electroweak

Electroweak theory is the part of the Standard Model of particle physics that unifies the electromagnetic and weak nuclear forces into a single framework. It is described as a gauge theory with the symmetry group SU(2)L × U(1)Y and is mediated by the gauge bosons W+, W−, Z0 and the photon. The theory was developed in the 1960s by Sheldon Glashow, Abdus Salam, and Steven Weinberg and has since become a central pillar of particle physics, explaining how two seemingly different forces arise from a common origin at high energies.

Spontaneous symmetry breaking, via the Higgs field, gives mass to the W± and Z0 bosons while keeping the photon massless. The same mechanism generates masses for fermions through Yukawa couplings. The electroweak sector is renormalizable and makes precise predictions for interaction strengths and particle masses, which can be tested against experimental data. The weak mixing angle, commonly denoted θW, relates the couplings of the photon and the Z boson to fermions.

Experimental evidence for the electroweak theory includes the observation of W and Z bosons, neutral current interactions, and a set of precision measurements from LEP, SLC, the Tevatron, and the Large Hadron Collider. The discovery of the Higgs boson in 2012 with a mass around 125 GeV confirmed the mechanism of electroweak symmetry breaking. Relationships such as mW = mZ cos θW and the measured value of sin^2θW are continually refined by data and remain consistent with the Standard Model predictions.

Within the Standard Model, the electroweak theory is combined with quantum chromodynamics to form the full gauge structure SU(3)c × SU(2)L × U(1)Y. While highly successful, it does not incorporate gravity and points toward physics beyond the Standard Model for phenomena such as neutrino masses and matter–antimatter asymmetry.