" All of these theories are gauge theories, meaning that they model the forces between fermions by coupling them to bosons which mediate (or "carry") the forces. The Lagrangian of each set of mediating bosons is invariant under a transformation called a gauge transformation, so these mediating bosons are referred to as gauge bosons . The bosons in the Standard Model are: Unsolved problems in physics: Parameters in the Standard Model: What gives rise to the Standard Model of particle physics? Why do its particle masses and coupling constants possess the values we have measured? Does the Higgs boson predicted by the model really exist? Why are there three generations of particles in the Standard Model? Is the Standard Model reality, a good approximation to reality, or fatally flawed? Photons, which mediate the electromagnetic interaction. W and Z bosons, which mediate the weak nuclear force Eight species of gluons, which mediate the strong nuclear force. Six of these gluons are labelled as pairs of "colors" and "anti-colors" (for example, a gluon can carry "red" and "anti-green". ) The other two species are a more complex mix of colors and anti-colors. The Higgs bosons, which induce spontaneous symmetry breaking of the gauge groups and are responsible for the existence of inertial mass. Hot Teenage Model It turns out that the gauge transformations of the gauge bosons can be exactly described using a unitary group called a "gauge group". The gauge group of the strong interaction is SU(3), and the gauge group of the electroweak interaction is SU(2)×U(1). "

" Rev. Lett. 83, 1529 (1999). S. F. Novaes, Standard Model: An Introduction, hep-ph:0001283 I. Models are usually man-constituted. Model Hot Air Balloon That justifies talking about their purpose prior to talking about their consistency. Models are used as substitutes for originals because properties of the latter are of interest and the originals are not going to be investigated themselves. "