Pin & Spin Groups: Double Covers of Orthogonal & SO Groups

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Discussion Overview

The discussion centers on the properties of Pin and Spin groups as double covers of the Orthogonal and Special Orthogonal groups, respectively. Participants explore whether both sets qualify as groups, particularly in relation to the identity element and determinants.

Discussion Character

  • Debate/contested, Technical explanation

Main Points Raised

  • One participant asserts that Pin Groups are the double cover of the Orthogonal Group and Spin Groups are the double cover of the Special Orthogonal Group, questioning the group status of both due to the identity element.
  • Another participant presents a mathematical representation suggesting that while one subset with determinant = 1 forms a group, the subset with determinant = -1 does not, implying a division in group status.
  • Some participants express agreement with the clarification that both Pin and Spin are indeed groups.

Areas of Agreement / Disagreement

There is some disagreement regarding the group status of the Pin and Spin groups, particularly concerning the identity element and the determinants. While some participants agree that both are groups, the initial question raises uncertainty about this conclusion.

Contextual Notes

The discussion involves assumptions about the definitions of groups and the role of the identity element, which remain unresolved. The mathematical steps regarding determinants are not fully explored.

redtree
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TL;DR
Do both sets of the double cover contain an identity element?
Pin Groups are the double cover of the Orthogonal Group and Spin Groups are the double cover of the Special Orthogonal Group. Both sets of the double cover are considered to be groups, but it seems that only one of the sets of the double cover actually contains the identity element, which means that both are not groups. Am I missing something?
 
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$$
\underbrace{\{\ldots \det =\pm 1\}}_{\text{Group}}=\underbrace{\{\ldots \det =-1\}}_{\text{ no Group}}\cup \underbrace{\{\ldots \det =1\}}_{\text{Group}}
$$
 
  • Like
Likes   Reactions: redtree
Got it; thanks!
 
redtree said:
Got it; thanks!
Just to be clear, both Pin and Spin are groups.
 

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