De Sitter entropy: on-shell versus off-shell

Abstract: Attributing thermodynamic properties to the Bunch-Davies state in static patch of de Sitter space and setting the corresponding equations of state, we demonstrate that, for pure gravity, the bulk entropy computed on-shell as a volume integral in de Sitter space coincides with the Wald entropy (area law) in any spacetime dimension and for any theory of f(R) gravity. We extend this result to the renormalized entanglement entropy of a non-minimally coupled scalar field. From the on-shell perspective, entropy emerges as a bulk contribution, whereas from the off-shell viewpoint, it manifests as a boundary (horizon) contribution. As a result, in de Sitter space, generalized entropy can be understood in two distinct ways: either as a bulk or as a boundary contribution.