CMB acoustic scale in the entropic-like accelerating universe

TL;DR

This paper explores a generalized entropic accelerating universe model, deriving its background equations, calculating the CMB acoustic scale, and establishing bounds on model parameters, with potential for future observational distinction from standard Lambda-CDM.

Contribution

It introduces a generalized entropic universe model with a new parameter, derives its background equations, and assesses its observational signatures through the CMB acoustic scale.

Findings

The model's parameter gamma is tightly constrained by the acoustic scale.

Future data could differentiate this model from standard Lambda-CDM.

The background equations can be mapped to a dark energy model with a specific equation of state.

Abstract

We consider generalizations of the entropic accelerating universe recently proposed in Ref. [4,5] and show that their background equations can be made equivalent to a model with a dark energy component with constant parameter of state $w_{X} = -1 + 2\, \gamma /3$, where $\gamma$ is related to the coefficients of the new terms in the Friedman equations. After discussing all the Friedman equations for an arbitrary $\gamma$, we show how to recover the standard scalings for dust and radiation. The acoustic scale $\ell_A$, related to the peak positions in the pattern of the angular power spectrum of the Cosmic Microwave Background anisotropies, is also computed and yields the stringent bound $|\gamma|\ll 1$. We then argue that future data might be able to distinguish this model from pure $\Lambda$CDM (corresponding to $\gamma=0$).