5 rep of SU(5) under SU(3)XSU(2)XU(1)

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Discussion Overview

The discussion revolves around the transformation of the 5 representation of SU(5) under the group SU(3)×SU(2)×U(1). Participants are exploring the meaning of the notation used to describe this transformation and seeking resources to better understand the underlying concepts, particularly in the context of Grand Unified Theories (GUTs).

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • One participant asks for clarification on the notation (a,b,c) used to describe how the 5 representation of SU(5) transforms under SU(3)×SU(2)×U(1).
  • Another participant explains that the notation represents an outer product of representations, specifically indicating a triplet of SU(3), a singlet of SU(2), and a weak hypercharge of -1/3.
  • A third participant suggests resources, including Wikipedia and Georgi's "Lie Algebras In Particle Physics," as references for understanding the SU(5) model and its applications in GUTs.
  • One participant mentions familiarity with Clebsch-Gordon decomposition and Young-Tableaux but expresses confusion regarding the specific mathematical processes discussed in Georgi's text, particularly in sections related to SU(3) decomposition.

Areas of Agreement / Disagreement

Participants generally agree on the need for clarification regarding the notation and the mathematical processes involved. However, there is no consensus on the specific understanding of the material in Georgi's book, as one participant expresses uncertainty about the content.

Contextual Notes

Participants reference specific sections of Georgi's book but note that their understanding may vary, indicating potential limitations in grasping the material without further clarification.

Who May Find This Useful

This discussion may be useful for individuals studying particle physics, particularly those interested in group theory applications in GUTs and the mathematical techniques involved in representation theory.

LAHLH
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Hi,

What does is mean to say under SU(3)XSU(2)XU(1) the 5 representation of SU(5) transforms as

5\to(3,1,-1/3) \oplus (1,2,+1/2)

I can't work out what this (a,b,c) notation means exactly; could anyone point me to a link or chapter of a book that could explain what's going on here?

thanks
 
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This decomposes the representation into an outer product of representations of SU(3), SU(2) and SU(1). For example (3,1,-1/3) means 3 ⊗ 1 ⊗ -1/3, the triplet of SU(3), the singlet of SU(2) and weak hypercharge -1/3.
 
Bill_K gave the answer for what the notation means. As for references, you can start with
Wikipedia. The SU(5) model is known as the Georgi–Glashow model and is a simple example of a GUT.

Probably the best intro textbook for this topic is Georgi's Lie Algebras In Particle Physics, where both the SU(5) and SO(10) GUTs are discussed in detail.
 
So I understand how to do a Clebsch-Gordon decomp and the rules of Young-Tableaux, for example I'm happy doing things like 8\otimes 8=\bar{10} \oplus 8 \oplus 8\oplus 1 (well reasonably happy..)...so here we are just decomposing the outer product of two or more representations of a single group into the direct sum of other representations of the group.

I started having a look at p183 of Georgi where he discusses SU(3)\to SU(2)\times U(1), as I think this is a simpler example of the mathematics I need to understand my original post? I'm not sure I follow what is going on in this section (12.3) however, despite feeling I reasonably well understand the previous Young Tableaux stuff. What is he doing to obtain the figure associated with (12.16) and (12.17)?
 

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