Home > Grand unification theory

1 Proposed theories

Several such theories have been proposed, but none is currently universally accepted. An even more ambitious theory that includes all fundamental forces, including gravitation, is termed a theory of everything. Some common mainstream GUT models are:

• Georgi-Glashow model -- SU(5)
• SO(10)
• Flipped SU(5) -- SU(5)× U(1)
• Pati-Salam model -- SU(4)× SU(2)× SU(2)
• Trinification -- SU(3)× SU(3)× SU(3)
• E₆Lie groups In mathematics, E is the name of a Lie group and also its Lie algebra. It is one of the five exceptional simple Lie groups as well as one of the simply laced groups. E has rank 6 and dimension 78. Its fundamental representation is 27-dimensiona
• Technicolor modelsTechnicolor models are GUT theories which do not have a scalar Higgs field. Instead, they have a larger number of fermion fields than the Standard Model and involve a larger gauge group. This larger gauge group is spontaneously broken down to the Standard

Note: These models refer to Lie algebras not to Lie groups. The Lie group could be [SU(4)×SU(2)×SU(2)]/Z₂, just to take a random example.

GUT models generically predict the existence of topological defects such as monopoles, cosmic strings, domain walls, and others. None have been observed and their absence is known as the monopole problem in cosmology.

2 Current status

GUT theories are based on the idea of a "desert" with no new physics of several orders of magnitude in the renormalization group. However, it is a bit suspicious to run the renormalization group backwards because we don't know what new physics lie there and the property of universality suggests we can't tell easily either.

3 See also

• Grand Unification Energy