| |
|
Since the Georgi-Glashow model combines leptons and quarks into single irreducible representations there exist interactions which do not conserve baryon number. This yields a mechanism for proton decay, and the rate of proton decay can be predicted from the dynamics of the model. However, proton decay has not yet been observed experimentally, and the resulting lower limit on the lifetime of the proton contradicts the predictions of this model. However, the elegance of the model has led particle physicists to use it as the foundation for more complex models which yield longer proton lifetimes.
SU(5) breaking occurs when a scalar field, analogous to the Higgs field, and transforming in the adjoint of SU(5) acquires a vacuum expectation value proportional to the hypercharge generator
Breaking SU(5)
When this occurs SU(5) is spontaneously broken to the subgroup of SU(5) commuting with the group generated by Y. This unbroken subgroup is just the standard model group: [SU(3)×SU(2)×U(1)]/Z6.
Under the unbroken subgroup the adjoint 24 transforms as
The standard model quarks and leptons fit neatly into representations of SU(5). Specifically, the left-handed fermions combine into 3 generations of . Under the unbroken subgroup these transform as
Since the homotopy group