Recent measurements of baryon acoustic oscillations by the Dark Energy Spectroscopic Instrument (DESI) appear to indicate the existence of dynamical dark energy, such that parametrized reconstructions of its equation of state (EOS) exhibit a crossing of the phantom divide. In this paper, we study a field-theory model for an interacting dark sector, in which fermionic dark matter is coupled via a Yukawa interaction to a tachyonic scalar field dark energy governed by Born-Infeld dynamics. We demonstrate that this model naturally allows the effective EOS associated with the tachyonic dark energy component to undergo a double effective crossing of the phantom divide, while the intrinsic EOS of that dark component remains within the nonphantom regime. We test our model against baryon acoustic oscillation data from the DESI (Data Release 2) survey, as well as Planck 2018 cosmic microwave background distance priors and the most recent type Ia supernova compilations, obtaining robust constraints for the various data combinations considered. Furthermore, we identify statistically allowed trajectories within the posterior regions that cross the phantom divide twice. The model also predicts an ultralight mass for the fermionic dark matter particle on the order of $1.9\times {10}^{-3}\mathrm{eV}$, a result that points to a possible connection with new light particles in the dark sector and motivates future research incorporating cosmological perturbations.

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• Cosmology
• Dark energy
• Dark matter