Copernican Paradigm beyond FLRW

Krishnan, Chethan; Mondol, Ranjini; Sheikh-Jabbari, M. M.

doi:10.3390/sym15020428

“…These results are in some tension with previous studies based on the previous Pantheon sample [47]. The isotropy of H 0 has also been investigated using the hemisphere comparizon method [22,42,[48][49][50][51][52] and relatively small but statistically significant anisotropy level was identified in the direction of the CMB dipole. Since there is degeneracy between H 0 and the SnIa absolute magnitude a possible anisotropy in the best fit value of H 0 is probably connected with an anisotropy of the SnIa absolute magnitudes.…”

Section: Introductionsupporting

confidence: 77%

On the homogeneity of SnIa absolute magnitude in the Pantheon+ sample

Perivolaropoulos

¹

,

Skara

²

2023

Monthly Notices of the Royal Astronomical Society

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We have analysed the Pantheon+ sample using a new likelihood model that replaces the single SnIa absolute magnitude parameter M used in the standard likelihood model of Brout et. al. (2022) with two absolute magnitude parameters M<, M> and a transition distance dcrit that determines the distance at which M changes from M< to M>. The use of this likelihood dramatically changes the quality of fit to the Pantheon+ sample for a ΛCDM background by Δχ2 = −19.6. The tension between the M< and M> best fit values is at a level more than 3σ with a best fit dcrit very close to 20 Mpc. The origin of this improvement of fit and M< − M> tension is that the new likelihood model, successfully models two signals hidden in the data: 1. The volumetric redshift scatter bias systematic and 2. A mild signal for a change of intrinsic SnIa luminosity at about 20 Mpc. This interpretation of the results is confirmed by truncating the z < 0.01 Hubble diagram data from the Pantheon+ data where the above systematic is dominant and showing that the M< − M> tension decreases from above 3σ to a little less than 2σ. It is also confirmed by performing a Monte Carlo simulation which shows that the maximum significance of the SnIa luminosity transition ($\Sigma \equiv \frac{|M_>-M_<|}{\sqrt{\sigma _{M_>}^2+\sigma _{M_<}^2}}$) in the real data, is larger than the corresponding maximum significance of $94{{\%}}$ of the corresponding homogeneous simulated samples.

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“…These anisotropic solutions are an extension of the corresponding homogeneous and isotropic ones, and when parameter σ(t) tends to zero, anisotropy disappears. It is worth noting that anisotropic cosmological solutions may be important not only for research of space-time dynamics at early stage of the Universe but also at late cosmic scales in the framework of dipole cosmology 18 with evidence of some dipole anisotropy, what may have implications for the currently debated cosmic tensions (including H 0 ).…”

Section: Discussionmentioning

confidence: 99%

Nonlocal de Sitter gravity and its exact cosmological solutions

Dimitrijevic

¹

,

Драгович

²

,

Rakic

³

et al. 2022

J. High Energ. Phys.

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This paper is devoted to a simple nonlocal de Sitter gravity model and its exact vacuum cosmological solutions. In the Einstein-Hilbert action with Λ term, we introduce nonlocality by the following way: $$ R-2\Lambda =\sqrt{R-2\Lambda}\kern1em \sqrt{R-2\Lambda}\to \sqrt{R-2\Lambda}\kern1em F\left(\square \right)\kern1em \sqrt{R-2\Lambda} $$ R − 2 Λ = R − 2 Λ R − 2 Λ → R − 2 Λ F □ R − 2 Λ , where $$ F\left(\square \right)=1+{\sum}_{n=1}^{+\infty}\left({f}_n{\square}^n+{f}_{-n}{\square}^{-n}\right) $$ F □ = 1 + ∑ n = 1 + ∞ f n □ n + f − n □ − n is an analytic function of the d’Alembert-Beltrami operator □ and its inverse □−1. By this way, R and Λ enter with the same form into nonlocal version as they are in the local one, and nonlocal operator F(□) is dimensionless. The corresponding equations of motion for gravitational field gμν are presented. The first step in finding some exact cosmological solutions is solving the equation $$ \square \sqrt{R-2\Lambda}=q\sqrt{R-2\Lambda} $$ □ R − 2 Λ = q R − 2 Λ , where q = ζΛ (ζ ∈ R) is an eigenvalue and $$ \sqrt{R-2\Lambda} $$ R − 2 Λ is an eigenfunction of the operator □. We presented and discussed several exact cosmological solutions for homogeneous and isotropic universe. One of these solutions mimics effects that are usually assigned to dark matter and dark energy. Some other solutions are examples of the nonsingular bounce ones in flat, closed and open universe. There are also singular and cyclic solutions. All these cosmological solutions are a result of nonlocality and do not exist in the local de Sitter case.

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“…These two kinds of hair are in general nonlinearly coupled, and yet one is able to make statements about late time dynamics: the cosmic fluid hair can grow while the geometric hair is cut short. Our analysis [39] shows that FLRW geometries with a positive cosmological constant may be unstable against tilt perturbations, even though they may be stable against shear perturbations (as expected from cosmic no-hair theorem).…”

Section: Concluding Remarks and Outlookmentioning

confidence: 55%

“…The comparison between the two shows that the former always has a definite negative sign while the latter can change sign -this is the basis of the different dynamics of σ and β. The above discussions can set the stage for a refinement of the cosmic (no-)hair theorem, in tilted cosmologies [39]. We have a background "geometric hair" (the shear σ) and a "cosmic fluid hair" (the tilt β).…”

Section: Concluding Remarks and Outlookmentioning

confidence: 98%

Dipole cosmology: the Copernican paradigm beyond FLRW

Krishnan

¹

,

Mondol

²

,

Sheikh-Jabbari

³

2023

J. Cosmol. Astropart. Phys.

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We introduce the dipole cosmological principle, the idea that the Universe is a maximally Copernican cosmology, compatible with a cosmic flow. It serves as the most symmetric paradigm that generalizes the FLRW ansatz, in light of the increasingly numerous (but still tentative) hints that have emerged in the last two decades for a non-kinematic component in the CMB dipole. Einstein equations in our “dipole cosmology” are still ordinary differential equations — but instead of the two Friedmann equations, now we have four. The two new functions can be viewed as an anisotropic scale factor that breaks the isotropy group from SO(3) to U(1), and a “tilt” that captures the cosmic flow velocity. The result is an axially isotropic, tilted Bianchi V/VII_h cosmology. We assess the possibility of model building within the dipole cosmology paradigm, and discuss the dynamics of expansion rate, anisotropic shear and tilt, in various examples. A key observation is that the cosmic flow (tilt) can grow even while the anisotropy (shear) dies down. Remarkably, this can happen even in an era of late time acceleration.

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Copernican Paradigm beyond FLRW

Cited by 8 publications

References 22 publications

On the homogeneity of SnIa absolute magnitude in the Pantheon+ sample

On the homogeneity of SnIa absolute magnitude in the Pantheon+ sample

Nonlocal de Sitter gravity and its exact cosmological solutions

Dipole cosmology: the Copernican paradigm beyond FLRW

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