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

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SUMMARY

Pin Groups serve as the double cover of the Orthogonal Group, while Spin Groups act as the double cover of the Special Orthogonal Group. Both Pin and Spin Groups are classified as groups, but only one of these double covers contains the identity element, confirming that both cannot be groups simultaneously. The distinction lies in the determinant values, where the subset with determinant equal to -1 does not form a group, while the subset with determinant equal to 1 does.

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  • Understanding of group theory and its definitions
  • Familiarity with Orthogonal Groups and Special Orthogonal Groups
  • Knowledge of double covers in mathematical contexts
  • Basic comprehension of determinants in linear algebra
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  • Investigate the role of determinants in classifying groups
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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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$$
\underbrace{\{\ldots \det =\pm 1\}}_{\text{Group}}=\underbrace{\{\ldots \det =-1\}}_{\text{ no Group}}\cup \underbrace{\{\ldots \det =1\}}_{\text{Group}}
$$
 
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Got it; thanks!
 
redtree said:
Got it; thanks!
Just to be clear, both Pin and Spin are groups.
 

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