BLACK-HOLE EVAPORATION WITHOUT INFORMATION LOSS

An approach to black hole quantization is proposed wherein it is assum ed that quantum coherence is preserved. After giving our motivations f or such a quantization procedure we formulate the background field app roximation, in which particles are divided into 'hard' particles and ' soft' particles. The background spacetime metric depends both on the i n-states and on the out-states. A consequence of our approach is that four-geometries describing gravitational collapse will show the same t opological structure as flat Minkowski space. We present some model ca lculations and extensive discussions. In particular, we show, in the c ontext of a toy model, that the S-matrix describing soft particles in the hard particle background of a collapsing star is unitary; neverthe less, part of the spectrum of particles is shown to be approximately t hermal. We also conclude that there is an interesting topological (and signature) constraint on manifolds underlying conventional functional integrals.