Can coupled thawing quintessence reproduce DESI DR2? A test with two potentials
DESI DR2 favours dark energy whose equation of state evolves crossing $w=-1$ in the past. Coupled quintessence can produce such an apparent phantom crossing without a phantom field, since a coupled dark sector analysed under the assumption of separate conservation yields an effective equation of state below $-1$. We test whether this mechanism can reproduce the DESI result, using two thawing potentials, a cosine and a double-exponential hilltop, confronted with DESI DR2 BAO, Planck PR4 and three supernova compilations. Both models improve on $Λ$CDM by $Δχ^2 = 5$--$15$, recovering $64$--$92\%$ of the improvement achieved by $w_0w_a$CDM. They track the $w_0w_a$CDM equation of state at $z\lesssim0.4$ but cross the phantom divide later, near $z\simeq1$ rather than $z\simeq0.4$--$0.5$. The coupling is bounded at $|β|<0.073$ ($95\%$), and the two potentials agree on it to within $0.15σ$. They differ instead in the equation of state they can reach: the cosine comes closer to the evolution preferred by DESI and is weakly preferred by the fit. The coupling posterior is bimodal, with modes at $β\simeq\pm0.05$; only the negative mode produces the crossing, and it is the higher of the two in every analysis. In conclusion, the data favour the coupled quintessence phantom crossing but do not yet require it.