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Mass vs Peccei-Quinn scale


Basic plot

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Plot with projections

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Cosmological ALP scenarios and recasted constraints

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It must be noted that this plot and the 1/fa plot are, at best, challenging to interpret from any theoretical point of view. They should not be taken any more seriously than simply a comparison of experimental/observational sensitivities. The area outside of the QCD line here requires significant (and rarely natural) model-building. In essence one needs a “QCD” axion whose mass is different from than the mass arising just from the anomalous gluon coupling of the axion (which defines 1/f_a). There are very few models that achieve this naturally, such as the Z_N axion model of Hook (https://arxiv.org/abs/1802.10093), developed phenomenologically by Di Luzio et al. (https://arxiv.org/pdf/2102.00012.pdf)

Data files and references

Experiments

Other bounds

(*) Using corrected values from here