Grand Unified Theory

A proposed framework in which the strong, weak, and electromagnetic interactions arise from a single interaction at sufficiently high energies. It does not include gravity.

Gauge group: A mathematical group that describes symmetry transformations underlying a gauge theory. Grand unification embeds the Standard Model’s separate gauge symmetries in a larger group.
Standard Model: The quantum field theory describing known elementary particles and the electromagnetic, weak, and strong interactions. A grand unified theory must reproduce the Standard Model at accessible energies.
Georgi–Glashow model: A grand unified theory based on the gauge group SU(5), proposed by Howard Georgi and Sheldon Glashow. It is the simplest prominent model and predicts processes that can test unification.
Electroweak theory: The Standard Model theory unifying electromagnetic and weak interactions. It unifies two forces, whereas grand unification also seeks to include the strong interaction.
Spontaneous symmetry breaking: A state in which a system’s governing laws have a symmetry that its ground state does not display. Breaking a unified symmetry can make the forces appear distinct at lower energies.
Quantum field theory: A framework combining quantum mechanics and special relativity in which particles are excitations of fields. Grand unified models describe interactions through quantum fields and gauge symmetries.
SO(10) grand unified theory: A class of grand unified models based on the gauge group SO(10), which can place each fermion family in one representation. Its particle organization can include a right-handed neutrino within each family.
Theory of everything: A hypothetical framework that would consistently encompass all fundamental interactions, including gravity. Unlike a grand unified theory, it would need to incorporate gravity as well.
Higgs mechanism: A process in quantum field theory through which gauge bosons acquire mass while gauge symmetry remains in the underlying theory. It illustrates how symmetry breaking can produce massive force carriers in unified models.
Electroweak interaction: The unified description of electromagnetic and weak interactions in the Standard Model. Grand unification extends this established unification to include the strong interaction.

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