Hawking-Unruh effect and the entanglement of two-mode squeezed states in   Riemannian spacetime
  We consider the system of free scalar field, which is assumed to be a two-mode squeezed state from an inertial point of view. This setting allows the use of entanglement measure for continuous variables, which can be applied to discuss free and bound entanglement from the point of view from non-inertial observer. 
D. Ahn and M. S. Kim