General properties of the decay amplitudes for massless particles

TL;DR

This paper derives kinematic constraints for massless particle decays and shows that photons, Yang-Mills bosons, and gravitons do not decay under certain conditions, highlighting the role of self-couplings in decay processes.

Contribution

It provides a comprehensive analysis of decay amplitudes for massless particles and establishes conditions under which such particles can decay.

Findings

Photon and Yang-Mills boson decay probabilities vanish to all orders.

Graviton decay probability vanishes at one-loop and all orders for matter loops.

Decay requires a non-derivative self-coupling with positive mass dimension.

Abstract

We derive the kinematical constraints which characterize the decay of any massless particle in flat spacetime. We show that in perturbation theory the decay probabilities of photons and Yang-Mills bosons vanish to all orders; the decay probability of the graviton 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.