Loop-induced annihilation of dark matter

Plenty of evidences suggest the existence of a new type of non-luminous matter in the Universe, that has been called dark matter. Its nature is still unresolved, however, there is a widespread belief that is a new particle. Today we have three important search strategies for dark matter: indirect detection, direct detection and collider searches. In this thesis we focus on indirect detection, which investigates the products of annihilation of dark matter in overdense regions of the Universe. In particular we focus on gamma-ray observations, considering the gamma-ray line signal, arising from dark matter annihilation into a pair of monochromatic photons. For electrically neutral dark matter, this process can proceed only via loop diagrams. Its computation can be done using numerical techniques. Numerical tools are a huge step forward in the dark matter research, and help scientists to make predictions and improve their models. However, at the current status there is no tool allowing for the calculation of loop-induced gamma-ray signals for arbitrary models. In this thesis we make an important step towards filling this gap. We focus on the numerical tool MadDM, and we validate the feature of automatised loop-induced computation using two dark matter models: the singlet scalar Higgs portal model and a simplified top-philic model. We then constrain the parameter space of these models using the current experimental results. In particular we consider the upper limits on gamma-ray line searches obtained by Fermi-LAT and HESS collaborations, finding that they provide important constraints on the parameters of both models.