Compactification of moduli spaces of extremals of 2-dimensional conformally invariant variational problems

An extension ℒ′O(M) of the space Ω2(M)′ of De Rham currents on a manifold M better adapted to the study of conformally invariant variational problems, is introduced. This extension is the dual of the space of conformally invariant first-order Lagrangian densities for maps from ℂ to M. A map from the moduli space of maps from a Riemann surface (Σ, j) to M to ℒO(M)′ , is defined, and its restriction to the moduli of embeddings is proved to be injective. A general result of compactness on ℒO(M)′ is stated and used to obtain compactifications of subsets of the moduli space. In the particular case of J-holomorphic curves such a compactification is compared with Gromov's compactification.