I discuss how one can apply the covariant formalism developed by Vilkovisky
and DeWitt to obtain frame invariant fifth force calculations for scalar-tensor
theories. Fifth forces are severely constrained by astrophysical measurements.
It was shown previously that for scale-invariant Higgs-dilaton gravity, in a
particular choice of Jordan frame, the dilaton fifth force is dramatically
suppressed, evading the observational constraints. Using a geometric approach I
extend this result to all frames, and show that the usual dichotomy of “Jordan
frame” versus “Einstein frame” is better understood as a continuum of frames:
submanifold slices of a more general field space.
