...http://www-dft.ts.infn.it/ ansoldi1
E-mail address: ansoldi@trieste.infn.it 
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...C.Castro2
E-mail address: castro@hubble.cau.edu 
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...http://www-dft.ts.infn.it/ euro3
E-mail address: spallucci@vstst0.ts.infn.it 
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... bi-vector4
We indicate with $\delta^{[ m n ]}$ the antisymmetric symbol while $ \epsilon^ {m n} \equiv \delta^{[ m n ]}/\sqrt g $ is the Levi-Civita tensor. 
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... motion''5
Note that the first term in (19) is independent from the string metric $g_{m n}$. Only the second term contributes to the string energy momentum tensor. 
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... form6
As far as we stick to disk topology world-sheets, we can neglect a transverse harmonic component in the classical momentum. For more general topologies harmonic terms can give non trivial global contributions which must be properly taken into account. 
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...${}$7
By ``confinement'' we mean that there is no leakage of the field current $J_a\equiv \widetilde\eta^\mu\partial_a \widetilde\eta_\mu$ off the world sheet boundary,i.e.

\begin{displaymath} \oint_\gamma dn^a J_a=0 . \end{displaymath} 

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... dynamics8
A boundary term

\begin{displaymath} {1\over 2\sqrt{\mu_0}}\overline P_{\mu\nu}\oint_\gamma dt^... ...\over 2} \oint_\gamma dn^m \eta^\mu \partial_m \eta_\mu \end{displaymath}

vanishes because of the boundary conditions (34),(35). 
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...$Dh_{mn}$9
This functional integration measure has to be factored out by the orbit of the diffeomorphism group, and in the critical dimension by the Weyl group, as well. 
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... disk10
Our result refers to the disk topology. The extension to more complex world sheet topology is straightforward: the single, bulk, partition functional has to be replaced by a sum over definite genus path integrals, i.e. $ Z_{BULK}^A\longrightarrow \sum_g Z_{BULK}^{(g),A}$. This is the starting point for introducing topology changing quantum processes in the framework of string theory. 
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