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This mixing explains how electromagnetic and weak forces are related.<ref name="weinberg"/>
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== Spontaneous symmetry breaking ==
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==References==
= References =
{{reflist|3}}
{{reflist|3}}
{{Author|Harold Foppele}}
{{Author|Harold Foppele}}


{{Sourceattribution|Physics:Quantum Electroweak theory|1}}
{{Sourceattribution|Physics:Quantum Electroweak theory|1}}

Latest revision as of 00:31, 24 May 2026

← Back to Quantum field theory Book I
← Previous : Chromodynamics (QCD)
Next : Standard Model →

Electroweak theory it forms a central part of the Standard Model of particle physics. It forms a central part of the Standard Model of particle physics. Electroweak theory shows that the electromagnetic force and weak nuclear force are different manifestations of a single interaction at high energies. At high energies, they merge into a unified electroweak interaction. The theory is based on the symmetry group: Gauge fields are introduced to preserve local symmetry, leading to four gauge bosons. The electroweak theory predicts four gauge bosons: These combine to form the physical particles: This mixing explains how electromagnetic and weak forces are related. The electroweak symmetry is not directly observed because it is spontaneously broken.

Quantum Electroweak theory.

Unification of forces

Electroweak theory shows that the electromagnetic force and weak nuclear force are different manifestations of a single interaction at high energies.

At low energies:

  • electromagnetic interaction → long-range force
  • weak interaction → short-range force

At high energies, they merge into a unified electroweak interaction.[1]

Gauge symmetry

The theory is based on the symmetry group: SU(2)L×U(1)Y

where:

  • SU(2)L acts on left-handed fermions
  • U(1)Y corresponds to weak hypercharge

Gauge fields are introduced to preserve local symmetry, leading to four gauge bosons.[2]

Gauge bosons

The electroweak theory predicts four gauge bosons:

  • Wμ1,Wμ2,Wμ3 (from SU(2))
  • Bμ (from U(1))

These combine to form the physical particles:

  • W+ and W− (charged weak bosons)
  • Z0 (neutral weak boson)
  • γ (photon)

This mixing explains how electromagnetic and weak forces are related.[3]

Spontaneous symmetry breaking

The electroweak symmetry is not directly observed because it is spontaneously broken.

This occurs through the Higgs mechanism, introducing a scalar field whose vacuum expectation value selects a specific ground state: ⟨ϕ⟩≠0

As a result:

  • W± and Z0 acquire mass
  • the photon remains massless

This explains the short range of the weak interaction.[4]

Electroweak Lagrangian

The electroweak Lagrangian includes:

  • fermion kinetic terms
  • gauge field terms
  • Higgs field contributions
  • interaction terms

These components together describe the full dynamics of the electroweak interaction.

Weak interactions

The weak interaction involves processes such as:

  • beta decay
  • neutrino interactions
  • flavor-changing processes

These are mediated by the W± and Z0 bosons.

Experimental confirmation

Electroweak theory has been confirmed by numerous experiments, including:

  • discovery of the W and Z bosons
  • precision measurements at particle accelerators
  • observation of the Higgs boson

These results strongly support the validity of the theory.[2]

Role in the Standard Model

Electroweak theory, together with quantum chromodynamics, forms the core of the Standard Model.

It unifies two of the fundamental forces and provides a consistent framework for describing particle interactions.

Conceptual importance

Electroweak theory demonstrates how gauge symmetry and spontaneous symmetry breaking combine to produce realistic physical theories.

It is a cornerstone of modern particle physics and a key step toward deeper unification.

See also

Table of contents (217 articles)

Index

Full contents

References

  1. ↑ Peskin, M. E.; Schroeder, D. V. An Introduction to Quantum Field Theory (1995).
  2. ↑ 2.0 2.1 Schwartz, M. D. Quantum Field Theory and the Standard Model (2014).
  3. ↑ Weinberg, S. (1967). A model of leptons.
  4. ↑ Higgs, P. W. (1964). Broken symmetries and the masses of gauge bosons.
Author: Harold Foppele


Source attribution: Physics:Quantum Electroweak theory

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