Luminosity distance and anisotropic sky-sampling at low redshifts: A numerical relativity study

Abstract

Most cosmological data analysis today relies on the Friedmann-Lemaître-Robertson-Walker (FLRW) metric, providing the basis of the current standard cosmological model. Within this framework, interesting tensions between our increasingly precise data and theoretical predictions are coming to light. It is therefore reasonable to explore the potential for cosmological analysis outside of the exact FLRW cosmological framework. In this work we adopt the general luminosity-distance series expansion in redshift with no assumptions of homogeneity or isotropy. This framework will allow for a full model-independent analysis of near-future low-redshift cosmological surveys. We calculate the effective observational 'Hubble', 'deceleration', 'curvature' and 'jerk' parameters of the luminosity-distance series expansion in numerical relativity simulations of realistic structure formation, for observers located in different environments and with different levels of sky-coverage. With a 'fairly-sampled' sky, we find 2% and 15% cosmic variance in the 'Hubble' and 'deceleration' parameters for scales of 200 Mpc=h (corresponding to density contrasts of ∼0.1 in the simulated model universe), respectively. On top of this, we find that typical observers measure maximal sky-variance of 7% and 550% in the same parameters, as compared to their analogies in the large scale FLRW model. Our work suggests the inclusion of low-redshift anisotropy in cosmological analysis could be important for drawing correct conclusions about our Universe.

Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies

“…In Refs. [1394], the analytical expression of the luminosity distance in Eqs. ( 122)-( 124) was analysed for an ensemble of observers in fully relativistic large scale numerical simulations.…”

“…The signatures of the anisotropy of the luminosity distance cosmography as seen for the ensemble of observers, and the variations of the cosmography across observers, are discussed in Ref. [1394], in context of the Hubble tension. The dominant dipole as seen in Q and R for the observer in Fig.…”

“…Some of these assumptions are as obvious as the ΛCDM background geometry, while others are hidden in the details. The misuse of measured data based on ΛCDM assumptions on the beyond-ΛCDM models where these assumptions break down could result in misleading conclusions [547,1394,[2289][2290][2291]. To combat this, theorists should be cautious when analyzing their models, and observers should be clear about the specific assumptions in published key paper results, if possible.…”

The art of building a smooth cosmic distance ladder in a perturbed universe

“…In general, there could be corrections to the FLRW approximation [64,65]. Putting all these back into equation (72) gives a smooth distance modulus…”

Probing the Anisotropic Universe with Gravitational Waves

“…Overall, the errors are consistent with an isotropic Universe, but this exercise can be repeated as GW statistics improve. If the anisotropy is substantiated by both EM and GW events in time, it not only may explain CMB anomalies [8,9,10], but raises a host of interesting theoretical questions [75,76,77,78,79], which can be tested observationally [80,81].…”