Asymptotic freedom is a phenomenon in quantum chromodynamics (QCD), the theory describing the strong nuclear force, which governs the interactions between quarks and gluons. It was discovered by physicists David Gross, Frank Wilczek, and David Politzer in the early 1970s and earned them the Nobel Prize in Physics in 2004.
In quantum chromodynamics, quarks and gluons are the fundamental particles that make up protons, neutrons, and other hadrons. The strong force between them is mediated by gluons, which are the carriers of the force. Unlike the electromagnetic force, which becomes weaker as particles move farther apart, the strong force becomes stronger at short distances (high energies). This behavior is known as the phenomenon of confinement, where quarks and gluons are tightly bound within particles and cannot be observed as isolated entities.
However, at high energies or very short distances, a surprising phenomenon occurs in QCD known as asymptotic freedom. It describes the behavior of the strong force when particles are close together or at high energies. Asymptotic freedom implies that at very short distances or very high energies, the strong force weakens and approaches zero. In other words, the quarks and gluons become effectively "free" and interact weakly with each other.
Asymptotic freedom arises due to the peculiar way the strong force interacts with itself. In QCD, the gluons can interact with other gluons, resulting in a complex web of interactions. This behavior leads to a cancellation of the attractive forces between quarks and gluons, and at high energies, the net effect is a weakening of the overall force.
The phenomenon of asymptotic freedom is derived mathematically through a quantum field theory technique called renormalization group analysis. This approach allows physicists to study how the strength of the strong force changes as the energy scale or distance scale is varied. The calculations predict that at very short distances or high energies, the strong force becomes weaker, leading to the phenomenon of asymptotic freedom.
Asymptotic freedom has important consequences for the behavior of quarks and gluons in high-energy particle interactions. It helps explain phenomena observed in particle accelerators, such as the deep inelastic scattering experiments, where the scattering of electrons off protons revealed the point-like nature of quarks and provided evidence for the existence of asymptotic freedom in QCD.