Coupling constant

In a gauge theory in quantum field theory, a coupling constant (coupling or gauge coupling constant) is a number representing the strength of a force involved in a physical interaction. The fine-structure constant is perhaps the most important coupling constant in physics. In nuclear chemistry and nuclear physics, J-coupling measures, directly in hertz (Hz), the strength of interaction between adjacent atoms.

Quotes

• That the pion-nucleon (πN) coupling constant is fundamental in our understanding of the Cosmos has been adequately emphasised in numerous works. In meson-exchange models of the strong interaction, a significantly weaker coupling between the pions and the nucleons would have prevented the neutrons from combining fast with protons in the early Universe; they would have decayed before they had any chance to be enmeshed first in deuterons, then in other light nuclei. According to the Big-Bang Nucleosynthesis, within half an hour of the Big Bang, all existing matter had assumed the form of free electrons, protons, and helium nuclei (as well as traces of other nuclei up to ⁷Be). On the contrary, a significantly stronger coupling would have resulted in the rapid creation of bound diprotons and would have led to a helium-dominated Universe. It is hard to imagine how life could emerge in such a Universe: typical stars burn hydrogen to helium for about 90 % of their lives.
  • Evangelos Matsinos, "A brief history of the pion-nucleon coupling constant". arXiv:1901.01204v2 [nucl-th]. DOI:10.48550/arXiv.1901.01204. (quote from pp. 1–2)

• ... Roughly speaking, in renormalizable theories no coupling constants can have the dimensions of negative powers of mass. But every time we add a field or a space-time derivative to an interaction, we reduce the dimensionality of the associated coupling constant. So only a few simple types of interaction can be renormalizable. ...
  • Steven Weinberg, "Conceptual Foundations of the Unified Theory of Weak and Electromagnetic Interactions; Nobel Lecture, December 8, 1979". Nobel Lectures, Physics 1971-1980. Singapore: World Scientific Publishing Company. 1992. pp. 543–559.  (quote from pp. 546–547; edited by Stig Lundqvist)

External links

Encyclopedic article on Coupling constant on Wikipedia