``The physics case for low energy photon experiments''

Abstract:

Over the years we have accumulated a large number of indications for physics
beyond the standard model. This new physics is often sought-after at high
masses and energies. However, over recent years it has become increasingly
clear that new physics can also appear at low energy, but extremely weak
coupling. Experiments and observations at this `low energy frontier'
therefore provide a powerful tool to gain insight into fundamental physics,
which is complementary to accelerators.

In particular, we argue that there exists an excellent `physics case'
motivating the search for axions, WISPs (very weakly interacting sub-eV
particles) and other phenomena testable in low energy experiments with
photons. This physics case arises from both experimental and observational
evidence as well as the desire to test theoretical model building.