CLASSICAL AND SEMICLASSICAL PROPERTIES OF EXTREMAL BLACK-HOLES WITH DILATON AND MODULUS FIELDS

We discuss both classical and semiclassical properties of extremal black holes in theories where the dilaton and a modulus field are present. We find that the corresponding 2d geometry is asymptotically anti-de Sitter rather than asymptotically flat as in the purely dilatonic case. This fact has many important consequences, which we analyze at length, both for the classical behaviour and for the thermodynamical properties of the black hole. We also study the Hawking evaporation process in the semiclassical approximation. The calculations strongly indicate the emergence of a stable ground state as the end point of the process. Some comments are made about the relevance of our results for the problem of information loss in black hole physics.