Principles for a Distinguished Global Vacuum: Entropy and the Vacuum State in Causal Set Theory

Using the framework of real scalar field theory on causal sets, the intimate relation of the Sorkin-Johnston vacuum to entropic purity is elucidated. It is shown that taking a set of sensible principles, and the most natural assumption on the space of fields, leaves the Sorkin-Johnston state as the only candidate for the global vacuum of a quasifree theory.