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QUANTUM MECHANICS AND NON-ABELIAN THETA FUNCTIONS ...

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26RĂZVAN GELCA <strong>AND</strong> ALEJ<strong>AND</strong>RO URIBEVkVlVmVpVqVnFigure 5then color it by the representation V n of U (sl(2, C)). Add two basis elementse p and e q , viewed as colorings by irreducible representation of thecores of the interior, respectively exterior handlebodies (see Figure 6).VbiV VjV nVkVcaVFigure 6Forget the surface to obtain an oriented tangled ribbon graph in S 3 whoseedges are decorated by irreducible representations of U (sl(2, C) (Figure 7).By projecting this graph on a plane while keeping track of the crossings(which is over, which is under), one can think of the edges as the trajectoriesof 1-dimensional quantum particles with the y-axis as the time direction.The diagram then yields a unitary evolution operator from the Hilbert spaceof a system without particles to the Hilbert space of a system without particles,hence a linear map from C to C. This linear map is the multiplicationby a complex number. The Reshetikhin-Turaev theory [20] gives a way ofcomputing this number, which is independent of the particular projectionand is called the Reshetikhin-Turaev invariant of the framed graph.tbVnVVaViV jVkV cxFigure 7In short, the Reshetikhin-Turaev invariant is computed as follows. Theribbon graph should be mapped by an isotopy to one which, when projected,

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