Fermion-condensate vacuum energy plus Buchert backreaction from nonlinear structure formation yields a low-redshift phantom crossing consistent with DESI+CMB+SNIa data for a chosen backreaction density.
Hubble parameter measurement constraints on the redshift of the deceleration-acceleration transition, dynamical dark energy, and space curvature
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abstract
We compile an updated list of 38 measurements of the Hubble parameter $H(z)$ between redshifts $0.07 \leq z \leq 2.36$ and use them to place constraints on model parameters of constant and time-varying dark energy cosmological models, both spatially flat and curved. We use five models to measure the redshift of the cosmological deceleration-acceleration transition, $z_{\rm da}$, from these $H(z)$ data. Within the error bars, the measured $z_{\rm da}$ are insensitive to the model used, depending only on the value assumed for the Hubble constant $H_0$. The weighted mean of our measurements is $z_{\rm da} = 0.72 \pm 0.05\ (0.84 \pm 0.03)$ for $H_0 = 68 \pm 2.8\ (73.24 \pm 1.74)$ km s$^{-1}$ Mpc$^{-1}$ and should provide a reasonably model-independent estimate of this cosmological parameter. The $H(z)$ data are consistent with the standard spatially-flat $\Lambda$CDM cosmological model but do not rule out non-flat models or dynamical dark energy models.
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DESI BAO+CMB yielding a positive present-day deceleration parameter q0≈0.10 (vs SDSS's q0≈−0.22) is explained by DESI's higher lowest effective redshift (0.295 vs 0.15), not by new physics.
The JCDM model yields H0 of 66.95 plus or minus 0.51 km/s/Mpc and Omega_m of 0.3419 plus or minus 0.0065 in a flat universe, rising to H0 of 69.13 plus or minus 0.56 with slight positive curvature, fitting late-time data but struggling with full early-universe consistency.
citing papers explorer
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Phantom crossing from the Standard Model and General Relativity
Fermion-condensate vacuum energy plus Buchert backreaction from nonlinear structure formation yields a low-redshift phantom crossing consistent with DESI+CMB+SNIa data for a chosen backreaction density.
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Present Day Cosmic Acceleration from SDSS and DESI BAO: A Call for Finer Tomography of the DESI Bright Galaxy Survey
DESI BAO+CMB yielding a positive present-day deceleration parameter q0≈0.10 (vs SDSS's q0≈−0.22) is explained by DESI's higher lowest effective redshift (0.295 vs 0.15), not by new physics.
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Cosmological constraints on the big bang quantum cosmology model
The JCDM model yields H0 of 66.95 plus or minus 0.51 km/s/Mpc and Omega_m of 0.3419 plus or minus 0.0065 in a flat universe, rising to H0 of 69.13 plus or minus 0.56 with slight positive curvature, fitting late-time data but struggling with full early-universe consistency.