$H_0$ as a Universal FLRW Diagnostic

Krishnan, Chethan; Mondol, Ranjini

doi:10.48550/arxiv.2201.13384

Cited by 10 publications

(14 citation statements)

References 42 publications

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“…At a mundane level, simplifying assumptions are required to solve the Einstein equations, and once the FLRW symmetries are imposed and the energymomentum tensor associated with a homogeneous and isotropic cosmic perfect fluid specified, the Friedmann equations reduce to a first order ordinary differential equation with a unique integration constant, namely the Hubble constant H 0 . As a result, within the FLRW paradigm, H 0 is a universal constant parameter in any FLRW cosmological model [45,46]. Thus, the constancy of H 0 over the sky provides a handle for testing isotropy and hence FLRW cosmology; concretely, one can decompose the sky in hemispheres, or smaller patches, and directly compare H 0 inferences in different directions 31 .…”

Section: Prologuementioning

confidence: 99%

See 1 more Smart Citation

Is the observable Universe consistent with the cosmological principle?

Aluri

Cea

Chingangbam

et al. 2023

Class. Quantum Grav.

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The Cosmological Principle (CP) -- the notion that the Universe is spatially isotropic and homogeneous on large scales -- underlies a century of progress in cosmology. It is conventionally formulated through the Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) cosmologies as the spacetime metric, and culminates in the successful and highly predictive $\Lambda$-Cold-Dark-Matter ($\Lambda$CDM) model. Yet, tensions have emerged within the $\Lambda$CDM model, most notably a statistically significant discrepancy in the value of the Hubble constant, $H_0$. Since the notion of cosmic expansion determined by a single parameter is intimately tied to the CP, implications of the $H_0$ tension may extend beyond $\Lambda$CDM to the CP itself. This review surveys current observational hints for deviations from the expectations of the CP, highlighting synergies and disagreements that warrant further study. Setting aside the debate about individual large structures, potential deviations from the CP include variations of cosmological parameters on the sky, discrepancies in the cosmic dipoles, and mysterious alignments in quasar polarizations and galaxy spins. While it is possible that a host of observational systematics are impacting results, it is equally plausible that precision cosmology may have outgrown the FLRW paradigm, an extremely pragmatic but non-fundamental symmetry assumption.

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Section: Prologuementioning

confidence: 99%

“…31 In principle, this test can be performed with any cosmological parameter, but as explained, H 0 has a special or universal status. One can also test the constancy of H 0 in different redshift ranges, but this constitutes a test within FLRW (see [45,46]).…”

Section: Prologuementioning

confidence: 99%

Is the observable Universe consistent with the cosmological principle?

Aluri

Cea

Chingangbam

et al. 2023

Class. Quantum Grav.

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“…Observations at different redshifts have shown that H 0 evolves with effective (binned) redshift in the flat ΛCDM model [10][11][12][13][14][15][16][17] (see also [18]. If true, this behaviour is indicative of model breakdown [19,20].…”

Section: Introductionmentioning

confidence: 97%

Putting Flat $Λ$CDM In The (Redshift) Bin

Colgáin¹,

Sheikh-Jabbari²,

Solomon³

et al. 2022

Preprint

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Flat ΛCDM cosmology is specified by two constant fitting parameters in the late Universe, the Hubble constant H 0 and matter density (today) Ω m . Through fitting (H 0 , Ω m ) to mock ΛCDM simulations in redshift bins, we confirm that A := H 2 0 (1−Ω m ) and B := H 2 0 Ω m distributions spread and contract, respectively, with increasing bin redshift. Noting that A = H 2 0 − B, the spread in A and contraction in B corresponds to a spread in H 0 , and consequently in Ω m . Restricted to non-negative energy densities, A, B ≥ 0, the spread in A yields a 'pile up' around A = 0 or Ω m = 1. At even higher redshifts, further spreading flattens A and causes pile up near Ω m = 0. Thus, in generic higher redshift bins the Planck value Ω m ∼ 0.3 appears with low probability. We explore if observational Hubble data, Type Ia supernovae and standardisable quasars substantiate the features. We confirm that observed data exhibit an increasing Ω m (decreasing H 0 ) trend with increasing bin redshift and that such behaviour can arise randomly within the flat ΛCDM model with probability p = 0.0021 (3.1 σ).

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“…In some sense, ΛCDM may be a smart model that predicts its own demise, including a decreasing H 0 with redshift (see Refs. [30,31] for related comments). Given the universal confidence in SN cosmology, the outlined trends can be confirmed or refuted by simply increasing the number of high redshift (z ∼ 1) SN.…”

Section: Introductionmentioning

confidence: 99%

Revealing Intrinsic Flat $Λ$CDM Biases with Standardizable Candles

Colgáin,

Sheikh-Jabbari,

Solomon

et al. 2022

Preprint

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Emerging high redshift cosmological probes, in particular quasars (QSOs), show a preference for larger matter densities, Ω m ≈ 1, within the flat ΛCDM framework. Here, using the Risaliti-Lusso relation for standardizable QSOs, we demonstrate that the QSOs recover the same Planck-ΛCDM Universe as Type Ia supernovae (SN), Ω m ≈ 0.3 at lower redshifts 0 < z 0.7, before transitioning to an Einstein-de Sitter Universe (Ω m = 1) at higher redshifts z 1. We illustrate the same trend, namely increasing Ω m and decreasing H 0 with redshift, in SN but poor statistics prevent a definitive statement. We explain physically why the trend is expected in the flat ΛCDM cosmology, illustrate the intrinsic bias and non-Gaussian tails with mock Pantheon data, and identify a similar trend in BAO below z = 1. Our results highlight an intrinsic bias in the flat ΛCDM Universe, whereby Ω m increases, H 0 decreases and S 8 increases with effective redshift, thus providing a new perspective on ΛCDM tensions; even in a Planck-ΛCDM Universe the current tensions might have been expected.

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$H_0$ as a Universal FLRW Diagnostic

Cited by 10 publications

References 42 publications

Is the observable Universe consistent with the cosmological principle?

Is the observable Universe consistent with the cosmological principle?

Putting Flat $Λ$CDM In The (Redshift) Bin

Revealing Intrinsic Flat $Λ$CDM Biases with Standardizable Candles

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