S-dual Quintessence, the Swampland, and the DESI DR2 Results

We propose a dark energy model in which a quintessence field φ rolls near the vicinity of a local maximum of its potential characterized by the simplest S self-dual form V(φ) = Λ \ sech(√2 \, φ/Mₚ), where Mₚ is the reduced Planck mass and Λ ~ 10⁻¹²⁰ Mₚ⁴ is the cosmological constant. We confront the model with Swampland ideas and show that the S-dual potential is consistent with the distance conjecture, the de Sitter conjecture, and the trans-Planckian censorship conjecture. We also examine the compatibility of this phenomenological model with the intriguing DESI DR2 results and show that the shape of the S-dual potential is almost indistinguishable from the axion-like potential, V (φ) = mₐ² \ fₐ² \ [ 1 + cos(φ/fₐ)], with mₐ and fₐ parameters fitted by the DESI Collaboration to accommodate the DR2 data. The self-dual potential has the advantage that one starts at the self-dual point and this is a theoretical motivation, because as the universe cools off the Z₂ symmetry gets broken leading to a natural rolling away from the symmetric point.