# Mass vs Peccei-Quinn scale

## Basic plot

### View Notebook (.ipynb)

### Download (.pdf)

### Download (.png)

## Plot with projections

### View Notebook (.ipynb)

### Download (.pdf)

### Download (.png)

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

- Beam EDM: limit, reference
- nEDM: limit, reference
- HfH+: limit, reference
- Piezoaxionic effect N=1, N=64 reference
- Storage Ring EDM: limit, reference
- CASPEr-electric projections: phase III, reference

## Other bounds

- BBN: limit, reference
- Black hole spins (Mehta et al.): limit, reference
- Black hole spins (Baryakhtar et al.) limit, reference
- Black hole spins (Unal et al.) limit, reference
- *Binary pulsars: limit, reference
- GW170817 limit, reference
- NS-NS Inspiral: projection, reference
- NS-BH Inspiral: projection, reference
- *Solar core (neutrino line): limit, reference
- SN1987A: limit, reference

(*) Using corrected values from here