Kruglov-entropy cosmology from apparent-horizon thermodynamics: background dynamics and observational constraints
Abstract
We investigate two late-time cosmological models generated by Kruglov's nonadditive entropy at the apparent horizon. Model I, originally derived by Kruglov, follows the Cai--Kim thermodynamic construction and leads to an implicit modified Friedmann equation, whereas Model II, proposed and derived in this work, is obtained from an entropy-integral prescription and contains an effective vacuum contribution. We formulate both models in terms of the dimensionless Hubble parameter, include radiation, impose exact present-day closure, and evolve the physical branch using analytic derivatives of the implicit Friedmann equations. We constrain the models with DESI DR2 baryon acoustic oscillations and a compressed CMB likelihood, with and without DES-Y5 Type-Ia supernovae. Model I is driven to a markedly lower Hubble constant, H0≃62.4,km,s−1,Mpc−1 for the combined data, and remains non-phantom with wDE,0≃−0.814; it is strongly disfavoured relative to flat ΛCDM. Model II stays close to ΛCDM in the standard cosmological parameters and gives wDE,0≃−1.003, while its two entropy-sector parameters remain strongly degenerate. Its best-fit likelihood is comparable to ΛCDM, but the additional parameters are not supported by information criteria. These results show that the two thermodynamic realizations of the same nonadditive entropy have sharply different phenomenological consequences at the homogeneous-background level. In summary, the observational plausibility of entropy-based cosmology hinges critically on how the generalized horizon entropy is incorporated into the Friedmann dynamics.
Related
- Theoretical consistency and observational constraints on entropic cosmology
- Gravitational Wave Propagation in K-essence Cosmology: Theory and Observational Constraints
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BibTeX
@misc{muhammad2026krugloventropy,
title = {{Kruglov-entropy cosmology from apparent-horizon thermodynamics: background dynamics and observational constraints}},
author = {Candrasyah Muhammad and Burin Gumjudpai and Nandan Roy and Pornrad Srisawad},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.31426},
eprint = {2609.31426},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.31426},
note = {CC0},
}
RIS
TY - UNPB
TI - Kruglov-entropy cosmology from apparent-horizon thermodynamics: background dynamics and observational constraints
AU - Candrasyah Muhammad
AU - Burin Gumjudpai
AU - Nandan Roy
AU - Pornrad Srisawad
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2609.31426
UR - https://arxiv.org/abs/2609.31426
AB - We investigate two late-time cosmological models generated by Kruglov's nonadditive entropy at the apparent horizon. Model I, originally derived by Kruglov, follows the Cai--Kim thermodynamic construction and leads to an implicit modified Friedmann equation, whereas Model II, proposed and derived in this work, is obtained from an entropy-integral prescription and contains an effective vacuum contribution. We formulate both models in terms of the dimensionless Hubble parameter, include radiation, impose exact present-day closure, and evolve the physical branch using analytic derivatives of the implicit Friedmann equations. We constrain the models with DESI DR2 baryon acoustic oscillations and a compressed CMB likelihood, with and without DES-Y5 Type-Ia supernovae. Model I is driven to a markedly lower Hubble constant, H_0≃62.4,km,s^−1,Mpc^−1 for the combined data, and remains non-phantom with w_DE,0≃−0.814; it is strongly disfavoured relative to flat ΛCDM. Model II stays close to ΛCDM in the standard cosmological parameters and gives w_DE,0≃−1.003, while its two entropy-sector parameters remain strongly degenerate. Its best-fit likelihood is comparable to ΛCDM, but the additional parameters are not supported by information criteria. These results show that the two thermodynamic realizations of the same nonadditive entropy have sharply different phenomenological consequences at the homogeneous-background level. In summary, the observational plausibility of entropy-based cosmology hinges critically on how the generalized horizon entropy is incorporated into the Friedmann dynamics.
ER -