Modified cosmology through spacetime thermodynamics and Barrow horizon entropy

Abstract

We present modified cosmological scenarios that arise from the application of the "gravity-thermodynamics" conjecture, using the Barrow entropy instead of the usual Bekenstein-Hawking one. The former is a modification of the black hole entropy due to quantum-gravitational effects that deform the black-hole horizon by giving it an intricate, fractal structure. We extract modified cosmological equations which contain new extra terms that constitute an effective dark-energy sector, and which coincide with the usual Friedmann equations in the case where the new Barrow exponent acquires its Bekenstein-Hawking value. We present analytical expressions for the evolution of the effective dark energy density parameter, and we show that the universe undergoes through the usual matter and dark-energy epochs. Additionally, the dark-energy equation-of-state parameter is affected by the value of the Barrow deformation exponent and it can lie in the quintessence or phantom regime, or experience the phantom-divide crossing. Finally, at asymptotically large times the universe always results in the de-Sitter solution.

12 pages, 3 figures

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• Modified Friedmann equations from fractional entropy
• Barrow entropic Quintessence and Dilation dark energy Models with Generalized HDE cut-off
• Look beyond additivity and extensivity of entropy for black hole and cosmological horizons
• Anisotropic Conformal Dark Gravity on the Lorentz Tangent Bundle Spacetime
• Exponential correction to Friedmann equations