New Framework for Apparent Horizon Entropy in Modified Gravity Models
Researchers have developed a revised formalism for apparent horizon entropy in modified gravity theories to test the validity of the Generalized Second Law (GSL) of thermodynamics in a Friedmann-Robertson-Walker universe. The new entropy relation extends the standard Bekenstein-Hawking term with an additional integral contribution capturing energy density and pressure deviations from general relativity. The work suggests that this revised entropy can improve late-time GSL validity for certain f(T) and f(R) gravity models, strengthening the theoretical link between thermodynamics and gravity.
A study published in the European Physical Journal C presents a universal, revisited formalism for the entropy of the apparent horizon in modified gravity, aimed at rigorously testing the Generalized Second Law (GSL) of thermodynamics. The entropy relation is derived directly from modified Friedmann equations in a Friedmann-Robertson-Walker universe and extends the classical Bekenstein-Hawking entropy by incorporating an additional integral term that encodes effective energy density and pressure arising from deviations from general relativity. Using this generalized entropy formula, the authors derive a compact expression for the GSL and apply it to several viable f(T) and f(R) gravity models, evaluating GSL validity as a function of cosmological redshift. The analysis finds that including the integral correction term relatively improves late-time GSL compliance for some models while leaving others unchanged. The results reinforce the deep connection between gravitational dynamics and thermodynamic principles in cosmological settings. The paper spans 23 pages, includes 2 figures and 2 tables, and was submitted to arXiv in December 2025 with a revised version posted in June 2026.
What's missing
The study does not explicitly address how sensitive the GSL validity conclusions are to the choice of specific model parameters within the f(T) and f(R) frameworks, nor does it discuss whether the revised formalism has been tested against observational cosmological data. The generality of the 'universal' entropy formula across all modified gravity theories beyond f(T) and f(R) remains an open question.
What different sources said
- arXiv astro-phCenter
Revisited apparent horizon entropy and GSL in modified gravity
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