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**Noncommutative Geometries from "first principles"**

Hi everyone,

to give a motivation for studying specific models of noncommutative geometry, I would like to start this thread as a collecting tank of models of noncommutative geometry that

*are obtained as a limit of some kind from 'first principles', i.e. not an ad-hoc modification of the commutator [x_i,x_j]*. It would be nice, if we could collect cases by briefly stating what theory in which limit they are obtained from, provide the specific form of the coordinate commutator, and cite a reference (if possible, respectively). So, as a start:

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From 2+1-dim. Spinfoams, by integrating out gravitational DOF, to arrive at the flat-space effective field theory:

[tex] [X_i, X_j]=i\hbar \kappa \epsilon_{ijk} X_k, \quad \kappa = 4\pi G [/tex]

Reference: http://arxiv.org/abs/0705.2222

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As some knowledgeable people are around here, I hope some members share interest in this and contribute . For example I heard in string theory world-sheet coordinates do not commute, but I don't know much about it, i.e. which precise form in which case.