Gluones

Gluones, the Spanish plural form of gluón, refer to the gauge bosons of quantum chromodynamics (QCD), the theory of the strong interaction. They are the force carriers that mediate interactions between quarks and bind them into hadrons such as protons, neutrons, and mesons. Like photons in electromagnetism, gluones are quanta of a field, but they carry color charge themselves.

Gluones are massless, have spin 1, and carry color charge belonging to the adjoint representation of SU(3). There are eight independent gluones corresponding to the eight generators of the SU(3) gauge symmetry. Unlike photons, gluones interact with each other, a feature of non-Abelian gauge theories, which gives rise to properties such as confinement and asymptotic freedom.

They couple to quarks with a strength governed by the strong coupling constant αs, which decreases at high energies (asymptotic freedom) and increases at low energies, leading to confinement. In high-energy collisions, gluones can be radiated by quarks, and multiple gluons may participate in parton showers, resulting in hadronization and jets observed in detectors. Gluones cannot be isolated under normal conditions; they exist within color-neutral bound states.

Experimental evidence for gluones includes three-jet events in electron–positron annihilation, first observed in the late 1970s, and later studies confirming gluon bremsstrahlung and jet structure in various processes. The existence of bound gluon states, or glueballs, is predicted by QCD, though definitive identification remains challenging. Gluones are a central component of the Standard Model's description of the strong force.