UV-complete and stable Quintom Dark Energy models in the light of DESI DR2

Abstract: We propose that Quintom dark energy, the simplest framework allowing crossing of the cosmological-constant boundary, admits a natural UV completion in a 5D anisotropic orbifold lattice: the Non-Perturbative Gauge-Higgs Unification (NPGHU) model. In this setup, a bulk 5D SU(2) gauge field projects on the 4D boundary to a complex scalar and a U(1) gauge field, identified with the dynamical dark-energy sector, while the Standard Model and dark matter remain localized in four dimensions. At late times, bulk-induced dimension-6 higher-derivative operators generate both physical and phantom scalar and gauge degrees of freedom. We show that the resulting 4D effective action is a modified Quintom model whose background equation of state can naturally realize Quintom-B behavior. A crucial contribution arises from the massive gauge ghost, allowing an excellent fit to DESI data with negligible fine-tuning, unlike standard Quintom scenarios. We further show that the inherited properties of the NPGHU construction e.g. absence of fundamental ghost instabilities, absence of potential terms and a finite low-energy cutoff $Λ$ associated with approximate Lorentz invariance, play a central role in the consistency of the effective theory under linear perturbations and vacuum decay. For the most natural regime, $Λ\approx {\cal O}(10)H_0$, the model remains robust despite the presence of IR phantom modes. Our results provide a natural and predictive framework in which Quintom dark energy can be consistently embedded in a fundamental theory.