RESEARCH
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Second law of thermodynamics in nonminimally coupled gravity

R. P. L. Azevedo, P. P. Avelino

Abstract
In the present work we show that the second law of thermodynamics does not generally hold if the matter and gravitational fields are nonminimally coupled. We demonstrate this result by explicitly computing the evolution of the entropy of the matter fields in the case of a closed homogeneous and isotropic universe filled with dust and radiation, showing that, in this case, the sign of the entropy variation is determined by the evolution of the universe. The preservation of the second law of thermodynamics in these modified theories would require its generalization to account for a gravitational entropy contribution.

Keywords
General Relativity and Quantum Cosmology; Astrophysics - Cosmology and Nongalactic Astrophysics

Europhysics Letters
Volume 132, Number 3
2020 December

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia