Tunnelling methods and Hawking's radiation: achievements and prospects

The aim of this work is to review the tunnelling method as an alternative description of the quantum radiation from black holes and cosmological horizons. The method is first formulated and discussed for the case of stationary black holes, and then a foundation is provided in terms of analytic continuation throughout complex spacetime. The two principal implementations of the tunnelling approach, which are the null geodesic method and the Hamilton–Jacobi method, are shown to be equivalent in the stationary case. The Hamilton–Jacobi method is then extended to cover spherically symmetric dynamical black holes, cosmological horizons and naked singularities. Prospects and achievements are discussed in the conclusions.