as flavour observables, Upsilon decays or Beam-Dump experiments, it is necessary to control the interactions of this particle with hadronic matter and derive the corresponding decays. The partonic description cannot be relied upon for masses close to {m_A}_{{}_1} ∼ 1GeV and we employ a chiral lagrangian, then extended to a spectator model for somewhat larger masses, to describe the interplay of the CP-odd Higgs with hadrons. Interestingly, a mixing can develop between A1 and neutral pseudoscalar mesons, leading to substantial hadronic decays and a coupling of A1 to the chiral anomaly. Additionally, quartic A1-meson couplings induce tri-meson decays of the Higgs pseudoscalar. We investigate these effects and propose an estimate of the Higgs widths for masses below {m_A}_{{}_1} ≲ 3 GeV. While we focus on the case of the NMSSM, our results are applicable to a large class of models.