A Kaehler Structure on the Space of String World-Sheets

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Let (M,g) be an oriented Lorentzian 4-manifold, and consider the space S of oriented, unparameterized time-like 2-surfaces in M (string world-sheets) with fixed boundary conditions. Then the infinite-dimensional manifold S carries a natural complex structure and a compatible (positive-definite) Kaehler metric h on S determined by the Lorentz metric g. Similar results are proved for other dimensions and signatures, thus generalizing results of Brylinski regarding knots in 3-manifolds. Generalizing the framework of Lempert, we also investigate the precise sense in which S is an infinite-dimensional complex manifold.