Towards self dual Loop Quantum Gravity Jibril Ben Achour

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Discussion Overview

The discussion revolves around a new research direction in Loop Quantum Gravity (LQG) as presented in Jibril Ben Achour's PhD thesis, which explores the concept of self-dual LQG. Participants examine the implications of using self-dual variables, the role of the Immirzi parameter, and the potential advantages of this approach in understanding quantum gravity and black hole entropy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants highlight the advantages of the original Ashtekar self-dual variables, suggesting that they may provide new insights into LQG.
  • There is a question regarding the benefits of making LQG self-dual, with some participants seeking clarification on this aspect.
  • One participant notes that the Immirzi parameter may be treated as a regulator that allows for a Wick rotation of the kinematical quantum theory, potentially leading to a self-dual quantum theory.
  • Another participant recalls that earlier thoughts suggested the Immirzi parameter should match the Hawking formula, but recent discussions indicate that an imaginary Immirzi parameter may be more relevant in the context of LQG black holes.
  • There is mention of Steve Carlip's work, which also addresses the implications of setting the Immirzi parameter to an imaginary value for better semiclassical black hole entropy calculations.
  • Participants reference the original Kodama wave function, which is associated with the condition of the Immirzi parameter being equal to i.

Areas of Agreement / Disagreement

Participants express varying views on the implications and interpretations of the self-dual LQG framework and the role of the Immirzi parameter. There is no consensus on the benefits or interpretations of these concepts, indicating ongoing debate and exploration.

Contextual Notes

Participants discuss the potential limitations and assumptions related to the Immirzi parameter and its implications for quantum gravity, but these aspects remain unresolved within the discussion.

kodama
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interesting new paper on possible new research direction for LQG

http://arxiv.org/abs/1511.07332
Towards self dual Loop Quantum Gravity
Jibril Ben Achour
(Submitted on 23 Nov 2015)
In this PhD thesis, we introduced a new strategy to investigate the kinematical and physical predictions of self dual Loop Quantum Gravity (LQG) and by-passed the old problem of implementing quantum mechanically the so called reality conditions inherent to the self dual Ashtekar's phase space.
We first review the loop quantization of the spherically isolated horizon and the computation of its micro-canonical entropy. Then we present the so called gas of punctures model for the quantum horizon, discussing its results in the canonical and grand-canonical ensembles and its limits.
The fourth chapter is devoted to studying to what extend the loop quantization based on the self dual variables could cure those problems. We introduce a new strategy, based on an analytic continuation of the degeneracy from γ∈R to γ=±i. We review in details the construction of the procedure, and present the results. At the leading term, we recover exactly the Bekenstein-Hawking area law.
The fifth chapter is devoted to understanding more precisely the interplay between the status of the Immirzi parameter. In order to do this, we introduce from a new toy model describing 2+1 gravity which depends explicitly on the Immirzi parameter.
Finally, the sixth chapter is devoted to applying our procedure to the simplest Loop Quantum Cosmology model. By first constructing the LQC dynamics for any arbitrary spin j and then implementing our analytic continuation, we show that our procedure preserves the key features of the LQC models, i.e. we obtain a bouncing universe which admits the right semi classical limit after the bounce.
PhD Thesis - 254 pages

worth remembering since the paper is about self-dual LQG
 
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good idea there marcus. when LQG when y= i it is self-dual. what are the benefits of making LQG self-dual
 
It seems to be related to the line of work which tries to make Immizi imaginary. Originally the thinking was the Immirzi should be set to match the Hawking formula? But I think some more recent thinking on LQG black holes has imaginary Immirzi.

Eg. slide 17 of http://www.ihes.fr/~vanhove/Slides/NOUI-IHES-novembre2013.pdf

From Ben Achour's thesis in the OP (p79):
"Going further in our interpretation, the Immirzi parameter could be regarded as a kind of regulator, allowing to Wick rotate the kinematical quantum theory. At the end of the quantization procedure, should be sent to the purely imaginary value, in order to recover to self dual quantum theory. This is the point of view adopted in this manuscript."
 
Last edited:
atyy said:
It seems to be related to the line of work which tries to make Immizi imaginary. Originally the thinking was the Immirzi should be set to match the Hawking formula? But I think some more recent thinking on LQG black holes has imaginary Immirzi.

Eg. slide 17 of http://www.ihes.fr/~vanhove/Slides/NOUI-IHES-novembre2013.pdf

From Ben Achour's thesis in the OP (p79):
"Going further in our interpretation, the Immirzi parameter could be regarded as a kind of regulator, allowing to Wick rotate the kinematical quantum theory. At the end of the quantization procedure, should be sent to the purely imaginary value, in order to recover to self dual quantum theory. This is the point of view adopted in this manuscript."

i recall Steve Carlip had a paper on that as well. his thesis is y = i results in better semiclassical black hole entropy calculation.

worth noting that the original kodama wave function y = i
 
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