Massless particles, such as photons and gluons, move with the speed of light and consequently experience no time. According to Special Relativity, time stops at the speed of light. As a result, massless particles exist in the same moment of their proper time from the emission to absorption. Therefore massless particles cannot decay or experience any other change. A practical example of this logic is that neutrinos have mass, because massless neutrinos cannot oscillate.
It seems that two massless particles that don't experience time should not be able to interact with each other (at least without the interaction mediated by virtual massive particles). This holds true for photons not interacting with each other (in the first order) resulting in the linearity of the electromagnetic field.
QCD is a non-linear theory with gluons interacting with each other via 3 and 4 vertices. Specifically the 3-gluon vertex (please correct me if I am wrong) under specific conditions can be viewed as a gluon decay into two gluons. However, massless particles cannot decay according to Special Relativity. What is the explanation of why massless gluons can interact with each other and apparently even decay while not experiencing time?