Simply-connected, complex, simple Lie groups

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Discussion Overview

The discussion revolves around the classification of simply-connected, complex, simple Lie groups, particularly focusing on the groups associated with the Dynkin diagrams Bn and Dn. Participants explore definitions, properties, and seek resources for further information on these groups.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant references John Baez's lecture notes and questions the classification of simply-connected, complex, simple Lie groups for Bn and Dn, noting that SO(n,C) is not simply connected.
  • Another participant clarifies that the simply-connected part refers to the connected component and discusses the properties of various groups, stating that SO(n) is simply connected while O(n) is not.
  • There is a mention that Cn is identified as Sp(2n,C) with its maximal compact subgroup being USp(2n,C).
  • A participant cites a source that lists the groups associated with the Dynkin diagrams, providing specific group identifications for An, Bn, Cn, and Dn.
  • One participant points out that SO(2,C) is connected but not simply connected, referencing a specific source for this claim.
  • Another participant suggests that Baez may have meant "connected" instead of "simply connected" in his classification of Lie groups.

Areas of Agreement / Disagreement

Participants express differing interpretations regarding the definitions of simply-connected and connected groups, and there is no consensus on the classification of the groups associated with Bn and Dn.

Contextual Notes

Some statements rely on specific definitions of connectedness and simply-connectedness, which may not be universally agreed upon. The discussion includes references to external sources for further clarification.

Rasalhague
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I've been looking at John Baez's lecture notes "Lie Theory Through Examples". In the first chapter, he says Dynkin diagrams classify various types of object, including "simply-connected, complex, simple Lie groups." He discusses the An case in detail. But what are the simply-connected, complex, simple Lie groups associated with Bn and Dn? SO(n,C) is not simply connected. Spin(n) and PSL(n,C) are compact and, says Baez, "a complex simple Lie group is never compact."

Is there a good source online which lists all the simply-connected, complex, simple Lie groups and their maximal compact subgroups as Baez does for An?

I believe Cn is Sp(2n,C) with maximal compact subgroup USp(2n,C), the latter commonly written Sp(n).
 
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If one refers to the simply-connected part, then the connected component of ##1## is meant. And I think ##O(n)## isn't simply connected, ##SO(n)## is. If ##n## denotes the number of simple roots, or knots in the Dynkin diagram, then

##A_n \triangleq SL(n+1)##
##B_n \triangleq O(2n+1) , SO(2n+1)##
##C_n \triangleq SP(2n)##
##D_n \triangleq O(2n) , SO(2n)##

As it's from SUNY I suppose it's o.k. to quote here without violating any copyrights:
https://www.math.stonybrook.edu/~kirillov/mat552/liegroups.pdf
 
I guess he must have meant "connected" rather than "simply connected" when he writes that Dynkin diagrams classify "a bunch of things" including: "simply connected complex simple Lie group" and "compact simply connected simple Lie groups".
 

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