Islands in Generalized Dilaton Theories

In this work we systematically study the island formula in the general asymptotically flat eternal black holes in generalized dilaton gravity theories or in higher dimensional spherical black holes. Under some reasonable and mild assumptions we prove that the island always appears barely outside of the horizon in the late time of Hawking radiation so that the information paradox is resolved. In particular, we find proper island in Liouville black hole which solves the puzzle of arXiv:2105.03271.