Self-annihilation of the neutralino dark matter into two photons or a Z and a photon in the MSSM

We revisit the one-loop calculation of the annihilation of a pair of the lightest neutralinos into a pair of photons, a pair of gluons and also a Z photon final state. For the latter we have identified a new contribution that may not always be negligible. For all three processes we have conducted a tuned comparison with previous calculations for some characteristic scenarios. The approach to the very heavy higgsino and wino is studied and we argue how the full one-loop calculation should be matched into a more complete treatment that was presented recently for these extreme regimes. We also give a short description of the code that we exploited for the automatic calculation of one-loop cross sections in the MSSM that could apply both for observables at the colliders and for astrophysics or relic density calculations. In particular the automatic treatment of zero Gram determinants which appear in the latter applications is outlined. We also point out how generalised non-linear gauge fixing constraints can be exploited.Comment: 20 pages, 5 figure