Calculation of distances in cosmological models with small-scale inhomogeneities and their use in observational cosmology: a review

Helbig, Phillip

doi:10.21105/astro.1912.12269

Cited by 7 publications

(5 citation statements)

References 223 publications

(321 reference statements)

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“…The fundamental question of whether the average D(z) is the same as the D(z) of the average Universe goes back more than 50 years, when Zel'dovich (1964) and Feynman (in a colloquium given at Caltech the same year) 1 suggested the following: if the Universe is lumpy, then a typical light beam should mostly propagate through under-dense regions, and thereby be de-focussed with respect to FLRW; this should imply that D(z) is actually biased up. Many developments and counter-arguments followed from that seminal idea; we refer the interested reader to the introduction of Kaiser & Peacock (2016, hereafter KP16) and the comprehensive review by Helbig (2020) for details.…”

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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Section: Introductionmentioning

confidence: 99%

Theoretical and numerical perspectives on cosmic distance averages

Breton

Fleury

2021

A&A

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“…One constraint that any acceptable model should satisfy is that the variations in extinction, across different lines of sight at the same redshift, must be small, because of the small photometric scatter around the mean that is observed for type Ia SNe. This requirement parallels the situation with gravitational lensing of type Ia SNe: the small observed dispersion in fluxes places an upper limit on the mass of the elementary lumps of matter, such that the luminosity distance is well approximated by that of a homogeneous universe (Metcalf & Silk 1999;Zumalacárregui & Seljak 2018;Helbig 2020). The latter condition is satisfied if we expect to have a number 𝑁 1 elementary lumps of matter within the "beam" -i.e.…”

Section: Extinction Fluctuationsmentioning

confidence: 81%

Cosmological nanolensing by dense gas clouds

Tuntsov,

Walker

2022

Preprint

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We study the influence of a cosmological population of dense gas clouds on distant sources, with emphasis on quasar optical variability. In addition to gravitational lensing such clouds affect flux measurements via refraction in the neutral gas and via dust extinction, leading to a variety of possible light curves even in the low optical depth limit. We classify and illustrate the types of light curves that can arise. For sources as large as quasars we show that gravitational lensing and extinction are the dominant effects, with gas refraction playing only a minor rôle. We find that clouds with mass ∼ 10 −4.5±0.5 M can reproduce the observed distribution of quasar variation amplitudes, but only if such clouds make up a large fraction of the closure density. In that case there may also be substantial extinction of distant optical sources, which can in principle be constrained by data on "standard candles" such as type Ia supernovae. Unfortunately that extinction is essentially grey, even when the material opacity is strongly wavelength dependent, making it difficult to distinguish from the influence of the background geometry. We propose a novel statistical test of the origin of quasar variability, based on the angular structure of the variation timescale for a large number of quasars distributed all over the sky. If quasar variability is primarily due to nanolensing that angular structure is expected to include a quadrupole term of amplitude ∼ 5%, which ought to be measurable with future data from the Gaia mission.

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“…As a future work, a more thorough analysis is needed using inhomogeneous cosmological metrics. Several interesting works evaluate the luminosity distance in inhomogeneous cosmological models [62]. However, in all these works that include a CC, this CC takes the same value in the different parts of the Universe.…”

Section: Discussionmentioning

confidence: 99%

Phenomenological footprints of Λ varying gravity theories inspired from quantum gravity models in the multi-messenger era

Good,

Zarikas

2023

Class. Quantum Grav.

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An interesting phenomenological consequence of $\Lambda$ varying gravity theories inspired by quantum gravity models is reported. The treatment in the present work is quite general and applicable to several different actions with $\Lambda$ varying, especially those used in RG approaches to quantum gravity. An effective gravitational action with a scale varying cosmological constant, $\Lambda$, which depends on the system's characteristics, like the length and the energy density, is the key feature. If the system is an astrophysical object, like a cluster of galaxies, a black hole, etc, non-negligible corrections arise to several observable quantities.Distinctive footprints could refer to luminosity distance and strong/weak lensing measurements, among others. The present study focuses on the SNIa luminosity distance observable.

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Calculation of distances in cosmological models with small-scale inhomogeneities and their use in observational cosmology: a review

Cited by 7 publications

References 223 publications

Theoretical and numerical perspectives on cosmic distance averages

Theoretical and numerical perspectives on cosmic distance averages

Cosmological nanolensing by dense gas clouds

Phenomenological footprints of Λ varying gravity theories inspired from quantum gravity models in the multi-messenger era

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