What’s the nature of dark matter? has become one of the most important questions in modern particle physics and cosmology. The QCD axion, hypothetical particle arising in the Peccei-Quinn-Weinberg-Wilczek “mechanism” to explain the shocking absence of CP violation in the strong interactions (“strong-CP problem”) is one of the leading candidates. Unfortunately, so far it has received comparatively less attention than the “weakly-interacting-massive-particles” WIMPs. The QCD axion, as a very weakly interacting and small-mass particle, behaves in very different ways than a WIMP promising very distinct phenomenology and demanding extraordinarily different experimental searches.

In the last decade there has been a steady increase in the study of the theory and phenomenology of axion dark matter and a parallel interest has grown in the experimental community. The QCD axion has been generalised to axion-like particles (ALPs) and more broadly to weakly-interacting-slim particles (WISPs). Many new experimental techniques have been proposed and R&D projects have been launched to test them. With such a strain, important aspects of the theory of axion DM lag behind the experimental developments and will not be ready to interpret accurately the results of axion DM searches expected during the next decade. Furthermore, certain ranges of parameter space are currently untargeted by any realistic experimental technique.

In this workshop we will address the most relevant questions still open today in axion dark matter phenomenology by putting together scientists with the relevant expertise.