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We study the effects of coupling a cosmologically rolling scalar field tohigher order curvature terms. We show that when the strong coupling scale ofthe theory is on the 10^{-3}-10^{-1}eV range, the model passes all experimentalbounds on the existence of fifth forces even if the field has a mass of theorder of the Hubble scale in vacuum and non-suppressed couplings to SM fields.The reason is that the coupling to certain curvature invariant acts as aneffective mass that grows in regions of large curvature. This prevents thefield from rolling down its potential near sources and makes its effects onfifth-force search experiments performed in the laboratory to be observableonly at the sub-mm scale. We obtain the static spherically symmetric solutionsof the theory and show that a long-range force appears but it is turned on onlybelow a fixed Newtonian acceleration scale of the order of the Hubble constant.We comment on the possibility of using this feature of the model to alleviatethe CDM small scale crisis and on its possible relation to MOND.

Dark Energy, scalar-curvature couplings and a critical acceleration scale