Cosmological backreaction in spherical and plane symmetric dust-filled space-times

Clifton, Timothy; Sussman, Roberto A.

doi:10.1088/1361-6382/ab3a14

Cited by 12 publications

(12 citation statements)

References 26 publications

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“…Inhomogeneities back-react on the large scale metric to produce an effective stress-energy tensor that adds up to the large scale stress-energy tensor. Different studies that attempt to assess the magnitude of such a backreaction of local structure on large scale cosmological dynamics reach conflicting results [172,173], with the discrepancy being partly due to the differences in the quantification of backreaction in the different schemes [174]. Various frameworks for investigating the fitting problem have been proposed, see e.g.…”

Section: Inhomogeneous and Anisotropic Solutionsmentioning

confidence: 99%

In the realm of the Hubble tension—a review of solutions ^*

Valentino

Mena²,

Pan³

et al. 2021

Class. Quantum Grav.

1,426

760

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The simplest ΛCDM model provides a good fit to a large span of cosmological data but harbors large areas of phenomenology and ignorance. With the improvement of the number and the accuracy of observations, discrepancies among key cosmological parameters of the model have emerged. The most statistically significant tension is the 4σ to 6σ disagreement between predictions of the Hubble constant, H 0, made by the early time probes in concert with the ‘vanilla’ ΛCDM cosmological model, and a number of late time, model-independent determinations of H 0 from local measurements of distances and redshifts. The high precision and consistency of the data at both ends present strong challenges to the possible solution space and demands a hypothesis with enough rigor to explain multiple observations—whether these invoke new physics, unexpected large-scale structures or multiple, unrelated errors. A thorough review of the problem including a discussion of recent Hubble constant estimates and a summary of the proposed theoretical solutions is presented here. We include more than 1000 references, indicating that the interest in this area has grown considerably just during the last few years. We classify the many proposals to resolve the tension in these categories: early dark energy, late dark energy, dark energy models with 6 degrees of freedom and their extensions, models with extra relativistic degrees of freedom, models with extra interactions, unified cosmologies, modified gravity, inflationary models, modified recombination history, physics of the critical phenomena, and alternative proposals. Some are formally successful, improving the fit to the data in light of their additional degrees of freedom, restoring agreement within 1–2σ between Planck 2018, using the cosmic microwave background power spectra data, baryon acoustic oscillations, Pantheon SN data, and R20, the latest SH0ES Team Riess, et al (2021 Astrophys. J. 908 L6) measurement of the Hubble constant (H 0 = 73.2 ± 1.3 km s−1 Mpc−1 at 68% confidence level). However, there are many more unsuccessful models which leave the discrepancy well above the 3σ disagreement level. In many cases, reduced tension comes not simply from a change in the value of H 0 but also due to an increase in its uncertainty due to degeneracy with additional physics, complicating the picture and pointing to the need for additional probes. While no specific proposal makes a strong case for being highly likely or far better than all others, solutions involving early or dynamical dark energy, neutrino interactions, interacting cosmologies, primordial magnetic fields, and modified gravity provide the best options until a better alternative comes along.

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Section: Inhomogeneous and Anisotropic Solutionsmentioning

confidence: 99%

In the realm of the Hubble tension—a review of solutions ^*

Valentino

Mena²,

Pan³

et al. 2021

Class. Quantum Grav.

1,426

760

View full text Add to dashboard Cite

show abstract

“…A necessary condition of integrability of equation (3.32) to yield equation (3.33) is given by the relation: 37) where the source part on the right-hand side satisfies the averaged energy conservation law:…”

Section: Theorem 1b (Integrability and Energy Balance Conditions)mentioning

confidence: 99%

“…Such effective relations encode inhomogeneous properties and evolution details of the fluid and, hence, they are dynamical and not simply derivable from thermodynamical properties. Closure conditions can be studied in terms of exact scaling solutions [22,28,79], global assumptions on model universes [20,21], exact solutions of the Einstein equations [64,10,83,84,63,85,35,11,86,37] (see also [23, sect.7]), or generic but approximate models for inhomogeneities. The latter may be based on relativistic Lagrangian perturbation theory, e.g.…”

Section: Is There Interest To Go Beyond This Work? -An Outlookmentioning

confidence: 99%

On average properties of inhomogeneous fluids in general relativity III: general fluid cosmologies

2020

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We investigate effective equations governing the volume expansion of spatially averaged portions of inhomogeneous cosmologies in spacetimes filled with an arbitrary fluid. This work is a follow-up to previous studies focused on irrotational dust models (Paper I) and irrotational perfect fluids (Paper II) in floworthogonal foliations of spacetime. It complements them by considering arbitrary foliations, arbitrary lapse and shift, and by allowing for a tilted fluid flow with vorticity. As for the first studies, the propagation of the spatial averaging domain is chosen to follow the congruence of the fluid, which avoids unphysical dependencies in the averaged system that is obtained. We present two different averaging schemes and corresponding systems of averaged evolution equations providing generalizations of Papers I and II. The first one retains the averaging operator used in several other generalizations found in the literature. We extensively discuss relations to these formalisms and pinpoint limitations, in particular regarding rest mass conservation on the averaging domain. The alternative averaging scheme that we subsequently introduce follows the spirit of Papers I and II and focuses on the fluid flow and the associated 1 + 3 threading congruence, used jointly with the 3 + 1 foliation that builds the surfaces of averaging. This results in compact averaged equations with a minimal number of cosmological backreaction terms. We highlight that this system becomes especially transparent when applied to a natural class of foliations which have constant fluid proper time slices.

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“…A broader representation of their work can be found in these two reviews [243,244] See also [245,246].…”

Section: Backreaction Of Inhomogeneous Mode In Classical Grmentioning

confidence: 99%

Weyl Curvature Hypothesis in Light of Quantum Backreaction at Cosmological Singularities or Bounces

2021

Universe

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The Weyl curvature constitutes the radiative sector of the Riemann curvature tensor and gives a measure of the anisotropy and inhomogeneities of spacetime. Penrose’s 1979 Weyl curvature hypothesis (WCH) assumes that the universe began at a very low gravitational entropy state, corresponding to zero Weyl curvature, namely, the Friedmann–Lemaître–Robertson–Walker (FLRW) universe. This is a simple assumption with far-reaching implications. In classical general relativity, Belinsky, Khalatnikov and Lifshitz (BKL) showed in the 70s that the most general cosmological solutions of the Einstein equation are that of the inhomogeneous Kasner types, with intermittent alteration of the one direction of contraction (in the cosmological expansion phase), according to the mixmaster dynamics of Misner (M). How could WCH and BKL-M co-exist? An answer was provided in the 80s with the consideration of quantum field processes such as vacuum particle creation, which was copious at the Planck time (10−43 s), and their backreaction effects were shown to be so powerful as to rapidly damp away the irregularities in the geometry. It was proposed that the vaccum viscosity due to particle creation can act as an efficient transducer of gravitational entropy (large for BKL-M) to matter entropy, keeping the universe at that very early time in a state commensurate with the WCH. In this essay I expand the scope of that inquiry to a broader range, asking how the WCH would fare with various cosmological theories, from classical to semiclassical to quantum, focusing on their predictions near the cosmological singularities (past and future) or avoidance thereof, allowing the Universe to encounter different scenarios, such as undergoing a phase transition or a bounce. WCH is of special importance to cyclic cosmologies, because any slight irregularity toward the end of one cycle will generate greater anisotropy and inhomogeneities in the next cycle. We point out that regardless of what other processes may be present near the beginning and the end states of the universe, the backreaction effects of quantum field processes probably serve as the best guarantor of WCH because these vacuum processes are ubiquitous, powerful and efficient in dissipating the irregularities to effectively nudge the Universe to a near-zero Weyl curvature condition.

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Cosmological backreaction in spherical and plane symmetric dust-filled space-times

Cited by 12 publications

References 26 publications

In the realm of the Hubble tension—a review of solutions ^*

In the realm of the Hubble tension—a review of solutions ^*

On average properties of inhomogeneous fluids in general relativity III: general fluid cosmologies

Weyl Curvature Hypothesis in Light of Quantum Backreaction at Cosmological Singularities or Bounces

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Cosmological backreaction in spherical and plane symmetric dust-filled space-times

Cited by 12 publications

References 26 publications

In the realm of the Hubble tension—a review of solutions *

In the realm of the Hubble tension—a review of solutions *

On average properties of inhomogeneous fluids in general relativity III: general fluid cosmologies

Weyl Curvature Hypothesis in Light of Quantum Backreaction at Cosmological Singularities or Bounces

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Product

Resources

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In the realm of the Hubble tension—a review of solutions ^*

In the realm of the Hubble tension—a review of solutions ^*