Strong Interactions $\equiv 3$

The theory of the strong interactions between quarks and gluons is quantum chromodynamics (QCD) which is the gauge theory based on the $SU(3)_{C}$ group of colour. This theory is a descendant from:

- Parton model: coming from the scale invariance of the deep inelastic scattering.

- Quark model: coming from $SU(3)_{f}$ of flavour and hadronic spectroscopy that united to the previous one provides the quark-parton model.

- Hypothesis of colour: appearing to solve several problems of the quark parton model as :i) Fermi Dirac statistics; ii) Experimental data; iii) Renormalizability of the theory $SU(2) \times U(1)$ (ABJ anomaly).

To the colour hypothesis which implies a degree of freedom to be placed in the $SU(3)_{C}$ group of colour underlies the confinement hypohtesis: to admit that hadrons are white (singlets of colour).