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Hence, the actual value of the coupling constant is only defined at a given energy scale. In QCD, the Z boson mass scale is typically chosen, providing a value of the strong coupling constant of α s (M Z 2) = 0.1179 ± 0.0010. [7] In 2023 Atlas measured α s (M Z 2) = 0.1183 ± 0.0009 the most precise so far.
The second term is the CP violating θ-term, with the strong coupling constant, the gluon field strength tensor, and ~ the dual field strength tensor. The third term is known as the color anomaly , a consequence of the Peccei–Quinn symmetry being anomalous, with ξ {\displaystyle \xi } determined by the choice of PQ charges for the quarks.
Most evidence points to a moderately large coupling, typically of value 1-3 [7] depending on the choice of renormalization scheme. In contrast to the simple but erroneous mechanism of infrared slavery , a large coupling is but one ingredient for color confinement, the other one being that gluons are color-charged and can therefore collapse into ...
In addition to the ordering scheme, most terms in the approximate Lagrangian will be multiplied by coupling constants which represent the relative strengths of the force represented by each term. Values of these constants – also called low-energy constants or Ls – are usually not known. The constants can be determined by fitting to ...
The strong coupling constant is conventionally labelled g s (or simply g where there is no ambiguity). The observations leading to the discovery of this part of the Standard Model are discussed in the article in quantum chromodynamics.
In quantum field theory and string theory, a coupling constant is a number that controls the strength of interactions in the theory. For example, the strength of gravity is described by a number called Newton's constant, which appears in Newton's law of gravity and also in the equations of Albert Einstein's general theory of relativity.
In particle physics, Yukawa's interaction or Yukawa coupling, named after Hideki Yukawa, is an interaction between particles according to the Yukawa potential. Specifically, it is between a scalar field (or pseudoscalar field) ϕ {\displaystyle \ \phi \ } and a Dirac field ψ {\displaystyle \ \psi \ } of the type
The word strong is used since the strong interaction is the "strongest" of the four fundamental forces. At a distance of 10 −15 m, its strength is around 100 times that of the electromagnetic force , some 10 6 times as great as that of the weak force, and about 10 38 times that of gravitation .