# How do we know that gluons have no electric charge?

Since the W boson carries electric charge and there is no a priori reason that massless electrically charged bosons cannot exist, I'm wondering if the lack of gluon electric charge has been confirmed experimentally or there exists a compelling theoretical reason that they cannot carry electric charge.

In particular, there seems no reason that the 6 non-diagonal gluons can't carry +-1 electric charge if we establish a cyclic quasiordering of colors and if we assume the number of gluons with positive charge are equal to those with negative charge.

Just as the total color charge of a baryon remains the same although quarks are constantly emitting and absorbing color charge via gluons, why not the same for electric charge or, in other words, isospin?

• What is a cyclic quasiordering? – G. Smith Mar 27 '19 at 16:38
• But that'd mean when a quark emits a charged gluon its charge would change without its flavour changing. – PM 2Ring Mar 27 '19 at 16:38
• If there was a massless, charged particle coupling to the strong force, wouldn't we then have decays like ${}^{137}\text{Cs}\rightarrow{}^{137}\text{Ba}+\text{g}$? – user4552 Mar 27 '19 at 16:54
• @BenCrowell Aren't single gluons confined by the strong interaction just like quarks are? It doesn't seem like this would change if they had electric charge, because the strong interaction would dominate. – G. Smith Mar 27 '19 at 20:39
• @G.Smith: Yeah, I'm uncertain about that, and that's why I posted it as a comment rather than an answer. But I think the decay might still happen, and you would just see a jet rather than the gluon itself. – user4552 Mar 28 '19 at 13:34