Abstract
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.
Highlights
QCD axions [1,2,3,4] and axion-like particles (ALPs) are perhaps among the most intriguing classes of hypothetical particles
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
In this study we presented the first global fits of axion models in the pre-inflationary PQ symmetry-breaking scenario, using frequentist and Bayesian methods
Summary
QCD axions [1,2,3,4] and axion-like particles (ALPs) are perhaps among the most intriguing classes of hypothetical particles. Because QCD axions can behave as cold dark matter (DM) [6,7,8,9], the interesting regions of the parameter space are where they contribute significantly to the DM density of the Universe. If so, they would solve at least two outstanding problems in physics at the same time (the other being the Strong CP problem [1, 2]). We can learn more about the parameter space of different models, help guide the planning of future searches towards the most promising search areas and — if axions do exist — find them in the correlated signals of several experiments and determine their properties
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
