Entanglement thermodynamics
  Entanglement entropy is a statistical entropy measuring information loss due to coarse-graining corresponding to a spatial division of a system. In this paper we construct a thermodynamics (entanglement thermodynamics) which includes the entanglement entropy as the entropy variable, for a massless scalar field in Minkowski, Schwarzschild and Reissner-Nordstr{\"o}m spacetimes to understand the statistical origin of black-hole thermodynamics. It is shown that the entanglement thermodynamics in Minkowski spacetime differs significantly from black-hole thermodynamics. On the contrary, the entanglement thermodynamics in Schwarzschild and Reissner-Nordstr{\"o}m spacetimes has close relevance to black-hole thermodynamics. 
Shinji Mukohyama, Masafumi Seriu and Hideo Kodama