Thermodynamics in Modified Gravity Theories

Abstract

We demonstrate that there does exist an equilibrium description of thermodynamics on the apparent horizon in the expanding cosmological background for a wide class of modified gravity theories with the Lagrangian density $f(R,\varphi ,X)$, where $R$ is the Ricci scalar and $X$ is the kinetic energy of a scalar field $\varphi$. This comes from a suitable definition of an energy momentum tensor of the "dark" component obeying the local energy conservation law in the Jordan frame. It is shown that the equilibrium description in terms of the horizon entropy $S$ is convenient because it takes into account the contribution of the horizon entropy $\hat{S}$ in non-equilibrium thermodynamics as well as an entropy production term.

8 pages, no figure, revised version, to be published in the Proceedings of the "2nd International Workshop on Dark Matter, Dark Energy and Matter-Antimatter Asymmetry."

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• Non-equilibrium Thermodynamics of Spacetime
• Dynamic black-hole entropy
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• Wald's entropy is equal to a quarter of the horizon area in units of the effective gravitational coupling
• The generalized second law of thermodynamics in generalized gravity theories
• F(R) gravity equation of state
• Equilibrium thermodynamics in modified gravitational theories

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• Generalized Second Law of Thermodynamics in $f(T)$ Gravity with Entropy Corrections
• Quasiperiodic oscillations, weak field lensing and shadow cast around black holes in Symmergent gravity
• Thermodynamic properties of modified gravity theories
• Note on the emergence of cosmic space in modified gravities
• Thermodynamics of Gravitationally Induced Particle Creation Scenario in DGP Braneworld
• Thermodynamics of the most generalized form of Holographic Dark Energy and some particular cases with Corrected Entropies
• Thermodynamics and holography of tachyon cosmology
• Entropic force law in the presence of a noncommutative inspired spacetime for a solar system scale
• Scalar-Field Reconstruction of Ricci--Gauss--Bonnet Dark Energy in Hořava--Lifshitz Cosmology