The Holographic Entropy Cone for Five Regions

Even though little is known about the quantum entropy cone for $N\ge 4$ subsystems, holographic techniques allow one to get a handle on the subspace of entropy vectors corresponding to states with gravity duals. For static spacetimes and $N$ boundary subsystems, this space is a convex polyhedral cone known as the holographic entropy cone ${\mathcal{C}}_N$ for $N$ regions. While an explicit description of ${\mathcal{C}}_N$ was accomplished for all $N\le 4$ in the initial study, the information given about larger $N$ was only partial already for ${\mathcal{C}}_5$. This letter provides a complete construction of ${\mathcal{C}}_5$ by exhibiting graph models for every extreme ray orbit generating the cone defined by all proven holographic entropy inequalities for $N=5$. The question of whether there exist additional inequalities for $5$ parties is thus settled with a negative answer. The conjecture that ${\mathcal{C}}_5$ coincides with the analogous cone for dynamical spacetimes is supported by demonstrating that the information quantities defining its facets are primitive.