What Does the Second Index in SO(n,p) Represent?

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Discussion Overview

The discussion centers on the meaning of the second index in the notation SO(n,p), particularly in the context of rotation groups and their applications in physics and mathematics. Participants explore the implications of this notation, including its relation to specific groups like the Lorentz group and the conformal group.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that SO(n) represents rotations in n dimensions and seeks clarification on the significance of the second index p.
  • Another participant identifies SO(3,1) and SO(1,3) as the Lorentz group, suggesting that its generalization is straightforward.
  • A different participant mentions that O(n,1) corresponds to the Lorentz group in n spatial dimensions, while O(n,2) represents the conformal group, indicating that there are no special names for cases where p is greater than 2.
  • Another contribution explains that the group SO(m,n) consists of rotations that preserve a symmetric metric with a specific signature, detailing the relationship between SO(m,n) and SO(m+n).

Areas of Agreement / Disagreement

Participants express varying interpretations of the second index in SO(n,p), with some agreeing on its relation to specific groups while others provide different perspectives on its implications. No consensus is reached on a singular interpretation.

Contextual Notes

The discussion does not resolve the underlying assumptions about the definitions of the groups or the implications of the second index, leaving some aspects open to interpretation.

Aziza
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I know that SO(n) means a rotation in n dimensions, but sometimes I see a second index, such as SO(n,p). What does p mean? I cannot find much resources on this.
 
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The special case SO(3,1)(or SO(1,3)) is called Lorentz group. I think its generalization obvious.
 
O(n,1) is the Lorentz group in n space dimensions. O(n,2) is the conformal group in n space dimensions. There are no special names for p>2.
 
The group SO(m,n) is the group of rotations that keep invariant a symmetric metric with signature m + signs and n - signs. The signature is the signs of its eigenvalues. So SO(m,n) is closely related to SO(m+n). Symbolically, for R in SO(m,n) and metric g,
RT.g.R = g
 

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