Fully Geant4 compatible package for the simulation of Dark Matter in fixed target experiments

We present the package for the simulation of DM (Dark Matter) particles in fixed target experiments. The most convenient way of this simulation (and the only possible way in the case of beam-dump) is to simulate it in the framework of the program for tracing particles in the experimental setup. One of the most popular such programs is Geant4. Specifically, the package includes the processes of DM particles production via electron and muon bremsstrahlung off nuclei, resonant in-flight positron annihilation on atomic electrons and gamma to ALP (axion-like particles) conversion on nuclei. Four types of DM mediator particles are considered: vector, scalar, pseudoscalar and axial vector. In particular, for bremsstrahlung the total cross sections are calculated at exact tree level (ETL). The code handles both the case of invisible DM mediator decay and of visible decay into $e^+e^-$ (or into $\gamma \gamma$ in the case of ALP). The software consists of a collection of different classes, inheriting from the Geant4 framework classes, thus the expected use of this package is to include it in a Geant4-based code for the simulation of particles propagation and interaction in the detector. As an example of its usage, we discuss the results obtained from the simulation of a typical active beam-dump experiment, considering $5 \times 10^{12}$ 100 GeV electrons impinging on a lead/plastic scintillator active thick target, showing the expected sensitivity for the four types of DM mediator particles mentioned above.