Assessing the Robustness of the CPL Parametrization to Basis and Prior Variations: Insights from DESI DR2 BAO Data
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| Format: | Preprint |
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2025
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| author | Lee, Seokcheon |
| author_facet | Lee, Seokcheon |
| contents | 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), which separates the isotropic BAO scale from the scale-free Alcock-Paczynski ratio. We compare LambdaCDM, wCDM, and w_0w_aCDM models to evaluate how the choice of data basis and the width of the prior on w_a affect dark-energy inference. Ratio-only fits (D_M/D_H) amplify the (w_0, w_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) restore parameter consistency and show that these shifts mainly trace the degeneracy ridge. The pivoted equation of state, w_p = w(a_p) \simeq -0.9 \pm 0.1 at z_p \simeq 0.34, remains stable and consistent with a cosmological constant within 1sigma. Model-selection diagnostics (AIC, BIC, and Bayes factors) provide only moderate support for LambdaCDM, indicating no significant evidence for an evolving w(a). These findings clarify the interplay among basis choice, absolute-scale anchoring, and degeneracy geometry in BAO-only dark-energy analyses, providing a benchmark for future DESI and next-generation surveys. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2506_18230 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Assessing the Robustness of the CPL Parametrization to Basis and Prior Variations: Insights from DESI DR2 BAO Data Lee, Seokcheon Cosmology and Nongalactic Astrophysics 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), which separates the isotropic BAO scale from the scale-free Alcock-Paczynski ratio. We compare LambdaCDM, wCDM, and w_0w_aCDM models to evaluate how the choice of data basis and the width of the prior on w_a affect dark-energy inference. Ratio-only fits (D_M/D_H) amplify the (w_0, w_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) restore parameter consistency and show that these shifts mainly trace the degeneracy ridge. The pivoted equation of state, w_p = w(a_p) \simeq -0.9 \pm 0.1 at z_p \simeq 0.34, remains stable and consistent with a cosmological constant within 1sigma. Model-selection diagnostics (AIC, BIC, and Bayes factors) provide only moderate support for LambdaCDM, indicating no significant evidence for an evolving w(a). These findings clarify the interplay among basis choice, absolute-scale anchoring, and degeneracy geometry in BAO-only dark-energy analyses, providing a benchmark for future DESI and next-generation surveys. |
| title | Assessing the Robustness of the CPL Parametrization to Basis and Prior Variations: Insights from DESI DR2 BAO Data |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2506.18230 |