# Perturbative QCD

Perturbative QCD is a subfield of particle physics in which the theory of strong interactions, Quantum Chromodynamics (QCD), is studied by using the fact that the strong coupling constant $\alpha_s$ is small in high energy or short distance interactions, thus allowing Perturbation theory techniques to be applied. In most circumstances, making testable predictions with QCD is extremely difficult, due to the infinite number of topologically inequivalent interactions possible. Over short distances, the coupling is small enough that this infinite number of terms can be approximated accurately by a much more manageable number of terms. Although limited in scope, this approach has resulted in the most precise tests of QCD to date.