Observational constraints of the modified cosmology through Barrow entropy

TL;DR

This paper explores how Barrow entropy modifies cosmological equations and uses observational data to constrain these modifications, showing potential improvements in resolving Hubble and sigma_8 tensions.

Contribution

It derives modified Friedmann equations from Barrow entropy and constrains the resulting cosmology using multiple observational datasets.

Findings

Higher H_0 values with phantom dark energy in Barrow cosmology.

Slight reduction in H_0 tension with Planck + Pantheon + BAO dataset.

Amelioration of sigma_8 tension with additional datasets.

Abstract

Taking into account a fractal structure for the black hole horizon, Barrow argued that the area law of entropy is modified due to quantum-gravitational effects (Barrow in Phys Lett B 808:135643, https://doi.org/10.1016/j.physletb.2020.135643, 2020). Accordingly, the corrected entropy takes the form $S \sim A^{1+\mathrm{\Delta}/2}$, where $0\leq\mathrm{\Delta}\leq1$, indicates the amount of the quantum-gravitational deformation effects. In this paper, based on Barrow entropy, we first derive the modified gravitational field equations through the Clausius relation. We then consider the Friedmann-Lema\^itre-Robertson-Walker (FLRW) metric as the background metric and derive the modified Friedmann equations inspired by Barrow entropy. In order to explore observational constraints on the modified Barrow cosmology, we employ two different combinations of available datasets, mainly "Planck + Pantheon + BAO" and "Planck + Planck-SZ + CFHTLenS + Pantheon + BAO + BAORSD" datasets,. According to numerical results, we observe that the "Planck + Pantheon + BAO" dataset predicts higher values of $H_0$ in Barrow cosmology with a phantom dark energy compared to $\mathrm{\Lambda}$CDM, so tensions between low redshift determinations of the Hubble constant and cosmic microwave background (CMB) results are slightly reduced. On the other hand, in case of dataset "Planck + Planck-SZ + CFHTLenS + Pantheon + BAO + BAORSD" there is a slight amelioration in $\sigma_8$ tension in Barrow cosmology with a quintessential dark energy compared to the standard model of cosmology. Additionally, for a more reliable comparison, we also constrain the wCDM model with the same datasets, where our results exhibit a satisfying compatibility between Barrow cosmology and wCDM.