Axion global fits with Peccei-Quinn symmetry breaking before inflation
  using GAMBIT
  We present global fits of cosmologically stable axion-like particle and QCD
axion models in the mass range 0.1 neV to 10 eV. We focus on the case where the
Peccei-Quinn symmetry is broken before the end of inflation, such that the
initial value of the axion field can be considered to be homogeneous throughout
the visible Universe. We include detailed likelihood functions from
light-shining-through-wall experiments, haloscopes, helioscopes, the axion
relic density, horizontal branch stars, supernova 1987A, white dwarf cooling,
and gamma-ray observations. We carry out both frequentist and Bayesian
analyses, with and without the inclusion of white dwarf cooling. We explore the
degree of fine-tuning present in different models and identify parameter
regions where it is possible for QCD axion models to account for both the dark
matter in the Universe and the cooling hints, comparing them to specific DFSZ-
and KSVZ-type models. We find the most credible parameter regions, allowing us
to set (prior-dependent) upper and lower bounds on the axion mass. Our analysis
also suggests that QCD axions in this scenario most probably make up a
non-negligible but sub-dominant component of the dark matter in the Universe.
