structural:expansion
Fields

Quarks are massive spin- 1 ⁄ 2 fermions that carry a color charge whose gauging is the content of QCD. Quarks are represented by Dirac fields in the fundamental representation 3 of the gauge group SU(3). They also carry electric charge (either − 1 ⁄ 3 or + 2 ⁄ 3) and participate in weak interactions as part of weak isospin doublets. They carry global quantum numbers including the baryon number, which is 1 ⁄ 3 for each quark, hypercharge and one of the flavor quantum numbers.

Gluons are spin-1 bosons that also carry color charges, since they lie in the adjoint representation 8 of SU(3). They have no electric charge, do not participate in the weak interactions, and have no flavor. They lie in the singlet representation 1 of all these symmetry groups.

Each type of quark has a corresponding antiquark, of which the charge is exactly opposite. They transform in the conjugate representation to quarks, denoted 3 ¯ {\displaystyle {\bar {\mathbf {3} }}}.