Entanglement of self interacting scalar fields in an expanding spacetime
  We evaluate self-interaction effects on the quantum correlations of field modes of opposite momenta for scalar $\lambda \phi^4$ theory in a two-dimensional asymptotically flat Robertson-Walker spacetime. Such correlations are encoded both in the von-Neumann entropy defined through the reduced density matrix in one of the modes and in the covariance expressed in terms of the expectation value of the number operators for each mode in the evolved state. The entanglement between field modes carries information about the underlying spacetime evolution. 
Helder Alexander, Gustavo de Souza, Paul Mansfield, I. G. da Paz,   Marcos Sampaio
hep-th