Scalar-tensor gravity admits a frame-invariant perfect-fluid description with zero temperature, so that general relativity corresponds to diffusive equilibrium for both minimal and nonminimal theories.
Non-equilibrium Thermodynamics of Spacetime
9 Pith papers cite this work. Polarity classification is still indexing.
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abstract
It has previously been shown that the Einstein equation can be derived from the requirement that the Clausius relation dS = dQ/T hold for all local acceleration horizons through each spacetime point, where dS is one quarter the horizon area change in Planck units, and dQ and T are the energy flux across the horizon and Unruh temperature seen by an accelerating observer just inside the horizon. Here we show that a curvature correction to the entropy that is polynomial in the Ricci scalar requires a non-equilibrium treatment. The corresponding field equation is derived from the entropy balance relation dS =dQ/T+dS_i, where dS_i is a bulk viscosity entropy production term that we determine by imposing energy-momentum conservation. Entropy production can also be included in pure Einstein theory by allowing for shear viscosity of the horizon.
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First background-level constraints on Luciano-Saridakis entropic cosmology using CC, Pantheon+ with SH0ES, DESI DR2 BAO and compressed Planck data show robust fit, 2sigma exclusion of LambdaCDM, and potential Hubble tension alleviation.
Entropy production in a stochastic spacetime metric flow vanishes exactly on solutions of the Einstein equations, making classical GR the reversible limit of an underlying stochastic geometro-dynamics.
Affine group symmetries on the light ray, with dilations implementing modular flow, provide the minimal structure for thermality on the Rindler horizon via the Mellin transform bridge between Minkowski and Rindler modes.
Authors add f(R, K) to the Einstein-Hilbert action, obtain higher-derivative-free modified Friedmann equations for flat FRW, and derive a general apparent-horizon entropy expression usable for multiple entropy models.
Applying Jacobson's thermodynamic derivation to general non-Riemannian spacetimes selects a unique Einstein-Hilbert-plus-torsion-vector-squared theory in the torsion-only case, and yields no action-based theory when non-metricity is present.
Hamilton-Jacobi analysis of slow-roll inflation with non-Bekenstein-Hawking entropies yields fitted entropy parameters (δ≈1.1-1.2, α∼10^{-14}, K∼10^{-17}) consistent with ns and r data.
A two-parameter extension of Bekenstein entropy is applied to derive the Friedmann equations and confirm thermodynamic consistency for an accelerating universe via entropy balance and maximization.
Entropy production terms in non-equilibrium horizon thermodynamics of modified gravity have distinct origins and roles depending on whether Rindler or apparent horizons are used.
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First background-level constraints on Luciano-Saridakis entropic cosmology using CC, Pantheon+ with SH0ES, DESI DR2 BAO and compressed Planck data show robust fit, 2sigma exclusion of LambdaCDM, and potential Hubble tension alleviation.
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Entropy Production and the Gravitational Origin of the Second Law
Entropy production in a stochastic spacetime metric flow vanishes exactly on solutions of the Einstein equations, making classical GR the reversible limit of an underlying stochastic geometro-dynamics.
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Affine group symmetries on the light ray, with dilations implementing modular flow, provide the minimal structure for thermality on the Rindler horizon via the Mellin transform bridge between Minkowski and Rindler modes.
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Modified Entropy from Action Principle
Authors add f(R, K) to the Einstein-Hilbert action, obtain higher-derivative-free modified Friedmann equations for flat FRW, and derive a general apparent-horizon entropy expression usable for multiple entropy models.
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Jacobson's thermodynamic approach to classical gravity applied to non-Riemannian geometries: remarks on the simplicity of Nature
Applying Jacobson's thermodynamic derivation to general non-Riemannian spacetimes selects a unique Einstein-Hilbert-plus-torsion-vector-squared theory in the torsion-only case, and yields no action-based theory when non-metricity is present.
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Hamilton-Jacobi Approach to Inflationary Scenarios through Extended Entropies: An Observational Perspective
Hamilton-Jacobi analysis of slow-roll inflation with non-Bekenstein-Hawking entropies yields fitted entropy parameters (δ≈1.1-1.2, α∼10^{-14}, K∼10^{-17}) consistent with ns and r data.
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Generalized Mass-to-Horizon Entropy and Horizon Thermodynamics
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Entropy production terms in non-equilibrium horizon thermodynamics of modified gravity have distinct origins and roles depending on whether Rindler or apparent horizons are used.