Abstract
Solutions to the $\ensuremath{\mu}$ problem in supersymmetry based on the Kim-Nilles mechanism naturally feature a Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) axion with a decay constant of the order of the geometric mean of the Planck and TeV scales, consistent with astrophysical limits. We investigate minimal models of this type with two gauge-singlet fields that break a Peccei-Quinn symmetry and extensions with an extra vectorlike quark and lepton supermultiplets consistent with gauge coupling unification. We show that there are many anomaly-free discrete symmetries, depending on the vectorlike matter content, that protect the Peccei-Quinn symmetry to sufficiently high order to solve the strong $CP$ problem. We study the axion couplings in this class of models. Models of this type that are automatically free of the domain wall problem require at least one pair of strongly interacting vectorlike multiplets with mass at the intermediate scale and predict axion couplings that are greatly enhanced compared to the minimal supersymmetric DFSZ models, putting them within reach of proposed axion searches.
Highlights
Extensions of the Standard Model (SM) of particle physics are plagued by several apparent hierarchy problems, which can be viewed as hints toward the ultimate completion of the theory
II, we review the general properties of axion models, in particular, the relation between PQ charge assignments and axion couplings, the domain wall problem, and the axion quality problem
We considered supersymmetric DFSZ-type axion models with the field content of the minimal supersymmetric Standard Model (MSSM) plus two gauge-singlet fields X and Y that spontaneously break the PQ symmetry and some extra vectorlike quark and lepton supermultiplets
Summary
Extensions of the Standard Model (SM) of particle physics are plagued by several apparent hierarchy problems, which can be viewed as hints toward the ultimate completion of the theory. The axion quality problem [30,31,32,33,34] results from the possible presence of higher-dimensional contributions to the Lagrangian that explicitly violate the Uð1Þ PQ symmetry, since these can displace the QCD θ parameter away from 0 at the minimum of the scalar potential, spoiling the solution to the strong CP problem.
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