MASS SUPERSELECTION, CANONICAL GAUGE TRANSFORMATIONS AND ASYMPTOTICALLY FLAT VARIATIONAL-PRINCIPLES

The phase space reduction of Schwarzschild black holes by Thiemann and Kastrup and by Kuchar is re-examined from a different perspective on gauge freedom. This perspective introduces additional gauge transforma tions which correspond to asymptotically nontrivial diffeomorphisms. V arious subtleties concerning variational principles for asymptotically flat systems are addressed which allow us to avoid the usual conclusi on that treating such transformations as gauge implies the vanishing o f corresponding total charges. Instead, superselection rules are found for the (nonvanishing) ADM mass at the asymptotic boundaries. The add ition of phenomenological clocks at each asymptotic boundary is also s tudied and compared with the 'parametrization clocks' of Kuchar.