CMB acoustic scale in the entropic-like accelerating universe

Understand

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 $|\gamma|\ll 1$.