Quantum chromodynamics is the theoretical frame work in which one
can treat the physics of the strong interactions. This is the non-abelian gauge field
theory, and it cannot be solved in the perturbation theory since the free Lagrangian
densities of quarks and gluons are not gauge invariant. In the perturbation theory,
we describe all the physical observables in terms of the properties of quarks and
gluons, and if they are not related to physical observables, then there is no point
of employing the perturbation theory. Here, we also discuss the nucleon-nucleon
interactions based on the meson exchange processes and present the calculation of
the two pion exchange potential. Further, we discuss some physical observables in
connection with quarks, that is, the magnetic moments of nucleons in terms of quark
model and the total cross section ratio between σe+e-→ hadrons and σe+e-→μ+μ-.
These physical quantities are related to the quark degrees of freedom.
Keywords: Hamiltonian of QCD, color charge, nuclear force, two pion exchange, quark
model prediction of nucleon magnetic moments.
