C7 - WISPy Cold Dark Matter - From theory to experiment

Principal Investigators: J. Jaeckel (Heidelberg)


The project has the goal to investigate very light, very weakly interacting particles, so-called WISPs (for weakly interacting slim particles), as candidates for Dark Matter. A very well known example of such particles is the axion, but other types, well-motivated in extensions of the standard model, are more general axion-like particles and very light U(1) gauge bosons. The main aim of the project is to investigate the phenomenological properties of WISPy Dark Matter from its production to astrophysical and cosmological signatures in today’s universe, and to suggest improvements for existing experiments as well as develop new experimental search strategies. Despite their small mass WISPs can quite naturally be cold Dark Matter if produced non- thermally in the early universe. A very well known mechanism for this is the misalignment mechanism for the axion. But similar mechanisms may operate for other WISPs as well. While it is expected that WISPs produced in such a manner will behave like cold Dark Matter in many situations, in other cases it may lead to different signatures. For example, it has been suggested that (part of) it could form a Bose-Einstein condensate which would exhibit quite interesting cosmological properties and could significantly enhance the sensitivity of currently employed experimental searches. In other cases, WISPy Dark Matter may form small clumps, or, for particles with spin it may or may not preserve some directionality that can be probed in experiments. The first goal of the project is therefore to clarify these properties and the corresponding signals. WISPs can be cold Dark Matter candidates for a very wide range of masses and couplings. Direct detection experiments such as the ADMX haloscope, while being sensitive to extremely small couplings, can only probe axions and hidden photons in a limited mass range. It is therefore crucial to develop new methods that can test general WISPs in wider and/or complementary mass ranges. Experiments searching for WISPs, in particular those that search for WISPy Dark Matter, provide sensitivity to extremely small couplings. This is a typical feature of so-called hidden sectors and indeed WISPs appear in many models of fundamental physics. Theory can therefore provide valuable input on the preferred types of particles and the expected parameter ranges. Moreover, looking at concrete models allows to identify new features that can the be tested in experiment or observation. The third aim of this project is to fully exploit this interplay between model building and phenomenology and use it to open a new window to explore fundamental physics.