CA21106 - COSMIC WISPers in the Dark Universe: Theory, astrophysics and experiments (CosmicWISPers)

Axions and other very weakly interacting slim (m<GeV) particles (WISPs) are easily accommodated in several extensions of the Standard Model of Particle Physics. They may be non-thermally produced in the early universe and survive as constituents of the dark universe. The aim of this Action is an exhaustive study of these WISPs, notably axions, axion-like particles (ALPs) and hidden photons (HP), ranging from their theoretical underpinning, over their indirect observational consequences in astrophysics, to their search at colliders and beam-dump and their direct detection in laboratory experiments. Searches for WISPs are strongly motivated by our attempts to understand the nature of the dark matter and puzzling astrophysical and particle physics observations. A rich, diverse, and low-cost experimental program is already underway that has the potential for one or more game-changing discoveries. The aim of this Action is to coordinate and support WISPs searches in a synergic way at the boundary between particle physics, astrophysics and cosmology. It will provide a platform to benefit from the latest data from laboratory and astrophysical experiments. It will also offer a guidance for experimental efforts and theoretical investigations dealing with fundamental questions, like the strong CP problem and the nature of the dark matter.