A bstract We discuss a cosmological scenario where an effective violation of the strong energy condition (SEC) is realized through a coupling between SEC-fulfilling dark matter (DM) and dark energy (DE). Although the SEC-violating solutions might in principle last for an arbitrarily long time, we highlight several challenges that string realizations must face: most notably, these are the identification of suitable heavy states and their relationship with the theory cutoff. Furthermore, we discuss a black-hole argument that still allows for long-lived epochs of cosmic acceleration, but that prevents them from lasting forever. We also discuss negative potentials in the presence of a tower of light states, showing that the DM/DE coupling can push the theory towards regions of parametric control.
Shiu et al. (2026) studied this question.