A New Constraint on the Optical Depth from the Reionization History Independent of CMB Large-Scale E-Mode Polarization
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| Autores principales: | , , , , , , , |
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| Formato: | Preprint |
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2026
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| _version_ | 1866912824146526208 |
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| author | Kageura, Yuta Ouchi, Masami Naokawa, Fumihiro Umeda, Hiroya Matsumoto, Akinori Harikane, Yuichi Nakane, Minami Thai, Tran Thi |
| author_facet | Kageura, Yuta Ouchi, Masami Naokawa, Fumihiro Umeda, Hiroya Matsumoto, Akinori Harikane, Yuichi Nakane, Minami Thai, Tran Thi |
| contents | Recent studies report a mild discrepancy between baryon acoustic oscillation (BAO) and cosmic microwave background (CMB) measurements within the $Λ$CDM framework. This discrepancy could be explained if the optical depth $τ$ inferred from the CMB large-scale E-mode polarization is underestimated, which may be biased by foreground-subtraction or instrumental systematics. In this work, we present a determination of $τ$ independent of the large-scale E-mode polarization, using the latest measurements of the redshift evolution of the neutral hydrogen fraction $x_\mathrm{HI}(z)$, which is constrained by Lyman-$α$ forest and damping-wing absorption measurements at $z\sim5$-$14$, based on ground-based optical and JWST observations. Combining $x_\mathrm{HI}(z)$ with the Planck CMB power spectra excluding the large-scale E-mode polarization, we obtain $τ=0.0552^{+0.0019}_{-0.0026}$, a stringent constraint consistent with the previous CMB results including the large-scale E-mode. We also evaluate a potential systematic error in our method associated with absorption modeling, obtaining $τ=0.0552^{+0.0075}_{-0.0049}$. Using this constraint on $τ$, we resolve the degeneracy in the $τ$-$Ω_m$ plane and find a $2.4σ$ tension with the DESI DR2 BAO results, thereby confirming the claimed mild discrepancy suggestive of physics beyond $Λ$CDM. Finally, we derive an upper limit on the sum of neutrino masses, $Σm_ν<0.0550\,(0.0717)$ eV at the 95% (99%) confidence level. This limit favors the normal mass ordering and, when combined with the lower limits from neutrino oscillation experiments, yields a further constraint, $Σm_ν=0.0594_{-0.0007}^{+0.0113}$ eV. However, the cosmological upper limit and the oscillation-based lower limit show a mild $2.2σ$ tension, providing an independent indication of possible physics beyond $Λ$CDM. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_09644 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | A New Constraint on the Optical Depth from the Reionization History Independent of CMB Large-Scale E-Mode Polarization Kageura, Yuta Ouchi, Masami Naokawa, Fumihiro Umeda, Hiroya Matsumoto, Akinori Harikane, Yuichi Nakane, Minami Thai, Tran Thi Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies Recent studies report a mild discrepancy between baryon acoustic oscillation (BAO) and cosmic microwave background (CMB) measurements within the $Λ$CDM framework. This discrepancy could be explained if the optical depth $τ$ inferred from the CMB large-scale E-mode polarization is underestimated, which may be biased by foreground-subtraction or instrumental systematics. In this work, we present a determination of $τ$ independent of the large-scale E-mode polarization, using the latest measurements of the redshift evolution of the neutral hydrogen fraction $x_\mathrm{HI}(z)$, which is constrained by Lyman-$α$ forest and damping-wing absorption measurements at $z\sim5$-$14$, based on ground-based optical and JWST observations. Combining $x_\mathrm{HI}(z)$ with the Planck CMB power spectra excluding the large-scale E-mode polarization, we obtain $τ=0.0552^{+0.0019}_{-0.0026}$, a stringent constraint consistent with the previous CMB results including the large-scale E-mode. We also evaluate a potential systematic error in our method associated with absorption modeling, obtaining $τ=0.0552^{+0.0075}_{-0.0049}$. Using this constraint on $τ$, we resolve the degeneracy in the $τ$-$Ω_m$ plane and find a $2.4σ$ tension with the DESI DR2 BAO results, thereby confirming the claimed mild discrepancy suggestive of physics beyond $Λ$CDM. Finally, we derive an upper limit on the sum of neutrino masses, $Σm_ν<0.0550\,(0.0717)$ eV at the 95% (99%) confidence level. This limit favors the normal mass ordering and, when combined with the lower limits from neutrino oscillation experiments, yields a further constraint, $Σm_ν=0.0594_{-0.0007}^{+0.0113}$ eV. However, the cosmological upper limit and the oscillation-based lower limit show a mild $2.2σ$ tension, providing an independent indication of possible physics beyond $Λ$CDM. |
| title | A New Constraint on the Optical Depth from the Reionization History Independent of CMB Large-Scale E-Mode Polarization |
| topic | Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2601.09644 |