Quantum chromodynamics is the theory of strong interactions from "summary" of The Quantum Theory of Fields by Steven Weinberg,Weinberg S
In the theory of strong interactions, the basic constituents of matter, quarks, are held together by the exchange of particles called gluons. The theory that describes the strong interactions of quarks and gluons is called quantum chromodynamics (QCD). Unlike the electromagnetic force, which weakens as charged particles move farther apart, the strong force remains constant over large distances. This is due to the fact that the force between quarks does not decrease with distance, but rather increases. The strength of the strong force is described by a parameter called the coupling constant, which measures how strongly quarks interact with each other through the exchange of gluons. At short distances, the coupling constant is small, allowing perturbation theory to be used to make precise calculations of strong interaction processes. However, at large distances, the coupling constant becomes large, leading to the phenomenon of confinement, where quarks are never found in isolation but are always bound together in composite particles such as protons and neutrons. One of the key features of QCD is asymptotic freedom, which means that at very short distances, quarks and gluons behave as free particles that do not interact strongly with each other. This property was discovered by Gross, Wilczek, and Politzer, and earned them the Nobel Prize in Physics in 2004. Asymptotic freedom is essential for understanding the behavior of quarks and gluons in high-energy collisions, such as those produced in particle accelerators like the Large Hadron Collider. The development of QCD has led to a deeper understanding of the strong force and its role in shaping the structure of matter. By studying the dynamics of quarks and gluons within the framework of QCD, physicists have been able to make precise predictions for a wide range of strong interaction processes, from the behavior of protons and neutrons to the production of exotic particles in high-energy collisions. Quantum chromodynamics stands as a cornerstone of the Standard Model of particle physics, providing a comprehensive description of the interactions between the fundamental particles of the universe.
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