Post-Newtonian celestial mechanics in scalar-tensor cosmology

Understand

Applying the recently developed dynamical perturbation formalism on cosmological background to scalar-tensor theory, we provide a solid theoretical basis and a rigorous justification for phenomenological models of orbital dynamics that are currently used to interpret experimental measurements of the time-dependent gravitational constant.

• We derive the field equations for the scalar-tensor perturbations and study their gauge freedom associated with the cosmological expansion.
• We find a new gauge eliminating a prohibitive number of gauge modes in the field equations and significantly simplifying post-Newtonian equations of motion for localized astronomical systems in the universe with time-dependent gravitational constant.
• We identify several new post-Newtonian terms and calculate their effect on secular cosmological evolution of the osculating orbital elements.