Entropic cosmology for a generalized black-hole entropy

TL;DR

This paper explores entropic cosmology using generalized black-hole entropy, deriving new entropic-force terms that can explain both accelerating and decelerating universe behaviors, aligning with supernova observations.

Contribution

It introduces entropic-force models based on generalized entropy, extending previous models and connecting entropic cosmology with bulk viscous cosmology concepts.

Findings

Generalized entropy leads to an entropic-force term acting as an extra driving force.

Models fit supernova data well, matching observed cosmic acceleration.

Generalized entropy model predicts both deceleration and acceleration phases, similar to ΛCDM.

Abstract

An entropic-force scenario, i.e., entropic cosmology, assumes that the horizon of the universe has an entropy and a temperature. In the present study, in order to examine entropic cosmology, we derive entropic-force terms not only from the Bekenstein entropy but also from a generalized black-hole entropy proposed by C. Tsallis and L.J.L. Cirto [Eur. Phys. J. C \textbf{73}, 2487 (2013)]. Unlike the Bekenstein entropy, which is proportional to area, the generalized entropy is proportional to volume because of appropriate nonadditive generalizations. The entropic-force term derived from the generalized entropy is found to behave as if it were an extra driving term for bulk viscous cosmology, in which a bulk viscosity of cosmological fluids is assumed. Using an effective description similar to bulk viscous cosmology, we formulate the modified Friedmann, acceleration, and continuity equations for entropic cosmology. Based on this formulation, we propose two entropic-force models derived from the Bekenstein and generalized entropies. In order to examine the properties of the two models, we consider a homogeneous, isotropic, and spatially flat universe, focusing on a single-fluid-dominated universe. The two entropic-force models agree well with the observed supernova data. Interestingly, the entropic-force model derived from the generalized entropy predicts a decelerating and accelerating universe, as for a fine-tuned standard $\Lambda$CDM (lambda cold dark matter) model, whereas the entropic-force model derived from the Bekenstein entropy predicts a uniformly accelerating universe.