Physics:Quantum Standard Model
The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetic, weak and strong interactions – excluding gravity) in the universe and classifying all known elementary particles.
It was developed in stages throughout the latter half of the 20th century, through the work of many scientists worldwide,[1] with the current formulation finalized in the mid-1970s upon experimental confirmation of the existence of quarks.
The Standard Model is a paradigm of a quantum field theory, exhibiting phenomena such as spontaneous symmetry breaking, anomalies, and renormalization.[2]
Gauge structure
The Standard Model is defined by the gauge symmetry:
which corresponds to:
This symmetry determines the allowed interactions and particle content.[3]
Particle content
All particles can be classified into fermions and bosons.
Fermions
The Standard Model includes 12 fermions of spin , grouped into three generations.[4]
- Quarks: up, down, charm, strange, top, bottom
- Leptons: electron, muon, tau and their neutrinos
Quarks carry color charge and participate in the strong interaction, while leptons do not.
Fermions obey the Pauli exclusion principle and constitute all ordinary matter.[5]
Gauge bosons
Gauge bosons mediate the fundamental interactions:
- Photon → electromagnetic force
- Gluons → strong interaction
- W and Z bosons → weak interaction
These arise from the gauge symmetry of the theory and act as force carriers.[6]
Higgs boson
The Higgs boson is a scalar particle responsible for mass generation via the Higgs mechanism.[7][8][9]
The Higgs field acquires a vacuum expectation value:
which leads to:
- masses for W and Z bosons
- masses for fermions
- a massless photon
Lagrangian structure
The Standard Model is formulated as a quantum field theory with a Lagrangian composed of several sectors:
- Quantum chromodynamics (QCD)
- Electroweak sector
- Higgs sector
- Yukawa interactions
Each sector respects gauge invariance and contributes to the dynamics of particles and interactions.[10]
Fundamental interactions
The Standard Model describes three fundamental interactions:
- Electromagnetism
- Weak interaction
- Strong interaction
These interactions arise from the exchange of gauge bosons between particles.[11]
Gravity is not included due to incompatibility with quantum field theory.[12]
Experimental confirmation
The Standard Model has been confirmed by numerous experiments, including:
- discovery of quarks
- observation of W and Z bosons
- discovery of the Higgs boson (2012)[13]
Its predictions agree with experimental data to high precision.[14]
Limitations
Despite its success, the Standard Model is incomplete:
- does not include gravity
- does not explain dark matter or dark energy
- does not explain matter–antimatter asymmetry
- originally did not include neutrino masses
These issues motivate theories beyond the Standard Model.[15][16]
Historical development
The development of the Standard Model involved key contributions:
- Dirac equation (1928) introducing antimatter[17]
- Yang–Mills theory (1954) extending gauge symmetry[3]
- Electroweak unification (Glashow, Weinberg, Salam)[18][19]
- Introduction of quarks (Gell-Mann, Zweig)[20]
- Higgs mechanism (1964)[7]
- Asymptotic freedom in QCD (1973)[21][22]
These developments established the modern framework of particle physics.
Conceptual role
The Standard Model represents the culmination of:
- gauge symmetry principles
- non-Abelian gauge theory
- quantum field theory
It unifies QED, QCD, and electroweak theory into a single framework describing fundamental interactions.[23]
See also
Table of contents (185 articles)
Index
Full contents
References
- ↑ R. Oerter (2006). The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern Physics. Penguin Group. p. 2. ISBN 978-0-13-236678-6.
- ↑ R. Mann (2010). An Introduction to Particle Physics and the Standard Model. CRC Press. doi:10.1201/9781420083002-25.
- ↑ 3.0 3.1 C. N. Yang; R. Mills (1954). "Conservation of Isotopic Spin and Isotopic Gauge Invariance". Physical Review 96: 191–195.
- ↑ "The Standard Model". https://www-project.slac.stanford.edu/e158/StandardModel.html.
- ↑ Jens Eisert (2013). "Pauli Principle, Reloaded". Physics.
- ↑ Gregg Jaeger (2021). "Exchange Forces in Particle Physics". Foundations of Physics.
- ↑ 7.0 7.1 P. W. Higgs (1964). "Broken Symmetries and the Masses of Gauge Bosons". Physical Review Letters.
- ↑ F. Englert; R. Brout (1964). "Broken Symmetry and the Mass of Gauge Vector Mesons". Physical Review Letters.
- ↑ G. S. Guralnik; C. R. Hagen; T. W. B. Kibble (1964). "Global Conservation Laws and Massless Particles". Physical Review Letters.
- ↑ S. Weinberg (2004). "The making of the Standard Model". European Physical Journal C.
- ↑ "The Standard Model". CERN. 2023.
- ↑ Abhay Ashtekar (2005). "Gravity and the quantum". New Journal of Physics.
- ↑ "Observation of a New Particle with a Mass of 125 GeV". CERN. 2012.
- ↑ Mary K. Gaillard (1999). "The Standard Model of Particle Physics". Reviews of Modern Physics.
- ↑ Template:Cite news
- ↑ Sean Carroll (2007). Dark Matter, Dark Energy: The Dark Side of the Universe.
- ↑ "The Dirac equation unifies quantum mechanics and relativity". APS. 2024.
- ↑ S. L. Glashow (1961). "Partial symmetries of weak interactions". Nuclear Physics.
- ↑ S. Weinberg (1967). "A Model of Leptons". Physical Review Letters.
- ↑ O. Greenberg (2009). Color Charge Degree of Freedom in Particle Physics.
- ↑ D. Gross; F. Wilczek (1973). "Ultraviolet behavior of non-abelian gauge theories". Physical Review Letters.
- ↑ H. Politzer (1973). "Reliable perturbative results for strong interactions". Physical Review Letters.
- ↑ Gregg Jaeger (2021). "The Elementary Particles of Quantum Fields". Entropy.
Source attribution: Standard Model