Embedding variables in the canonical theory of gravitating shells

A thin shell of light-like dust with its own gravitational field is studied in the special case of spherical symmetry. The action functional for this system due to Louko, Whiting, and Friedman is reduced to Kuchar: form: the new variables are embeddings, their conjugate momenta, and Dirac observable s. The concepts of background manifold and covariant gauge fixing, that und erlie these variables, are reformulated in a way that implies the uniquenes s and gauge invariance of the background manifold. The reduced dynamics des cribes motion on this background manifold. (C) 2001 Elsevier Science B.V. A ll rights reserved.