Back reaction from walls

Vonlanthen, Marc; Durrer, Ruth

doi:10.1088/1475-7516/2012/02/036

Cited by 16 publications

(21 citation statements)

References 45 publications

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“…However, the proof presented in [97] assumes that the angular element is given by the FRW metric, which is the question to be investigated [98], and the LTB model has been used to provide an exact counterexample [99] (see also [100]). It has also been argued that the distance is close to FRW as long as light travels through compensated over-and underdensities, and the time spent by a light ray in a given region is much smaller than the timescale for the evolution of the gravitational potential of the region [42]. (This argument is tied to perturbation theory, as the gravitational potential is a perturbative concept.)…”

Section: Signatures Of Backreactionmentioning

confidence: 99%

Average expansion rate and light propagation in a cosmological Tardis spacetime

Lavinto

Räsänen

Szybka

2013

J. Cosmol. Astropart. Phys.

112

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Abstract. We construct the first exact statistically homogeneous and isotropic cosmological solution in which inhomogeneity has a significant effect on the expansion rate. The universe is modelled as a Swiss Cheese, with dust FRW background and inhomogeneous holes. We show that if the holes are described by the quasispherical Szekeres solution, their average expansion rate is close to the background under certain rather general conditions. We specialise to spherically symmetric holes and violate one of these conditions. As a result, the average expansion rate at late times grows relative to the background, i.e. backreaction is significant. The holes fit smoothly into the background, but are larger on the inside than a corresponding background domain: we call them Tardis regions. We study light propagation, find the effective equations of state and consider the relation of the spatially averaged expansion rate to the redshift and the angular diameter distance.

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Section: Signatures Of Backreactionmentioning

confidence: 99%

Average expansion rate and light propagation in a cosmological Tardis spacetime

Lavinto

Räsänen

Szybka

2013

J. Cosmol. Astropart. Phys.

112

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“…In Ref. [8] we had to choose the initial overdensities such that no singularity was encountered up to the present time. In these Universes, the directions normal to the collapse, i.e.…”

Section: Relativistic and Semi-relativistic Wall Universesmentioning

confidence: 99%

Distance-redshift relation in plane symmetric universes

2014

Self Cite

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Distance measurements are usually thought to probe the 'background' metric of the universe, but in reality the presence of perturbations will lead to deviations from the result expected in an exactly homogeneous and isotropic universe. At least in principle the presence of perturbations could even explain the observed distance-redshift relation without the need for dark energy. In this paper we re-investigate a toy model where perturbations are plane symmetric, and for which exact solutions are known in the fluid limit. However, if perturbations are large, shell-crossing occurs and the fluid approximation breaks down. This prevents the study of the most interesting cases. Here we use a general-relativistic N -body simulation that does not suffer from this problem and which allows us to go beyond previous works. We show that even for very large plane-symmetric perturbations we are not able to mimic the observed distance-redshift relation. We also discuss how the synchronous comoving gauge breaks down when shell-crossing occurs, while metric perturbations in the longitudinal gauge remain small. For this reason the longitudinal (Newtonian) gauge appears superior for relativistic N -body simulations of large-scale structure formation.PACS numbers: 98.80.Es, 98.80.Jk, 98.65.Dx

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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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Back reaction from walls

Cited by 16 publications

References 45 publications

Average expansion rate and light propagation in a cosmological Tardis spacetime

Average expansion rate and light propagation in a cosmological Tardis spacetime

Distance-redshift relation in plane symmetric universes

Theoretical and numerical perspectives on cosmic distance averages

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