Cosmological scenario based on the first and second laws of thermodynamics: Thermodynamic constraints on a generalized cosmological model
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866910984977776640 |
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| author | Komatsu, Nobuyoshi |
| author_facet | Komatsu, Nobuyoshi |
| contents | 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 $S_{H}$ on a cosmological horizon. Then, the cosmological equations were formulated based on a general formulation that includes two extra driving terms, $f_Λ(t)$ and $h_{\textrm{B}}(t)$, which are usually used for, e.g., time-varying $Λ(t)$ 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 [Phys. Rev. D 99, 043523 (2019) (arXiv:1810.11138)]. It is found that a deviation $S_Δ$ of $S_{H}$ from the Bekenstein-Hawking entropy plays important roles in the two terms. The second law should constrain the upper limits of $f_Λ(t)$ and $h_{\textrm{B}}(t)$ in our late Universe. The orders of the two terms are likely consistent with the order of the cosmological constant $Λ_{\textrm{obs}}$ measured by observations. In particular, when the deviation $S_Δ$ is close to zero, $h_{\textrm{B}}(t)$ and $f_Λ(t)$ should reduce to zero and a constant value (consistent with the order of $Λ_{\textrm{obs}}$), respectively, as if a consistent and viable scenario could be obtained from thermodynamics. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2412_19032 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Cosmological scenario based on the first and second laws of thermodynamics: Thermodynamic constraints on a generalized cosmological model Komatsu, Nobuyoshi General Relativity and Quantum Cosmology Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology 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 $S_{H}$ on a cosmological horizon. Then, the cosmological equations were formulated based on a general formulation that includes two extra driving terms, $f_Λ(t)$ and $h_{\textrm{B}}(t)$, which are usually used for, e.g., time-varying $Λ(t)$ 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 [Phys. Rev. D 99, 043523 (2019) (arXiv:1810.11138)]. It is found that a deviation $S_Δ$ of $S_{H}$ from the Bekenstein-Hawking entropy plays important roles in the two terms. The second law should constrain the upper limits of $f_Λ(t)$ and $h_{\textrm{B}}(t)$ in our late Universe. The orders of the two terms are likely consistent with the order of the cosmological constant $Λ_{\textrm{obs}}$ measured by observations. In particular, when the deviation $S_Δ$ is close to zero, $h_{\textrm{B}}(t)$ and $f_Λ(t)$ should reduce to zero and a constant value (consistent with the order of $Λ_{\textrm{obs}}$), respectively, as if a consistent and viable scenario could be obtained from thermodynamics. |
| title | Cosmological scenario based on the first and second laws of thermodynamics: Thermodynamic constraints on a generalized cosmological model |
| topic | General Relativity and Quantum Cosmology Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2412.19032 |