This page is about the notion in physics/quantum field theory. For the concept of “coupling” in probability theory, see transport plan.
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In the Lagrangian of a prequantum field theory the those terms that involve various fields describe the coupling or interaction of these fields with each other. Hence the prefactors of these terms encode the strength of this coupling, and hence are called coupling constants.
In perturbative quantum field theory the coupling constant (as well as Planck's constant which indicates the strength of quantum effects) is regarded as tiny, in fact as infinitesimal, in that all observables are expressed as (generally non-converging, asymptotic) formal power series in the coupling constant.
Beyond that approximation, in the realm of finite (large) coupling, one speaks of non-perturbative field theory.
See also
Last revised on January 26, 2024 at 09:31:51. See the history of this page for a list of all contributions to it.