Book contents
- Frontmatter
- Contents
- Preface to the third edition
- Preface to the first and second editions
- Acknowledgements
- 1 Accelerators, beams and detectors
- 2 Pions and Muons
- 3 Conservation laws
- 4 Strong, weak and electromagnetic interactions
- 5 Strange particles
- 6 Spin and parity of the K-mesons and non-conservation of parity in weak interactions
- 7 Weak interactions: basic ideas
- 8 Invariance under the CP and T operations, properties of K0-mesons
- 9 Strongly-decaying resonances
- 10 SU(3) and the quark model: classification and dynamic probes
- 11 Weak interactions and weak–electromagnetic unification
- 12 New flavours
- 13 Quark and gluon interactions
- 14 Higher symmetries
- 15 Particle physics and cosmology
- 16 Epilogue
- Appendix A Relativistic kinematics and phase space
- Appendix B Clebsch–Gordan coefficients and particle properties
- References
- Index
14 - Higher symmetries
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface to the third edition
- Preface to the first and second editions
- Acknowledgements
- 1 Accelerators, beams and detectors
- 2 Pions and Muons
- 3 Conservation laws
- 4 Strong, weak and electromagnetic interactions
- 5 Strange particles
- 6 Spin and parity of the K-mesons and non-conservation of parity in weak interactions
- 7 Weak interactions: basic ideas
- 8 Invariance under the CP and T operations, properties of K0-mesons
- 9 Strongly-decaying resonances
- 10 SU(3) and the quark model: classification and dynamic probes
- 11 Weak interactions and weak–electromagnetic unification
- 12 New flavours
- 13 Quark and gluon interactions
- 14 Higher symmetries
- 15 Particle physics and cosmology
- 16 Epilogue
- Appendix A Relativistic kinematics and phase space
- Appendix B Clebsch–Gordan coefficients and particle properties
- References
- Index
Summary
Grand unification
We first recall some facts which emerge from the studies and analysis described in the preceding chapters concerning the properties of quarks and leptons. Both quarks and leptons
(i) have spin ½;
(ii) obey the Pauli principle;
(iii) exhibit no internal structure (at the present limit ∼ 10-18 m), i.e. they act as point particles;
(iv) are left-handed in respect of weak processes;
(v) fall into the same kind of doublets for weak processes;
(vi) obey similar gauge theories and interact by exchange of spin 1 bosons.
The only difference we recognise between quarks and leptons is that the quarks carry colour while the leptons do not.
These similarities and the successful unification of the weak and electromagnetic interactions naturally lead to intensive efforts to unify the electro–weak with the strong interactions. Such unification implies the existence of a larger group encompassing
In such a group, the couplings for the different processes would not be independent, so that, for instance, the Weinberg angle θW linking the weak and electromagnetic couplings would be predicted by the theory. All the interactions are then described in terms of a single coupling to which the other couplings can be related once the grand unified group is recognised. Such grand unified theories are frequently referred to by the abbreviation ‘GUTS’.
We recall that the strong coupling decreases as a result of the logarithmic screening term (section 13.3) while the electromagnetic coupling increases due to the screening effect, as a function of momentum transfer.
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- Information
- Elementary Particles , pp. 316 - 331Publisher: Cambridge University PressPrint publication year: 1991