Cosmological scenario based on the first and second laws of thermodynamics: thermodynamic constraints on a generalized cosmological model
Abstract The first and second laws of thermodynamics should lead to a consistent scenario for discussing the cosmological constant problem. In the present study, to establish such a thermodynamic scenario, cosmological equations in a flat Friedmann–Lemaître–Robertson–Walker universe were derived fro...
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| Format: | Article |
| Language: | English |
| Published: |
SpringerOpen
2025-06-01
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| Series: | European Physical Journal C: Particles and Fields |
| Online Access: | https://doi.org/10.1140/epjc/s10052-025-14332-5 |
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| Summary: | Abstract The first and second laws of thermodynamics should lead to a consistent scenario for discussing the cosmological constant problem. In the present study, to establish such a thermodynamic scenario, cosmological equations in a flat Friedmann–Lemaître–Robertson–Walker universe were derived from the first law, using an arbitrary entropy $$S_{H}$$ S H on a cosmological horizon. Then, the cosmological equations were formulated based on a general formulation that includes two extra driving terms, $$f_{\Lambda }(t)$$ f Λ ( t ) and $$h_{\text {B}}(t)$$ h B ( t ) , which are usually used for, e.g., time-varying $$\Lambda (t)$$ Λ ( t ) cosmology and bulk viscous cosmology, respectively. In addition, thermodynamic constraints on the two terms are examined using the second law of thermodynamics, extending a previous analysis (Komatsu in Phys. Rev. D 99:043523, 2019). It is found that a deviation $$S_{\Delta }$$ S Δ of $$S_{H}$$ S H from the Bekenstein–Hawking entropy plays important roles in the two terms. The second law should constrain the upper limits of $$f_{\Lambda }(t)$$ f Λ ( t ) and $$h_{\text {B}}(t)$$ h B ( t ) in our late Universe. The orders of the two terms are likely consistent with the order of the cosmological constant $$\Lambda _{\text {obs}}$$ Λ obs measured by observations. In particular, when the deviation $$S_{\Delta }$$ S Δ is close to zero, $$h_{\text {B}}(t)$$ h B ( t ) and $$f_{\Lambda }(t)$$ f Λ ( t ) should reduce to zero and a constant value (consistent with the order of $$\Lambda _{\text {obs}}$$ Λ obs ), respectively, as if a consistent and viable scenario could be obtained from thermodynamics. |
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| ISSN: | 1434-6052 |