Axions, a Path to the Hot Dark Matter Bound

In recent years, significant progress in experimental technologies have brought within reach the possibility of detecting in terrestrial experiments the “invisible” axions. This sparked interest in the field, leading to numerous new theoretical and phenomenological studies, as well as to a plethora of experimental proposals (see [1–3] for recent reviews). Moreover, the ongoing experiments have already started to investigate the benchmark KSVZ/DFSZ axion models, with plans to delve deeper into the relevant parameter space in the coming decades. For this reason, it is of great importance, from the theory side, to push the “precision axion physics” in order to be ready to face any possible discovery.