Towards statistically homogeneous and isotropic perfect fluid universes with cosmic backreaction

Koksbang, S. M.

doi:10.1088/1361-6382/ab376c

Cited by 20 publications

(16 citation statements)

References 104 publications

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“…This cancellation has also been shown to occur for perturbed FLRW models [55]. The cancellation was, however, not found to occur in the recently presented (somewhat exotic) LTB Swiss cheese model in [56].…”

Section: The Redshift Is Defined Bymentioning

confidence: 61%

Light path averages in spacetimes with nonvanishing average spatial curvature

Koksbang

2019

Phys. Rev. D

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Effects of inhomogeneities on observations have been vastly studied using both perturbative methods, N-body simulations and Swiss cheese solutions to the Einstein equations. In nearly all cases, such studied setups assume vanishing spatial background curvature. While a spatially flat Friedmann-Lemaitre-Robertson-Walker model is in accordance with observations, a non-vanishing curvature is not ruled out. It is therefore important to note that, as has been pointed out in the literature, 1 dimensional averages might not converge to volume averages in non-Euclidean space. If this is indeed the case, it will affect the interpretation of observations in spacetimes with non-vanishing average spatial curvature. This possibility is therefore studied here by computing the integrated expansion rate and shear, the accumulated density contrast, and fluctuations in the redshift-distance relation in Swiss cheese models with different background curvatures. It is found that differences in mean and dispersion of these quantities in the different models are small and naturally attributable to differences in background expansion rate and density contrasts. Thus, the study does not yield an indication that the relationship between 1 dimensional spatial averages and volume averages depends significantly on background curvature. arXiv:1909.00610v2 [astro-ph.CO]

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Section: The Redshift Is Defined Bymentioning

confidence: 61%

Light path averages in spacetimes with nonvanishing average spatial curvature

Koksbang

2019

Phys. Rev. D

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“…As a first step, a significant research endeavour was dedicated to ray tracing and distance measurements in cosmological toy-models, such as Swiss-cheese models (Brouzakis et al 2007(Brouzakis et al , 2008Marra et al 2008;Biswas & Notari 2008;Vanderveld et al 2008;Valkenburg 2009;Clifton & Zuntz 2009;Bolejko 2009Bolejko , 2011Bolejko & Célérier 2010;Szybka 2011;Flanagan et al 2013;Fleury et al 2013;Fleury 2014;Troxel et al 2014;Peel et al 2014;Lavinto & Rasanen 2015;Koksbang 2017Koksbang , 2019aKoksbang ,b, 2020a, plane-parallel Universes (Di Dio et al 2012), or lattice models (Clifton & Ferreira 2009a,b, 2011Clifton et al 2012;Liu 2015;Bruneton & Larena 2013;Bentivegna et al 2017;Sanghai et al 2017;Koksbang 2020b). These works generally agreed with the relevant theoretical predictions.…”

Section: Introductionmentioning

confidence: 99%

Theoretical and numerical perspectives on cosmic distance averages

Breton

Fleury

2021

A&A

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The interpretation of cosmological observations relies on a notion of an average Universe, which is usually considered as the homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker (FLRW) model. However, inhomogeneities may statistically bias the observational averages with respect to FLRW, notably for distance measurements, due to a number of effects such as gravitational lensing and redshift perturbations. In this article, we review the main known theoretical results on average distance measures in cosmology, based on second-order perturbation theory, and we fill in some of their gaps. We then comprehensively test these theoretical predictions against ray tracing in a high-resolution dark-matter N-body simulation. This method allows us to describe the effect of small-scale inhomogeneities deep into the non-linear regime of structure formation on light propagation up to z = 10. We find that numerical results are in remarkably good agreement with theoretical predictions in the limit of super-sample variance. No unexpectedly large bias originates from very small scales, whose effect is fully encoded in the non-linear power spectrum. Specifically, the directional average of the inverse amplification and the source-averaged amplification are compatible with unity; the change in area of surfaces of constant cosmic time is compatible with zero; the biases on other distance measures, which can reach slightly less than 1% at high redshift, are well understood. As a side product, we also confront the predictions of the recent finite-beam formalism with numerical data and find excellent agreement.

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“…The effective redshift is defined in terms of the averaged scalefactor aD of the domain D. The covariant scheme can be applied provided that the spatial averages are calculated on the hypersurfaces of statistical homogeneity and isotropy, and the evolution of structure in the Universe is sufficiently slow in the time-interval of propagation of the wave from source to observer. It has been shown [35,45] that for a model like ours, the covariant scheme is suitable for describing the relation between the effective redshift and cosmological angular diameter-distance.…”

Section: Modification Of Redshift and Distance Calculation In The Bac...mentioning

confidence: 76%

Effect of inhomogeneities on the propagation of gravitational waves from binaries of compact objects

Pandey,

Sarkar,

Ali

et al. 2022

Preprint

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We consider the propagation of gravitational waves in our late time Universe with the presence of structure. Gravitational waves emitted from distant sources have to traverse through regions that are far from smooth and homogeneous, before detection. We investigate the effect of inhomogeneities on the observables associated with the gravitational waves sources. In particular, we evaluate the impact of inhomogeneities on gravitational wave propagation employing the Buchert's framework of averaging. In context of a toy model within the above framework, it is first shown how the redshift versus distance relation gets affected through the averaging process. We then study the variation of the redshift dependent part of the observed gravitational wave amplitude for different combination of our model parameters. We show that the variation of the gravitational wave amplitude with respect to redshift can deviate significantly in comparison with that in the ΛCDM-model. Our result signifies the importance of local inhomogeneities on precision measurements of parameters of gravitational wave sources.

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Towards statistically homogeneous and isotropic perfect fluid universes with cosmic backreaction

Cited by 20 publications

References 104 publications

Light path averages in spacetimes with nonvanishing average spatial curvature

Light path averages in spacetimes with nonvanishing average spatial curvature

Theoretical and numerical perspectives on cosmic distance averages

Effect of inhomogeneities on the propagation of gravitational waves from binaries of compact objects

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