$\Lambda$CDM without cosmological constant

TL;DR

This paper proposes a modified gravity model that mimics $ ext{Lambda}$CDM at large scales but differs in recent cosmic evolution, potentially resolving current observational tensions.

Contribution

It introduces an exponential correction to General Relativity that behaves like a cosmological constant at high curvature but vanishes in flat space, with testable differences from $ ext{Lambda}$CDM.

Findings

Model aligns with current cosmological observations.

Predicts measurable deviations from $ ext{Lambda}$CDM in recent cosmic evolution.

Offers potential explanations for $f\sigma_8$ tension.

Abstract

A type of exponential correction to General Relativity gives viable modified gravity model of dark energy. The model behaves as $R-2\Lambda$ at large curvature where an effective cosmological constant appears, but it becomes zero in flat space time. The cosmic evolution of the main density parameters is consistent with current observations. The thin shell conditions for the Solar system were analyzed. Apart from satisfying cosmological and local gravity restrictions, the model may also show measurable differences with $\Lambda$CDM at recent times. The current value of the deviation parameter $m$ for scales relevant to the matter power spectrum can be larger than $10^{-6}$. The growth index of matter density perturbations is clearly different from that of the $\Lambda$CDM. The theoretical predictions of the model for the weighted growth rate were analyzed in the light of the $f\sigma_8$-tension.