To CPL, or not to CPL? What we have not learned about the dark energy equation of state
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| Format: | Preprint |
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2025
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| _version_ | 1866910898123177984 |
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| author | Nesseris, Savvas Akrami, Yashar Starkman, Glenn D. |
| author_facet | Nesseris, Savvas Akrami, Yashar Starkman, Glenn D. |
| contents | We show that using a Taylor expansion for the dark energy equation-of-state parameter and limiting it to the zeroth and first-order terms, i.e., the so-called Chevallier-Polarski-Linder (CPL) parametrization, instead of allowing for higher-order terms and then marginalizing over them, adds extra information not present in the data and leads to markedly different and potentially misleading conclusions. Fixing the higher-order terms to zero, one concludes that vacuum energy that is currently non-dynamical (e.g., the cosmological constant) is excluded at several $σ$ significance as the explanation of cosmic acceleration, even in Dark Energy Spectroscopic Survey (DESI) DR1 data. Meanwhile, instead marginalizing over the higher-order terms shows that we know neither the current dark energy equation of state nor its current rate of change well enough to make such a claim. This issue has become more prominent now with the recent release of high-quality Stage IV galaxy survey data. The results of analyses using simple Taylor expansions should be interpreted with great care. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2503_22529 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | To CPL, or not to CPL? What we have not learned about the dark energy equation of state Nesseris, Savvas Akrami, Yashar Starkman, Glenn D. Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology High Energy Physics - Phenomenology High Energy Physics - Theory We show that using a Taylor expansion for the dark energy equation-of-state parameter and limiting it to the zeroth and first-order terms, i.e., the so-called Chevallier-Polarski-Linder (CPL) parametrization, instead of allowing for higher-order terms and then marginalizing over them, adds extra information not present in the data and leads to markedly different and potentially misleading conclusions. Fixing the higher-order terms to zero, one concludes that vacuum energy that is currently non-dynamical (e.g., the cosmological constant) is excluded at several $σ$ significance as the explanation of cosmic acceleration, even in Dark Energy Spectroscopic Survey (DESI) DR1 data. Meanwhile, instead marginalizing over the higher-order terms shows that we know neither the current dark energy equation of state nor its current rate of change well enough to make such a claim. This issue has become more prominent now with the recent release of high-quality Stage IV galaxy survey data. The results of analyses using simple Taylor expansions should be interpreted with great care. |
| title | To CPL, or not to CPL? What we have not learned about the dark energy equation of state |
| topic | Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology High Energy Physics - Phenomenology High Energy Physics - Theory |
| url | https://arxiv.org/abs/2503.22529 |