Spectrum of the axion dark sector
Spectrum of the axion dark sector
Axions arise in many theoretical extensions of the Standard Model of particle physics, in particular the ``string axiverse.'' If the axion masses, ${m}_{a}$, and (effective) decay constants, ${f}_{a}$, lie in specific ranges, then axions contribute to the cosmological dark matter and dark energy densities. We compute the background cosmological (quasi)observables …