WISP dark matter

WISPs are similar to WIMPs in some ways – e.g. they don’t interact very much at all with regular matter – but their key distinction is that they are very light in comparison. WISPs are many billions of times lighter, in fact, and much lighter than even the low mass WIMPs mentioned above. As a result of this, it is common these days to distinguish between WISPs and WIMPs by thinking of WIMPs as point-like particles (particle-like dark matter) and WISPs as more of a background field, or a wave (wave-like dark matter).

As WISPs are so light and wave-like, we don’t expect to detect them by waiting for them to bump into the nuclei of particles in our detector – we need to think differently about them, and rely on other interactions and detection methods.

The kinds of interactions we expect WISPs to have with regular matter depends on the flavour of WISP you are looking for. There are several few candidates that fall within the WISP umbrella, the most popular of which is a tiny, theoretical particle known as the axion.

The axion was proposed in the 1970s as part of a solution to what is known as the “Strong CP Problem”, which is one of the major outstanding problems in particle physics. It was later realized that axions, if they exist, would have the right properties to make up dark matter. So, if axions were detected, they could explain not only the Strong CP Problem, but account for dark matter as well, thus cleaning up two of the biggest problems in physics in a single blow!

As a result, axions have become very popular dark matter candidates, and there are a whole range of experiments around the world designed to search for them.