Abstract
We consider hadronic axion models that extend the Standard Model by one complex scalar field and one or more new heavy quarks, i.e. $N_\mathcal{Q} \geq 1$. We review previously suggested selection criteria as well as categorize and catalog all possible models for $N_\mathcal{Q} \leq 9$. In particular, allowing for $N_\mathcal{Q} > 1$ can introduce models that spoil the axion solution of the strong CP problem. Demanding that Landau poles do not appear below some energy scale limits the number of preferred models to a finite number. For our choice of criteria, we find that $N_\mathcal{Q} \leq 28$ and only 820 different anomaly ratios $E/N$ exist (443 when considering additive representations, 12 when all new quarks transform under the same representation). We analyze the ensuing $E/N$ distributions, which can be used to construct informative priors on the axion-photon coupling. The hadronic axion model band may be defined as the central region of one of these distributions, and we show how the band for equally probable, preferred models compares to present and future experimental constraints.
Highlights
QCD axions [1,2], initially proposed as a solution to the strong CP problem [3,4], are excellent cold dark matter (DM) candidates [5,6,7,8,9]
The single most powerful criterion amongst the ones proposed by Refs. [13,14] in the context of this work comes from the observation that representations with large C, I, or Y can induce Landau poles (LPs) at energies well below the Planck mass
We provide a catalog of all hadronic, or KSVZ, axion models with NQ ≤ 9, featuring 1,027,233,129 nonequivalent models in total
Summary
QCD axions [1,2], initially proposed as a solution to the strong CP problem [3,4], are excellent cold dark matter (DM) candidates [5,6,7,8,9]. To map and restrict the resulting landscape of axion models, it has been suggested that phenomenological selection criteria can be used to single out preferred models [13,14]. This allows us to restrict the parameter space and helps experiments to assess their sensitivity requirements. We summarize the construction of KSVZ-type axion models and phenomenological selection criteria in Secs. V we outline how the catalog of models can be used to construct informative prior distributions on E=N These can be used to define the KSVZ axion model band and we show how it compares to current and future experimental constraints. Model catalog and further supplementary material are available on Zenodo [15]
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