No fifth force in a scale invariant universe

TL;DR

This paper investigates scale invariant scalar-tensor theories of gravity, proposing that Weyl-scale invariance suppresses fifth force effects, making such models compatible with astrophysical constraints.

Contribution

It demonstrates that Weyl-scale invariance can naturally suppress fifth forces in scalar-tensor theories, offering a viable alternative to models with a spontaneously generated Planck mass.

Findings

Fifth force effects are significantly suppressed in Weyl-scale invariant models

Scale invariance can be maintained despite potential obstructions

Such models remain consistent with astrophysical constraints

Abstract

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.