Two model-independent methods applied to latest SN and BAO data find the cosmic distance duality relation consistent with observations within 1 sigma and no evidence of violation.
Jerk, snap, and the cosmological equation of state
6 Pith papers cite this work, alongside 625 external citations. Polarity classification is still indexing.
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abstract
Taylor expanding the cosmological equation of state around the current epoch is the simplest model one can consider that does not make any a priori restrictions on the nature of the cosmological fluid. Most popular cosmological models attempt to be ``predictive'', in the sense that once somea priori equation of state is chosen the Friedmann equations are used to determine the evolution of the FRW scale factor a(t). In contrast, a retrodictive approach might usefully take observational dataconcerning the scale factor, and use the Friedmann equations to infer an observed cosmological equation of state. In particular, the value and derivatives of the scale factor determined at the current epoch place constraints on the value and derivatives of the cosmological equation of state at the current epoch. Determining the first three Taylor coefficients of the equation of state at the current epoch requires a measurement of the deceleration, jerk, and snap -- the second, third, and fourth derivatives of the scale factor with respect to time. Higher-order Taylor coefficients in the equation of state are related to higher-order time derivatives of the scale factor. Since the jerk and snap are rather difficult to measure, being related to the third and fourth terms in the Taylor series expansion of the Hubble law, it becomes clear why direct observational constraints on the cosmological equation of state are so relatively weak; and are likely to remain weak for the foreseeable future.
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Gaia quasar proper motions show a significant quadrupole signal matching an axisymmetric Bianchi I anisotropy model, but the amplitude does not increase with redshift as the model requires and the inferred local shear exceeds expectations.
Cosmographic constraints from 106 FRBs on H0, q0, j0 depend sensitively on whether a Gaussian or quasi-Gaussian PDF is assumed for DM_IGM and on whether the baryon mass fraction is fixed or free.
A bias-controlled quasar sample of ~2000 objects demonstrates that the X-ray-to-UV luminosity relation remains constant from redshift 0.7 to 5.
Cosmographic Taylor and Padé models fitted to Pantheon+SH0ES+GRB+DESI BAO data yield redshift drift predictions compatible with ΛCDM and ω0ω1CDM at 1-2σ, with mock drift data tightening q0 and j0 bounds.
DESI data hint that dark energy evolves (w0>−1, wa<0, phantom crossing) at 2.5–4.2σ, but the same expansion history can also be produced by interacting dark sectors, modified gravity, or non-cold dark matter.
citing papers explorer
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Model-independent test of the cosmic distance duality relation with recent observational data
Two model-independent methods applied to latest SN and BAO data find the cosmic distance duality relation consistent with observations within 1 sigma and no evidence of violation.
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Mapping the Universe as a Bianchi I cosmology with Gaia data
Gaia quasar proper motions show a significant quadrupole signal matching an axisymmetric Bianchi I anisotropy model, but the amplitude does not increase with redshift as the model requires and the inferred local shear exceeds expectations.
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The impact of FRB dispersion measure probability distribution functions on cosmographic estimates
Cosmographic constraints from 106 FRBs on H0, q0, j0 depend sensitively on whether a Gaussian or quasi-Gaussian PDF is assumed for DM_IGM and on whether the baryon mass fraction is fixed or free.
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The X-ray-to-UV relation does not evolve in homogeneous quasar samples
A bias-controlled quasar sample of ~2000 objects demonstrates that the X-ray-to-UV luminosity relation remains constant from redshift 0.7 to 5.
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Mapping the redshift drift at various redshifts through cosmography
Cosmographic Taylor and Padé models fitted to Pantheon+SH0ES+GRB+DESI BAO data yield redshift drift predictions compatible with ΛCDM and ω0ω1CDM at 1-2σ, with mock drift data tightening q0 and j0 bounds.
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Dark Energy in the DESI Era: A Brief Review of Evidence, Beyond-$\Lambda$CDM Interpretations, and Tensions
DESI data hint that dark energy evolves (w0>−1, wa<0, phantom crossing) at 2.5–4.2σ, but the same expansion history can also be produced by interacting dark sectors, modified gravity, or non-cold dark matter.