2026/07/29 by Paulo Montero-Camacho, Yi Mao
Physics and Astronomy · #astro-ph.CO
Comments welcome! 8 pages, 5 figures
arxiv created 2026/07/29 · arxiv updated 2026/07/30
Recent cosmological analyses combining high-redshift cosmic microwave background (CMB) measurements with low-redshift baryon acoustic oscillation (BAO) data have reported a preference for dynamical dark energy, with the cosmological constant scenario (ΛCDM) disfavored at the ∼ 3σ level. These analyses, however, typically rely on large-scale CMB polarization measurements to constrain the optical depth to reionization τ\rm reio∼ 0.06, raising the question of whether potential systematics in this dataset could influence the inferred cosmological preference. Excluding large-scale polarization data substantially weakens the tension with ΛCDM to the \lesssim 2σ level, nevertheless at a price of increasing τ\rm reio significantly to ∼ 0.09. Here, we use a physically motivated Gompertzian reionization framework to perform a self-consistent Bayesian analysis combining CMB (excluding large-scale polarization data), BAO, and independent measurements of the neutral hydrogen fraction evolution from quasar damping wing observations and dark pixel constraints. We derive τ\rm reio = 0.067 ± 0.011, in good agreement with cosmological analyses that would include large-scale CMB polarization data, while the inferred reionization history is consistent with multiple observational constraints. Our analysis recovers a preference for dynamical dark energy at the \gtrapprox2σ level. These results demonstrate that astrophysical probes of reionization independently recover the optical depth required by CMB polarization measurements, suggesting that potential systematics in large-scale polarization alone are unlikely to fully explain the emerging preference for dynamical dark energy.