Searching for dark matter at colliders

Dark Matter (DM) detection prospects at future $$e^+e^-$$ colliders are reviewed under the assumption that DM particles are fermions of the Majorana or Dirac type. Although the discussion is quite general, one will keep in mind the recently proposed candidate based on an excess of energetic photons observed in the center of our Galaxy with the Fermi-LAT satellite. In the first part we will assume that DM interactions are mediated by vector bosons, $$Z$$ or $$Z'$$. In the case of $$Z$$-boson Direct Detection limits force only axial couplings with the DM. This solution can be naturally accommodated by Majorana DM but is disfavored by the GC excess. Viable scenarios can be instead found in the case of $$Z'$$ mediator. These scenarios can be tested at $$e^{+}e^{-}$$ colliders through ISR events, $$e^+e^-\rightarrow XX+\gamma $$. A sensitive background reduction can be achieved by using highly polarized beams. In the second part scalar particles, in particular Higgs particles, have been considered as mediators. The case of the SM Higgs mediator is excluded by limits on the invisible branching ratio of the Higgs. On the contrary particularly interesting is the case in which the DM interactions are mediated by the pseudoscalar state $$A$$ in two Higgs-doublet model scenarios. In this last case the main collider signature is $$e^+e^-\rightarrow HA, H\rightarrow hh, A \rightarrow XX$$