Gauge boson certain atoms. The Standard Model of particle physics recognizes four kinds of gauge bosons: photons, which carry the electromagnetic interaction; W and Z bosons, which carry the weak interaction; and gluons, which carry the strong interaction. Isolated gluons do not occur because they are color-charged and subject to color confinement. In a quantized gauge theory, gauge bosons are quanta of the gauge fields. Consequently, there are as many gauge bosons as there are generators of the gauge field. In quantum electrodynamics, the gauge group is "U"(1); in this simple case, there is only one gauge boson. In quantum chromodynamics, the
Gauge theory Lagrangian. In the quantized version of the obtained classical field theory, the quanta of the gauge field "A"("x") are called gauge bosons. The interpretation of the interaction Lagrangian in quantum field theory is of scalar bosons interacting by the exchange of these gauge bosons. The picture of a classical gauge theory developed in the previous section is almost complete, except for the fact that to define the covariant derivatives "D", one needs to know the value of the gauge field formula_29 at all space-time points. Instead of manually specifying the values of this field, it can be given as the