EVAPORATION AND FATE OF DILATONIC BLACK-HOLES

We study both spherically symmetric and rotating black holes with dila ton coupling and discuss the evaporation of these black holes via Hawk ing's quantum radiation and their fates. We find that the dilaton coup ling constant alpha drastically affects the emission rates, and theref ore the fates of the black holes. When the charge is conserved, the em ission rate from the nonrotating hole is drastically changed beyond al pha = 1 (a superstring theory) and diverges in the extreme limit. In t he rotating cases we analyze the slowly rotating black hole solution w ith arbitrary alpha as well as three exact solutions: the Kerr-Newman (alpha = 0), Kaluza-Klein (alpha = root 3), and Sen black hole (alpha = 1 and with axion field). Beyond the same critical value of alpha sim ilar to 1, the emission rate becomes very large near the maximally cha rged limit, while for alpha < 1 it remains finite. The black hole with alpha > 1 may evolve into a naked singularity due to its large emissi on rate. We also consider the effects of a discharge process by invest igating superadiance for the nonrotating dilatonic black hole.