Yukawa interaction

A quantum-field interaction coupling a scalar field to fermion fields through a dimensionless coupling constant. It can generate fermion masses when the scalar field has a nonzero vacuum expectation value.

Yukawa coupling: A parameter measuring the strength of a Yukawa interaction between scalar and fermion fields. Its value sets the strength of each fermion’s coupling to the scalar field.
Scalar field: A field whose value is unchanged by spatial rotations of the coordinate system. It supplies the bosonic field in the interaction.
Higgs boson: The spin-zero particle associated with the Higgs field and discovered at CERN in 2012. Its interactions with fermions measure their Yukawa couplings.
Hideki Yukawa: A Japanese theoretical physicist who proposed the meson theory of nuclear forces and received the 1949 Nobel Prize in Physics. The interaction is named for Yukawa, although his nuclear-force theory concerned mesons.
Flavor problem: The unresolved question of why fermion masses and flavor-mixing parameters have their observed values. Yukawa couplings encode the unexplained values and hierarchy of fermion masses.
Higgs mechanism: A process in which spontaneous symmetry breaking gives masses to gauge bosons and fermions while preserving gauge invariance. The Higgs field’s vacuum value turns Yukawa couplings into fermion masses.
Fermion: A particle or field with half-integer spin that obeys Fermi–Dirac statistics. Fermion fields provide the matter degrees of freedom coupled by the interaction.
Fermion mass: The inertial mass associated with a fermion field or particle. In the Standard Model, fermion masses arise from Yukawa couplings after Higgs symmetry breaking.
Meson theory of nuclear forces: Yukawa’s proposal that nuclear forces arise through the exchange of massive mesons. The historical name comes from this theory, not from the modern Higgs–fermion coupling.
Neutrino oscillation: The quantum-mechanical change of a neutrino’s flavor as it propagates, caused by differences among neutrino masses. Oscillations establish neutrino mass, whose Yukawa origin is unknown.

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