Retrieving the loops on spinfoams

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Discussion Overview

The discussion revolves around the retrieval of a specific paper related to spinfoams and the graphical representation of closed loops associated with them. Participants explore concepts related to loop quantum gravity (LQG), including orientations of links and the implications for loop states in spin networks.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks a paper on a graphical method to visualize closed loops in spinfoams, suggesting it might involve lines on edges.
  • Another participant proposes a specific paper as a potential match but acknowledges it may be more complex than what was originally sought.
  • A different participant recalls the paper being simpler and possibly authored by Smolin or Rovelli.
  • Discussion includes a description of how loops can be drawn based on following edges in a finite connected spinfoam, leading to the concept of parallel loop lines.
  • One participant shares a paper on spin networks and the bracket polynomial, noting its relevance to the epsilon tensor in LQG intertwiners.
  • Another participant mentions a book by Louis H. Kauffman that provides a deeper introduction to the mathematics involved, expressing uncertainty about the physics aspects.
  • A participant raises a concern about managing orientations of loops in recoupling theory, questioning how loops with orientations can interact with nodes that have only ingoing links.
  • Some participants reflect on their experiences with related literature, including Rovelli's work and its accessibility.
  • One participant specifically references Rovelli's book and its section on spin networks, highlighting the challenge of understanding loop orientations.

Areas of Agreement / Disagreement

Participants express various viewpoints and uncertainties regarding the specific paper sought, the nature of loops in spinfoams, and the implications of orientations in loop quantum gravity. No consensus is reached on these topics.

Contextual Notes

Participants note limitations in their understanding of LQG and the complexities involved in the orientation of loops and links, indicating that further clarification and exploration are needed.

Heidi
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I am looking for a paper i read several yeais ago.
is was on a graphical way to see all the closed loops associated to an oriented spinfoam. there was a set of lines on each edge.
do you see what i mean?
thanks
 
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It was more simple that this paper. more like a trick than a theory...
with an author like smolin or rovelli (maybe).
 
You really should try to find the paper and post the link. Others might be interested.
 
what i remember is that in finite connected spinfoam if you are on an edge and follow a random outgoing edge when you meet a node you will follow a closed path ending on the startind edge. this is a loop that you can draw near the edges. other choices would give over loopq and over drawings.
so you get for each edge parrallel different loop lines.
Draw the Mercedes cirle with 3 segments , choose orientations for the edges (at less one ingoing and one outgoing one each nodes) and see the loops ...
 
I found this interesting paper
SPIN NETWORKS AND THE BRACKET POLYNOMIAL
https://homepages.math.uic.edu/~kauffman/spinnet.pdf
it gives the identities of the binor calcus based on the properties of the epsilon tensor. this epsilon tensor appears in the LQG intertwiners.
 
Louis H. Kauffman wrote a book ”Knots and Physics” which might be of interest as it provides a more in depth introduction to the mathematic. I go through phases on things like this. Never quite clear on how much of it is really physics.
 
Hi Paul,
there is something that bothers me.
Links in LQG have orientations so a node can have only ingoing links.
But consider the loops in the recoupling theory. we have strands associated with links
ie if a link has a j spin we find 2j lines in the strand. if they correspond to loops they should
have an orientation. How to manage these orientations? what if such a loop goes thru the node with only ingoing links?
 
Sorry, I haven’t looked at LQG closely enough to even guess. Several years ago I did attempt a reading of a paper that approached QED from a loop approach similar to LQG. My hope was to gain insight by looking at how a theory I partially understand is handled.

BTW I took another swing at “Knots and Physics”. It’s quite readable.
 
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Haven’t looked at it. I’m probably ripe for another LQG attempt. Thanks for the link.
 
  • #12
When i opened this thread , i had in mind what Rovelli wrote in in the 6.3.2 paragraph.(details on the spin networks)
see how from a simple spin network he obtains the corresponding loop states
the remainig problem for me is the orientation of the loops.
 

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