Evaporation and fate of dilatonic black holes

We study both spherically symmetric and rotating black holes with dilaton coupling and discuss the evaporation of these black holes via Hawkings quantum radiation and their fates. We find that the dilaton coupling constant drastically affects the emission rates, and therefore the fates of the black holes. When the charge is conserved, the emission rate from the nonrotating hole is drastically changed beyond =1 (a superstring theory) and diverges in the extreme limit. In the rotating cases we analyze the slowly rotating black hole solution with arbitrary as well as three exact solutions: the Kerr-Newman (=0), Kaluza-Klein (= 3), and Sen black hole (=1 and with axion field). Beyond the same critical value of 1, the emission rate becomes very large near the maximally charged limit, while for <1 it remains finite. The black hole with >1 may evolve into a naked singularity due to its large emission rate. We also consider the effects of a discharge process by investigating superradiance for the nonrotating dilatonic black hole.