This task is for implementing tau decays in EvtGen using the Helicity Matrix Element (HME) decay amplitude model in Pythia, which keeps particle spin information. We can then remove all TAUOLA-based code.
Code development should use the tauPythia branch. The decay model is called EvtHmePythia which uses the EvtPythiaEngine, both defined in the EvtGenExternal source and header file directories.
The EvtPythiaEngine::hmeAmplitudes() method needs the initWaves() function in pythia8/include/Pythia8/HelicityMatrixElements.hto be made public (instead of being protected).