Question about Haar measures on lie groups

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Discussion Overview

The discussion revolves around the properties of Haar measures on Lie groups, particularly in the context of changing representations from the fundamental to the adjoint representation. Participants explore whether the Haar measure remains invariant under such transformations.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions if the Haar measure changes when transitioning from the fundamental representation to the adjoint representation, suggesting it should remain invariant due to its properties under left and right translations.
  • Another participant seeks clarification on what specifically is being integrated over the Lie group.
  • A third participant provides an example of a function to be integrated, referencing the Itzykson-Zuber integral involving matrices and the unitary group.
  • Some participants share a link to external resources that may provide additional context or information relevant to the discussion.

Areas of Agreement / Disagreement

The discussion includes some uncertainty regarding the integration process and the implications for the Haar measure, with no clear consensus reached on whether the measure changes or remains invariant.

Contextual Notes

There are unresolved aspects regarding the specific conditions under which the Haar measure is considered invariant, as well as the details of the integration process and the definitions involved.

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I'm not sure if this question belongs to here, but here it goes

Suppose you have to integrate over a lie group in the fundamental representation. If you pass to the adjoint representation of that group, does the Haar measure have to change? I think that it should not change because it is invariant under left and right translations, is it correct?
 
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dextercioby said:
Integrate what?

Some function f: G -> ℝ, where G is the Lie group. For example, the Itzykson-Zuber integral

∫dUexp(-tr(XUYU)), where X, Y are n x n hermitean matrices and U ∈ U(n)
 

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