No fifth force in a scale invariant universe
  We revisit the possibility that the Planck mass is spontaneously generated in
scale invariant scalar-tensor theories of gravity, typically leading to a
"dilaton." The fifth force, arising from the dilaton, is severely constrained
by astrophysical measurements. We explore the possibility that nature is
fundamentally Weyl-scale invariant and argue that, as a consequence, the fifth
force effects are dramatically suppressed and such models are viable. We
discuss possible obstructions to maintaining scale invariance and how these
might be resolved.
