Modified cosmology through nonextensive horizon thermodynamics

TL;DR

This paper develops modified cosmological models using nonextensive thermodynamics, leading to new dark energy behaviors and compatibility with observational data, without requiring a cosmological constant.

Contribution

It introduces a novel approach applying Tsallis entropy to horizon thermodynamics, resulting in modified equations that can mimic standard cosmology and explain dark energy phenomena.

Findings

The model reproduces the universe's thermal history with matter and dark energy eras.

Dark energy equation-of-state varies with the nonextensive parameter, allowing quintessence or phantom behavior.

The scenario fits Supernovae Ia data well, even without a cosmological constant.

Abstract

We construct modified cosmological scenarios through the application of the first law of thermodynamics in the universe horizon, but using the generalized, nonextensive Tsallis entropy instead of the usual Bekenstein-Hawking one. We result to modified cosmological equations that possess the usual ones as a particular limit, but which in the general case contain extra terms that appear for the first time, that constitute an effective dark energy sector quantified by the nonextensive parameter $\delta$. When the matter sector is dust, we extract analytical expressions for the dark energy density and equation-of-state parameters, and we extend these solutions to the case where radiation is present too. We show that the universe exhibits the usual thermal history, with the sequence of matter and dark-energy eras, and according to the value of $\delta$ the dark-energy equation-of-state parameter can be quintessence-like, phantom-like, or experience the phantom-divide crossing during the evolution. Even in the case where the explicit cosmological constant is absent, the scenario at hand can very efficiently mimic $\Lambda$CDM cosmology, and is in excellent agreement with Supernovae type Ia observational data.