Λ_s VCDM is a predictive model combining Λ_s CDM with VCDM gravity via an auxiliary scalar field and sigmoid-smoothed potentials to enable stable mirror AdS-to-dS transitions with possible transient acceleration.
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Evolution of dark energy reconstructed from the latest observations
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abstract
We reconstruct evolution of the dark energy (DE) density using a nonparametric Bayesian approach from a combination of latest observational data. We caution against parameterizing DE in terms of its equation of state as it can be singular in modified gravity models, and using it introduces a bias preventing negative effective DE densities. We find a $3.7\sigma$ preference for an evolving effective DE density with interesting features. For example, it oscillates around the $\Lambda$CDM prediction at $z\lesssim0.7$, and could be negative at $z\gtrsim2.3$; dark energy can be pressure-less at multiple redshifts, and a short period of cosmic deceleration is allowed at $0.1 \lesssim z\lesssim 0.2$. We perform the reconstruction for several choices of the prior, as well as a evidence-weighted reconstruction. We find that some of the dynamical features, such as the oscillatory behaviour of the DE density, are supported by the Bayesian evidence, which is a first detection of a dynamical DE with a positive Bayesian evidence. The evidence-weighted reconstruction prefers a dynamical DE at a $(2.5\pm0.06)\sigma$ significance level.
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Relativistic N-body simulations of Lambda_s CDM produce a redshift-dependent crest in the matter power spectrum ratio, peaking at 20-25% near the transition and leaving a 15-20% uplift at z=0 on group scales.
A sign-switching dark energy model (Λ_s CDM) recovers positive effective neutrino masses (0.055 ± 0.050 eV) consistent with oscillation data, unlike ΛCDM which prefers negative values (-0.075 eV), for DESI DR2 + CMB + supernova fits with z_† > 2.4.
Node-based reconstruction of cosmic expansion prefers stronger deceleration at z≈1.7 than smooth DE EoS parametrizations, isolating z~1.5-2 as a window where the latter may compress localized kinematic features permitted by current data.
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.
DESI DR2 BAO combined with Pantheon+, DES-Dovekie and Union3 supernovae yields 1.1-2.3 sigma preference for Quintom-B type evolving dark energy (w0 > -1, wa < 0) with phantom crossing near z ~ 0.5, but no model reaches robust statistical significance.
This review traces the history of dynamical dark energy, presents the no-go theorem against single-field crossing of w = -1, and surveys viable Quintom constructions including multi-field models and modified gravity in light of DESI DR2 hints.
A review summarizing the Hubble constant tension and proposed solutions from new physics that restore agreement between Planck CMB data and local H0 measurements within 1-2 sigma.
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$\Lambda_{\rm s}$CDM cosmology from a type-II minimally modified gravity
Λ_s VCDM is a predictive model combining Λ_s CDM with VCDM gravity via an auxiliary scalar field and sigmoid-smoothed potentials to enable stable mirror AdS-to-dS transitions with possible transient acceleration.
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Nonlinear Matter Power Spectrum from relativistic $N$-body Simulations: $\Lambda_{\rm s}$CDM versus $\Lambda$CDM
Relativistic N-body simulations of Lambda_s CDM produce a redshift-dependent crest in the matter power spectrum ratio, peaking at 20-25% near the transition and leaving a 15-20% uplift at z=0 on group scales.
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Negative neutrino mass or negative dark energy?
A sign-switching dark energy model (Λ_s CDM) recovers positive effective neutrino masses (0.055 ± 0.050 eV) consistent with oscillation data, unlike ΛCDM which prefers negative values (-0.075 eV), for DESI DR2 + CMB + supernova fits with z_† > 2.4.
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Do equation of state parametrizations of dark energy faithfully capture the dynamics of the late universe?
Node-based reconstruction of cosmic expansion prefers stronger deceleration at z≈1.7 than smooth DE EoS parametrizations, isolating z~1.5-2 as a window where the latter may compress localized kinematic features permitted by current data.
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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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Evidence for evolving dark energy from DESI DR2 BAO and Pantheon$^+$, DES-Dovekie, and Union3
DESI DR2 BAO combined with Pantheon+, DES-Dovekie and Union3 supernovae yields 1.1-2.3 sigma preference for Quintom-B type evolving dark energy (w0 > -1, wa < 0) with phantom crossing near z ~ 0.5, but no model reaches robust statistical significance.
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The Quintom theory of dark energy after DESI DR2
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