QCD and Asymptotic Freedom
In non-Abelian gauge theories, the beta function can be negative, as first found by Frank Wilczek, David Politzer and David Gross. An example of this is the beta function for Quantum Chromodynamics (QCD), and as a result the QCD coupling decreases at high energies.
Furthermore, the coupling decreases logarithmically, a phenomenon known as asymptotic freedom (the discovery of which was awarded with the Nobel Prize in Physics in 2004). The coupling decreases approximately as
where β0 is a constant computed by Wilczek, Gross and Politzer.
Conversely, the coupling increases with decreasing energy. This means that the coupling becomes large at low energies, and one can no longer rely on perturbation theory.
Read more about this topic: Coupling Constant
Famous quotes containing the word freedom:
“The free man is a warrior.—How is freedom measured among individuals, among peoples? According to the resistance that must be overcome, according to the trouble it takes to stay on top. The highest type of free man must be sought where the highest resistance is constantly overcome: five steps away from tyranny, close to the threshold of the danger of servitude.”
—Friedrich Nietzsche (1844–1900)