Abstract
Gravitational thermodynamics and gravitoscalar thermodynamics with S2 × ℝ boundary geometry are investigated through the partition function, assuming that all Euclidean saddle point geometries contribute to the path integral and dominant ones are in the B3 × S1 or S2 × Disc topology sector. In the first part, I concentrate on the purely gravitational case with or without a cosmological constant and show there exists a new type of saddle point geometry, which I call the “bag of gold(BG) instanton,” only for the Λ > 0 case. Because of this existence, thermodynamical stability of the system and the entropy bound are absent for Λ > 0, these being universal properties for Λ ≤ 0. In the second part, I investigate the thermodynamical properties of a gravity-scalar system with a φ2 potential. I show that when Λ ≤ 0 and the boundary value of scalar field Jφ is below some value, then the entropy bound and thermodynamical stability do exist. When either condition on the parameters does not hold, however, thermodynamical stability is (partially) broken. The properties of the system and the relation between BG instantons and the breakdown are discussed in detail.
Highlights
Partition function of gravity with the asymptotically flat boundary condition
Gravitational thermodynamics and gravitoscalar thermodynamics with S2 × R boundary geometry are investigated through the partition function, assuming that all Euclidean saddle point geometries contribute to the path integral and dominant ones are in the B3 × S1 or S2 × Disc topology sector
I show that when Λ ≤ 0 and the boundary value of scalar field Jφ is below some value, the entropy bound and thermodynamical stability do exist
Summary
Θ is the extrinsic curvature of ∂M and Θsub is the subtraction term needed for regularization in case on-shell actions diverge. It is not necessary for the analysis in this paper, for convenience I use it for setting the (free) energy of the ground states to zero. I concentrate only on the case that the boundary manifold has S2 × S1 topology and whose geometry is the product of a geometric 2-sphere and a circle This corresponds to the partition function of thermal equilibrium of a quantum spacetime whose boundary geometry is S2 × R. Throughout this paper, I assume all Euclidean saddle points in the minisuperspace contribute to the path integral.
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