Anomaly Cancellation for GUTS: Beginner's Questions

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SUMMARY

Anomaly cancellation is a critical requirement in Grand Unified Theories (GUTs) to maintain local gauge invariance. The discussion highlights that while global symmetries can have anomalies, local gauge invariance must be preserved to avoid theoretical inconsistencies. Consistency equations are employed to ensure that anomalous terms are counterbalanced by other terms. Certain Lie groups, such as SO(10), automatically provide anomaly-free representations, whereas GUTs with additional U(1) factors require careful consideration to avoid anomalies.

PREREQUISITES
  • Understanding of local gauge invariance in quantum field theory
  • Familiarity with Grand Unified Theories (GUTs)
  • Knowledge of Lie groups and their representations
  • Basic concepts of anomalies in quantum field theories
NEXT STEPS
  • Research the role of consistency equations in anomaly cancellation
  • Study the properties of SO(10) and other Lie groups in GUTs
  • Explore the implications of the axial anomaly in Quantum Chromodynamics (QCD)
  • Investigate the effects of additional U(1) factors in GUT models
USEFUL FOR

The discussion is beneficial for theoretical physicists, graduate students in particle physics, and researchers focusing on Grand Unified Theories and gauge invariance issues.

robousy
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Beginners question :

In GUTS what is the relevance of anomaly cancellation.

Is it in some sense an axiom - like we say we must have local invariance - or is it in just some mathematical requirement?

Thanks in advance.
 
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We don't care too much about global symmetries being anomalous, for instance the axial anomaly of QCD.

Otoh if we have anomalies that break local gauge invariance, we have a serious problem, the theory is necessarily inconsistent (both theoretically and by experiment, gauge invariance is key). So people devised consistency equations to ensure that anomalous terms were matched with other (often adhoc) terms that precisely cancel.

Now as far as GUTs go, some lie groups furnish anomaly free irreps automatically (eg SO(10)), its usually the GUTs with extra U(1) factors lying around that you ahve to be careful with.
 
So its not really an axiom - more a requirement.
 

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