The Tolman-Ehrenfest criterion of thermal equilibrium in scalar-tensor gravity

The Tolman-Ehrenfest criterion for the thermal equilibrium of a fluid at rest in a static general-relativistic geometry is generalized to scalar-tensor gravity. Surprisingly, the gravitational scalar field, which fixes the strength of the effective gravitational coupling, does not play a role in determining thermal equilibrium. As a result, heat does not sink more in a gravitational field where gravity is stronger.
Comment: Conclusions changed, explanation and bibliography expanded. Matches version to appear in EPJC