YukawaKopplung

Yukawa Kopplung refers to a type of interaction in quantum field theory that describes the coupling between a fermion field and a scalar or pseudoscalar meson field. This interaction is named after the Japanese physicist Hideki Yukawa, who first proposed it in 1935 to explain the strong nuclear force. In his original work, Yukawa theorized that the force between nucleons (protons and neutrons) was mediated by the exchange of a hypothetical particle, which he called a meson.

The Yukawa potential, derived from this theory, describes the force between two particles as being proportional to a decaying exponential function of the distance between them. This form of potential is characteristic of forces mediated by massive particles, such as mesons, where the range of the force is inversely proportional to the mass of the mediating particle. The strength of the interaction is determined by a coupling constant, often denoted by 'g'.

Mathematically, the Yukawa coupling term in a Lagrangian density is typically written as $g \bar{\psi} \phi \psi$ for a scalar field $\phi$ or $g \bar{\psi} i \gamma^5 \phi \psi$ for a pseudoscalar field $\phi$, where $\psi$ represents the fermion field and $\bar{\psi}$ is its Dirac adjoint. This term signifies that the fermion field interacts with the meson field, leading to processes like meson emission or absorption by fermions.

The concept of Yukawa coupling has been crucial in developing the Standard Model of particle physics. While the strong nuclear force between nucleons is now primarily described by quantum chromodynamics (QCD) involving quarks and gluons, the Yukawa coupling remains fundamental for describing the interaction of quarks and leptons with the Higgs boson, which is a scalar field. This interaction is responsible for giving mass to elementary particles. The strength of these couplings dictates the masses of the respective fermions.