Fabio Iunes Sanches, University of California, Berkeley
The Friedmann, Robertson, Walker (FRW) homogeneous and isotropic model is incredibly successful at describing the large-scale dynamics of our universe. In the FRW metric, the scale factor tells us how distances scale as the universe evolves. Using Einstein’s equations, we see that the energy density determines the dynamical evolution of the scale factor.
Different species contribute to the energy density; however, the varying equations of state imply their dilution is a parametrically different function of the scale factor. In standard cosmological evolution, for example, reheating gives rise to a period of radiation domination, followed by matter, possibly curvature, and finally vacuum energy.
While there are large evidence and examples for the holographic behavior of gravity, a completely satisfactory implementation for cosmology has not yet been achieved. Motivated by entropy bounds, we study surfaces called past and future holographic screens for cosmological models, which have the desired properties for implementing holography in this setting.
Utilizing the holographic entanglement entropy conjecture for general spacetimes we show that the conjectured entanglement entropy considered in  is enough to decode the contribution of different species to the evolution of the scale factor. Furthermore, this suggests a dictionary mapping objects from the holographic screen to usual parameters in cosmology. This is an important step toward holography in cosmological spacetimes.
 “A Holographic Entanglement Entropy Conjecture for General Spacetimes,” Fabio Sanches and Sean J. Weinberg, arXiv:1603:05250
Abstract Author(s): Y. Nomura, N. Salzetta, F. Sanches, S.J. Weinberg