GRAMSES: a new route to general relativistic <i>N</i>-body simulations in cosmology. Part I. Methodology and code description

Barrera-Hinojosa, Cristian; Li, Baojiu

doi:10.1088/1475-7516/2020/01/007

Cited by 39 publications

(57 citation statements)

References 97 publications

(147 reference statements)

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“…Several extensions are possibles for this work: at very large scale it could be interesting to see the impact of a fully general relativistic treatment, either by correcting the results from a Newtonian N-body code (Chisari & Zaldarriaga 2011;Fidler et al 2015) or by directly using GR simulations (Adamek et al 2016;Barrera-Hinojosa & Li 2020). At smaller scales, one could investigate the effect of strong lensing, allowing for multiple images for a single source.…”

Section: Discussionmentioning

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: Discussionmentioning

confidence: 99%

Theoretical and numerical perspectives on cosmic distance averages

Breton

Fleury

2021

A&A

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“…The only danger through naming is to neglect correlations and covariances between different measurements 19. For cosmological N-body simulations, the readers might be interested to references[152][153][154].…”

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confidence: 99%

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

Valentino

Mena²,

Pan³

et al. 2021

Class. Quantum Grav.

1,311

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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“…We also point to the quite recent advent of numerical tools that allow to simulate increasingly realistic models of the Universe, including relativistic effects (Löffler et al, 2012;Mertens et al, 2016) and N-body simulations (Adamek et al, 2016;Barrera-Hinojosa and Li, 2020). Using the N-body relativistic code "gevolution," Adamek et al (2019) find that backreaction on the expansion rate in a ΛCDM and an Einstein-de Sitter Universe remains small if one chooses averaging volumes related to the Poisson gauge, while when choosing comoving gauge backreaction is of the order of 15%.…”

Section: Classical Backreactionmentioning

confidence: 96%

Backreaction in Cosmology

Schander

Thiemann²

2021

Front. Astron. Space Sci.

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In this review, we investigate the question of backreaction in different approaches to cosmological perturbation theory, and with a special focus on quantum theoretical aspects. By backreaction we refer here to the effects of matter field or cosmological inhomogeneities on the homogeneous dynamical background degrees of freedom of cosmology. We begin with an overview of classical cosmological backreaction which is ideally suited for physical situations in the late time Universe. We then proceed backwards in time, considering semiclassical approaches such as semiclassical or stochastic (semiclassical) gravity which take quantum effects of the perturbations into account. Finally, we review approaches to backreaction in quantum cosmology that should apply to the very early Universe where classical and semiclassical approximations break down. The main focus is on a recently proposed implementation of backreaction in quantum cosmology using a Born–Oppenheimer inspired method.

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GRAMSES: a new route to general relativistic N-body simulations in cosmology. Part I. Methodology and code description

Cited by 39 publications

References 97 publications

Theoretical and numerical perspectives on cosmic distance averages

Theoretical and numerical perspectives on cosmic distance averages

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

Backreaction in Cosmology

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GRAMSES: a new route to general relativistic N-body simulations in cosmology. Part I. Methodology and code description

Cited by 39 publications

References 97 publications

Theoretical and numerical perspectives on cosmic distance averages

Theoretical and numerical perspectives on cosmic distance averages

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

Backreaction in Cosmology

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Product

Resources

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