Alladi Ramakrishnan Hall

Extremal surfaces, entanglement in ghost systems and de Sitter entropy

K. Narayan

CMI

Certain conjectures generalizing gauge/gravity duality (dS/CFT) for de Sitter space involve nonunitary Euclidean CFT duals akin to ghost-CFTs for dS4 where the central charge is negative. We study codim-2 extremal surfaces in de Sitter space, Poincare slicing, as possible probes modelling holographic entanglement entropy, generalizing Ryu-Takayanagi in AdS/CFT. We then explore negative entanglement in toy ghost-CFTs and ensembles of "ghost-spins" (2-state spin variables with indefinite norm). Finally in the static coordinatization of de Sitter, we find real timelike codim-2 extremal surfaces stretching between the future and past boundaries. In a certain limit, these pass through the bifurcation region and have divergent area with coefficient de Sitter entropy in 4-dimensions. This leads to some speculations on dS4 as dual to two copies of ghost-CFTs in particular entangled states.