Geant4 simulation of positron annihilation into 2 and 3 gamma

This work is devoted to the implementation of a new process to the Geant4 - the three-gamma-quantum annihilation of the electron-positron pair. It becomes particularly relevant since the proper estimation of this process via Monte-Carlo models is crucial for upcoming dark matter experiments. In the framework of this work the theoretical background on the problem was analyzed and a method of implementation of a new Geant4 models for 2-and 3-γ-annihilation was proposed and tested. Special unit test for new models was also prepared.