Assessing the robustness of the CPL parametrization to basis and prior variations: insights from DESI DR2 BAO data

Abstract This work reexamines cosmological parameter constraints from the DESI Data Release 2 baryon acoustic oscillation (BAO) measurements using the distance-basis representation $$(D_V/r_d,\,D_M/D_H)$$ ( D V / r d , D M / D H ) , which separates the isotropic BAO scale from the scale-free Alcock–Paczynski ratio. This work compares $$\Lambda $$ Λ CDM, $$\omega \textrm{CDM}$$ ω CDM , and $$\omega _{0}\omega _{a}\textrm{CDM}$$ ω 0 ω a CDM models to evaluate how the choice of data basis and the width of the prior on $$\omega _a$$ ω a affect dark-energy inference. Ratio-only fits ( $$D_M/D_H$$ D M / D H ) amplify the $$(\omega _0,\,\omega _a)$$ ( ω 0 , ω a ) degeneracy and can produce large apparent shifts in point estimates without genuine evidence for dynamical dark energy. Joint fits using $$(D_V/r_d, D_M/D_H)$$ ( D V / r d , D M / D H ) restore parameter consistency and show that these shifts mainly trace the degeneracy ridge. The pivoted equation of state, $$\omega _p=\omega (a_p)\simeq -0.9\pm 0.1$$ ω p = ω ( a p ) ≃ - 0.9 ± 0.1 at $$z_p\simeq 0.34$$ z p ≃ 0.34 , remains stable and