The Standard Model of Particle Physics
The Standard Model of particle physics is a comprehensive theory that describes three of the four known fundamental forces in the universe: the electromagnetic force, the weak nuclear force, and the strong nuclear force. It also classifies all known elementary particles. The only fundamental force not described by the Standard Model is gravity, which is currently described by general relativity.
Elementary Particles
In the framework of the Standard Model, an elementary particle is a subatomic particle that is not composed of other particles. These particles are the fundamental constituents of matter and energy. The Standard Model categorizes these particles into two groups: fermions and bosons.
Fermions
Fermions are particles that follow Fermi-Dirac statistics and make up all matter. They obey the Pauli exclusion principle, which states that no two fermions can occupy the same quantum state simultaneously. Fermions are further divided into quarks and leptons.
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Quarks: These are fundamental constituents of composite particles called hadrons, the most stable of which are protons and neutrons. Quarks come in six "flavours": up, down, charm, strange, top, and bottom. They are held together by the strong force, mediated by gluons.
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Leptons: These are elementary particles that do not experience the strong force. The best-known lepton is the electron, which is essential to the structure of atoms. Other leptons include muons, taus, and three types of neutrinos.
Bosons
Bosons are force-carrying particles that follow Bose-Einstein statistics. They act as carriers of the fundamental forces of nature.
- Photons are responsible for mediating the electromagnetic force.
- W and Z bosons mediate the weak nuclear force, which is responsible for radioactive decay processes.
- Gluons are the exchange particles for the strong nuclear force, binding quarks together in protons and neutrons.
- The Higgs boson provides other particles with mass through the Higgs mechanism.
Mathematical Formulation
The mathematical foundation of the Standard Model is based on the principles of quantum field theory and gauge symmetries. It incorporates the internal symmetries of the unitary product group SU(3) × SU(2) × U(1), which correspond to the strong, weak, and electromagnetic forces, respectively.
Beyond the Standard Model
While the Standard Model is incredibly successful in explaining a vast array of physical phenomena, it is incomplete. It does not incorporate gravity, nor does it account for the dark matter and dark energy that appear to make up most of the universe. Physics beyond the Standard Model explores theories like supersymmetry and string theory to address these gaps.