Hardi Veermäe will defend his doctoral thesis titled “Dark matter with long range vector-mediated interactions” on 27. October 2017 at 16:15 at W. Ostwaldi 1- A106.
Dr. Emidio Gabrielli, National Institute of Chemical Physics and Biophysics
Dr. Stefan Groote, Institute of Physics, University of Tartu
Dr. Martti Raidal, National Institute of Chemical Physics and Biophysics
Dr. Oleg Lebedev University of Helsinki, Helsinki, Finland
Dr. Enn Saar Tartu Observatory, Tartu, Estonia
Description of the problem
The existence of dark matter is supported by observations of several independent astrophysical phenomena such as galactic rotation curves, the cosmic microwave background and gravitational lensing. All these observations have one thing in common: they result solely from the gravitational interaction of dark matter. Numerous attempts to find non-gravitational interactions between the dark and visible sector have produced no results. The simplest dark matter models thus predict a single weakly interacting particle species. Accounting for the remarkable diversity of the elementary particles discovered so far, there is no reason to believe that five sixths of matter in the universe consists of a single non-interacting particle. For solving the problem of the nature of dark matter it is important to understand also the more complicated theoretical possibilities.
Result and benefit
The thesis combines four publications considering dark sector particles with electromagnetism type interactions. Such an interaction can arise if the dark matter particles carry a very small electric charge, dubbed the milli-charge. So far only milli-charged scalars and fermions have been considered in the literature. We extended the discussion to milli-charged vector bosons and proposed an experiment sensitive to the spin of milli-charged particles. Alternatively, the dark sector could contain its own dark electromagnetic force felt only by the dark sector particles. As a result of such an interaction dark matter could exist in a plasma state. If dark matter haloes composed of non-interacting dark matter will fly simply through each other, a dark plasma component can form shockwaves that will have an impact on the dark matter distribution. We numerically studied galaxy cluster collisions in a scenario where a fraction of dark matter is in a plasma state and found that this model can qualitatively reproduce the mass distribution observed in galaxy cluster collisions by weak lensing.