# Help on QFT

1. Aug 14, 2004

### marlon

Hi, can anyone give me a clear definition of the following two things

1) Wilson loop
2) Spin network (invented by Penrose, right???)

What do these quantities fysically mean???

PS : can anyone explain me what the term LOOP means in Loop quantum gravity. To what does it refer ?

regards
marlon

2. Aug 15, 2004

### humanino

Hey Marlon !

Very intersting issues...that I don't want to pretend I undestand though But I want to advise you a very good paper on quantum gravity by Carlo Rovelli. This is an entire book, whose draft version is available at :
http://www.cpt.univ-mrs.fr/~rovelli/rovelli.html

Anything I could say would be more accurate in this paper. Enjoy ! :tongue2:

3. Aug 15, 2004

### marlon

grazie, humanino

how is life out there in Paris???

4. Aug 15, 2004

### humanino

je vous en prie Marlon, c'est mon plaisir

Another (shorter) paper
http://www.wordiq.com/definition/Loop_quantum_gravity
Should this move to another forum (LQG !!)?

Last edited by a moderator: Apr 21, 2017
5. Aug 15, 2004

### humanino

I took one week out of my thesis. Back to Switzerland Jura ! This is also how I come to have time to read useless things such as LQG :tongue2:

Could someone elaborate on Penrose and spin network ?

6. Aug 15, 2004

### humanino

I give here the definition of the Wilson loop given by Zinn-Justin in his "QFT & Critical phenomena"

section 33.3 "Wilson's loop and confinement" (p735)
$$W(C)=\left\langle e^{-ie \oint_{C} A_\mu(s) ds_\mu } \right\rangle$$
with C a closed loop in space-time. This is a functional integral, and represents the parrallel transporter along the closed loop.

As for spin network :
http://www.wordiq.com/definition/Spin_network

Last edited by a moderator: Apr 21, 2017