#### marcus

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**Matter-like braids in geometry---video talk by Yidun Wan**

I recently watched this at the Perimeter Institute seminar video website

http://pirsa.org/08010044/

In the various versions of LQG, quantum states of spatial geometry are often represented by networks.

Braids in these networks can behave like particles of matter.

Certain kinds of braids can propagate through the network and it is possible for two different braids to interact---merge and make some other kind of braid.

Yidun Wan has been studying a particular case of this where the network is 4-valent.

One can picture it as a ball and tube "molecule model" where each ball has 4 tubes coming out. However in this model the tubes are quite flexible, so maybe a molecule is not the best picture.

The network is allowed to evolve by certain local moves which affect just one ball, or a few neighbors. The tubes connecting the balls are allowed twist.

It is interesting to see how close the catalog of braid states living in this kind of network comes to the standard menu of particles. If it shows some similarities that would suggest further investigation to see if one can duplicate the standard menu of matter as topological intricacies in spin networks (i.e. in the LQG quantum states of spatial geometry.)

The talk was given on 31 January, just a few days ago. Here is the abstract. To watch the talk, I would suggest clicking on "windows presentation"

**Braid-like Chiral States in Quantum gravity**

Yidun Wan - University of Waterloo

Abstract: There has been a dream that matter and gravity can be unified in a fundamental theory of quantum gravity. One of the main philosophies to realize this dream is that matter may be emergent degrees of freedom of a quantum theory of gravity. We study the propagation and interactions of braid-like chiral states in models of quantum gravity in which the states are (framed) four-valent spin networks embedded in a topological three manifold and the evolution moves are given by the dual Pachner moves. There are results for both the framed and unframed case. We study simple braids made up of two nodes which share three edges, which are possibly braided and twisted. We find three classes of such braids, those which both interact and propagate, those that only propagate, and the majority that do neither.

**These braids may serve as fundamental matter content.**

Date: 31/01/2008 - 2:00 pm

At a couple of points in the presentation Wan is interupted by discussion from others in the seminar which we cannot hear. A couple of these breaks last more than a minute, indicating extended discussion.

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