Unitarity, Analytical Time and Hawking's Temperature
  By analytically continuing the time variable in a black hole background, and requiring unitary evolution, it is found that quantum mechanical states at the horizon develop a thermal factor under suitable identification of the physical time. The thermal factor is found to be determined exactly by the Hawking's temperature. This can be interpreted as the Hawking's radiation and offers an alternative understanding to the process and the information loss puzzle. 
Tze-Dan Chung