Colloquium on May. 28, 2026

ΛCDM will not be rescued by a high optical depth

Speaker: Paulo Montero-Camacho (Peng Cheng Laboratory)

Venue: SWIFAR Building 2111

Time: 16:00 PM, Thursday, May. 28, 2026

Abstract:

Recent BAO and Type Ia supernovae measurements have indicated a growing preference for evolving dark energy, challenging the standard ΛCDM model. This trend appears to be worsening as new data releases from DESI add to the tension. Simultaneously, the 2-sigma cosmological constraint on the sum of the neutrino masses is starting to show discrepancy with oscillation experiments. To resolve these tensions, it has recently been proposed by two independent groups that unknown systematics might affect low-ℓ CMB polarization data as omitting this dataset shifts the optical depth to a higher value (τ ≈ 0.09), which appears to resolve the tension with ΛCDM and relax the neutrino mass bounds. In this talk, I demonstrate that such high τ values are in significant conflict with independent epoch of reionization (EoR) observations, which are in agreement with low-ℓ CMB polarization measurements. Furthermore, I show that a joint analysis excluding low-ℓ polarization but incorporating EoR data fails to recover τ ≈ 0.09, suggesting that neglecting low-ℓ CMB polarization is insufficient to resolve the current ΛCDM crisis.