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, room 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
The existence of dark matter follows from several independent astrophysical observations such as galactic rotation curves, the spatial distribution of temperature fluctuations of 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 interactions between the dark and visible sector besides the gravitational interaction have produced no results. Thus in the simplest models dark matter contain a single weakly interacting particle species. On the other hand, 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 obeys these simplest models. 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 charged 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. Alternatively, the dark sector could contain its own dark photon mediating a dark electromagnetic force felt only by the dark sector particles. As a result of such an interaction, all or a fraction of 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 cause shocks that will have an impact on the dark matter distribution after the collision. We numerically studied galaxy cluster collisions in a scenario where a fraction of dark matter is in a plasma state. We found that this model can qualitatively reproduce the mass distribution observed in galaxy cluster collisions by weak lensing.