Cosmological Analysis: Resolving the Hubble and S8 Tensions via Dynamical Dark Energy and Neutrino Mass

The persistent discrepancies between early-universe predictions and late-universe measurements
of the Hubble constant (H0 ) and the amplitude of matter fluctuations (S8 ) suggest a potential
breakdown of the standard ΛCDM cosmological model. In this paper, we present a comprehen-
sive MCMC analysis combining 8 primary datasets: Planck 2018, ACTPol DR4, DES Y1, BAO,
and Pantheon+ with SH0ES calibration. To rigorously test the ΛCDM framework without in-
troducing covariance from Cepheid calibrations, we subjected a Planck-locked ΛCDM baseline
(H0 = 67.4) to importance sampling using strictly independent late-time geometric and stellar
probes (TRGB, H0LiCOW, and Megamasers).
We find that the extended wνΛCDM model naturally converges to H0 = 70.04, driven
by a preference for phantom dark energy (w = −1.0641). This provides a near-perfect fit to
independent TRGB measurements while preserving structural harmony in the S8 regime via a
P
non-zero neutrino mass ( mν < 0.0962 eV at 95% CL, with a mean of 0.0915 eV). The locked
ΛCDM baseline suffers a catastrophic statistical failure across all late-universe probes, resulting
in a decisive model preference of ∆χ2 = 37.43 for the extended framework. This exceeds
the formal 5σ discovery threshold, providing robust evidence that dynamical dar