General properties of the decay amplitudes for massless particles

We derive the kinematical constraints which characterize the decay of any massless particle in flat space-time. We show that in perturbation theory the decay probabilities of photons and Yang-Mills bosons vanish to all orders and the decay probability of gravitons vanishes to one-loop order for graviton loops and to all orders for matter loops. A general power counting argument indicates in which conditions a decay of a massless particle could be possible: the Lagrangian should contain a self-coupling without derivatives and with a coupling constant of positive mass dimension.