What are gleons and quarks?

Gleons are hypothetical particles that are proposed in some theories of particle physics, particularly in the context of quantum gravity and string theory, where they are thought to mediate the interactions between strings. Quarks, on the other hand, are elementary particles and fundamental constituents of matter, combining to form protons and neutrons, which make up atomic nuclei. Quarks come in six types (flavors) and are held together by the strong force, mediated by particles called gluons. While quarks have been experimentally confirmed, gleons remain speculative and have not been observed.