| Brout–Englert–Higgs mechanism | |
|---|---|
| Name | Brout–Englert–Higgs mechanism |
| Field | Particle physics |
| Discovered | 1964 |
| Discoverers | François Englert; Robert Brout; Peter Higgs |
| Notable predictions | Higgs boson |
| Institutions | CERN; University of Brussels; University of Edinburgh |
Brout–Englert–Higgs mechanism
The Brout–Englert–Higgs mechanism is a fundamental process in Quantum field theory that explains how elementary particles acquire mass via interaction with a pervasive scalar field. It underpins the mass generation of the W and Z bosons in the electroweak interaction and predicts the existence of the Higgs boson, a key component of the Standard Model. The mechanism is central to modern particle physics and has profound consequences for cosmology and unified theories.
The mechanism was independently proposed in 1964 by Robert Brout and François Englert and shortly thereafter by Peter Higgs, with related work by Gerald Guralnik, C. R. Hagen, and Tom Kibble. It addressed the longstanding problem of how gauge bosons could be massive without violating gauge invariance and renormalizability established by Richard Feynman and formalized in perturbative QED and later QCD. The concept fit into the emerging framework of the Glashow–Weinberg–Salam model of electroweak unification developed by Sheldon Glashow, Steven Weinberg, and Abdus Salam. Acceptance grew through theoretical work on spontaneous symmetry breaking led by studies in condensed matter physics, notably analogies with the Meissner effect in superconductivity and the role of the Goldstone theorem resolved by the mechanism.
Within Quantum field theory, the Brout–Englert–Higgs mechanism uses a scalar field with a nonzero vacuum expectation value to break a continuous gauge symmetry spontaneously while preserving local gauge invariance. The formalism employs Lagrangian methods developed by Paul Dirac and others, canonical quantization, and path-integral techniques popularized by Julian Schwinger and Richard Feynman. Crucial mathematical results on renormalization from Gerard 't Hooft and Martinus Veltman established that gauge theories with spontaneous symmetry breaking remain renormalizable, legitimizing incorporation into the Standard Model of particle physics.
Spontaneous symmetry breaking occurs when the ground state of a system does not share the symmetry of its Lagrangian. The Higgs field is a complex scalar doublet in the minimal model, the Standard Model Higgs field, whose potential leads to degenerate minima. Selecting one vacuum breaks the SU(2)×U(1) electroweak symmetry down to U(1) and gives mass to gauge bosons while "eating" would-be Nambu–Goldstone boson modes. The interplay of symmetry, vacuum structure, and gauge transformations is informed by group theory and representations as used in Lie group analyses.
In the minimal scheme, three degrees of freedom from the Higgs doublet provide longitudinal polarizations for the charged and neutral weak bosons, producing masses for the W boson and Z boson while leaving the photon massless. Fermion masses arise through gauge-invariant Yukawa couplings between the Higgs field and matter fields, with coupling constants fixed to experimental fermion masses for quarks and leptons in the CKM and PMNS contexts. The mechanism preserves the renormalizability of the Glashow–Weinberg–Salam model and is consistent with precision tests performed at LEP and the Tevatron.
Experimental confirmation culminated with the 2012 discovery of a Higgs-like boson by the ATLAS experiment and CMS experiment at the Large Hadron Collider (LHC) at CERN. The observed particle's properties—mass near 125 GeV, spin-parity consistent with 0+ and couplings to W bosons, Z bosons, fermions, and photons via loop processes—matched predictions of the minimal Higgs sector. Earlier indirect evidence included electroweak precision measurements at SLAC and CERN's LEP collider that constrained the Higgs mass range via radiative corrections. The 2013 and 2014 awards of the Nobel Prize in Physics to Englert and Higgs recognized the theoretical insight; Brout had died in 2011.
The canonical Lagrangian contains kinetic terms, gauge interactions, and a scalar potential V(φ) = μ^2|φ|^2 + λ|φ|^4. Variants extend the minimal model: the Two-Higgs-doublet model (2HDM), supersymmetric realizations such as the Minimal Supersymmetric Standard Model (MSSM), and composite-Higgs models motivated by strong dynamics like technicolor. Effective field theory methods, especially SMEFT, parameterize deviations from the minimal Higgs sector relevant to LHC searches. Nonperturbative studies use lattice techniques analogous to those in Lattice QCD to explore strong-coupling regimes.
The mechanism is integral to the consistency and predictive power of the Standard Model, affecting flavour physics, electroweak baryogenesis scenarios, and vacuum stability analyses that involve the top quark mass and Higgs self-coupling. Cosmological implications include roles in inflation-adjacent models, phase transitions in the early Universe, and potential connections to dark matter candidates in extended sectors. Outstanding questions—naturalness and the hierarchy problem—motivate searches for physics beyond the Standard Model at CERN's LHC, future colliders like the proposed International Linear Collider and theoretical frameworks such as GUTs and supersymmetry.
Category:Quantum field theory Category:Particle physics Category:Higgs boson