Project Level: PhD

Despite overwhelming astronomical and cosmological evidence for its existence, the microscopic composition of dark matter remains a complete mystery.

The vast majority of the effort to detect dark matter has focused on weakly interacting massive particles (WIMPs), with masses ~10 – 1000 GeV. WIMPs in that mass range may scatter off atomic nuclei leaving detectable recoil energy in experiments. However, this represents only a tiny sliver of the possible mass range for dark matter particles, which may have masses down to < ~ 10^(-20) eV. Current experiments are blind to the majority of this parameter space.

Taking advantage of atomic (rather than nuclear) phenomena, however, may drastically increase the range of masses we can search for.

As the dark matter (DM) mass drops much below the nucleus mass (<GeV), no appreciable nuclear recoils are observable. However, DM particles may instead scatter of atomic electrons, leading to observable ionisations. As the DM mass drops below that of the electron (<~MeV), there are no detectable electron recoils, however, a detectable signal may instead come from DM absorption ("dark" photoelectric effect). Finally, as the DM mass drops below the ~eV scale, it behaves as a classical radiation field. Then, the observable effect comes in the form of atomic interactions with the classical DM field, such as energy shifts caused by dark-matter-induced effective variation of fundamental constants.

Combining ideas from particle astrophysics with theoretical atomic physics, this project is to identify and quantify new observable effects that can be used to search for evidence of new particles and fields, which may be due to dark matter, dark energy, or something even more exotic.

In particular, it will involve investigating and calculating rates of scattering, absorption, energy-level shifts in atomic systems.

Project members

Dr Benjamin Roberts