Pseudo Real Group if anomaly free

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Discussion Overview

The discussion revolves around the relationship between pseudo-real representations of groups and their implications for anomaly cancellation in the context of particle physics, specifically referencing concepts from unification and supersymmetry as presented in the Mohapatra textbook.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks to demonstrate that if a representation of a group is pseudo-real, it is automatically anomaly free, noting the lack of detailed guidance in the relevant textbook chapter.
  • Another participant suggests posting the question on a different forum frequented by experts in string theory, indicating that they may have more relevant insights on anomaly cancellation.
  • A participant provides a technical explanation, mentioning that left-handed fermion fields in pseudo-real representations relate to their complex conjugate representations, which is crucial for understanding anomaly calculations.
  • This participant elaborates on the anomaly calculation process, emphasizing the separation of symmetric and antisymmetric parts in the three-point function and the algebra involved in demonstrating anomaly freedom.
  • A later reply expresses a need for further clarification on anomaly calculations, referencing the use of Young tableaux and seeking specific equations related to the three-point function from established quantum field theory texts.

Areas of Agreement / Disagreement

Participants present various viewpoints and technical details, but there is no consensus on the best approach to demonstrate the anomaly freedom of pseudo-real representations. The discussion remains unresolved with multiple perspectives on the topic.

Contextual Notes

Participants mention the need for careful algebraic manipulation and the potential for gauge anomalies in standard model groups, indicating that some assumptions and definitions may need further clarification.

robousy
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I am working a problem from the Mohapatra textbook unification and supersymmetry and the question is to show that if any rep of a grp is pseudo real then it is automatically anomaly free.


There is not much in the chapter (2) on how to go about this.

All I know is that for a pseudo real group G = G* (the conjugate is the same as the original group). The group is not real though.

I've been searching the web and books for a couple of hours now to no avail so thought I'd leave the question here.
 
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May I suggest you post this question on the sci.physics.strings board, which you can access through the Strings Branes and LQG subforum. That board is visited by expert string theorists who are likely to have an answer for your question; they are very interested in anomaly cancelation. But they are not likely to visit this Particle Physics subforum.
 
ok, thanks!
 
Mmm, this is a bit of a technical question, you'll want to double check me (say with Weinberg vol 2).

But you basically listed the reason *why*, namely when the left handed fermion fields furnish reps that are equivalent to the complex conjugate rep. Eg the representation of the gauge algebra (take its complex conjugate) is related by a similarity transformation to itself

To see this, remember when you calculate the anomaly from the three point function, you can separate it into symmetric and antisymmetric parts by group index. The anomaly is wholely contained in the symmetric part of this, so you have to do a little bit of algebra (subbing in the similarity condition of the representation into the symmetric part) and you will come out with the required reality or pseudo reality to be anomaly free.

Note that some standard model groups will contain this gauge anomaly, so there you will have to look for cancellations to occur, or else you have an inconsistent theory. Its one of the miracles of SU(3)*SU(2)*U(1) that the required cancellations *do* occur (a deeper reason maybe is that this group is an rep of SO(10) which is by the above anomaly free)
 
Last edited:
Haelfix said:
To see this, remember when you calculate the anomaly from the three point function, you can separate it into symmetric and antisymmetric parts by group index. The anomaly is wholely contained in the symmetric part of this, so you have to do a little bit of algebra (subbing in the similarity condition of the representation into the symmetric part) and you will come out with the required reality or pseudo reality to be anomaly free.


Hey Haelfix. Thanks for your response. I'm still getting used to calculating the anomaly. I've done is so far using young tableux and I've also seen an equation in Mohapatras book that is related to the trace of generators.
Could you possibly give me a reference to the equation you are tallking about - ie regarding the 3 pt function. I have most QFT books - perhaps Weinberg vol 2?

Thanks again.

:smile:
 

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