Nonlocal dilaton coupling to dark matter: Cosmic acceleration and pressure backreaction

A model of nonlocal dilaton interactions, motivated by string duality symmetries, is applied to a scenario of "coupled quintessence" in which the dilaton dark energy is nonlocally coupled to the dark-matter sources. It is shown that the nonlocal effects tend to generate a backreaction which-for strong enough coupling-can automatically compensate the acceleration due to the negative pressure of the dilaton potential, thus asymptotically restoring the standard (dust-dominated) decelerated regime. This result is illustrated by analytical computations and numerical examples.