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arXiv · 2507.14250

Constraints on R\'{e}nyi Entropy through Primordial Big-Bang Nucleosynthesis and Baryogenesis

Ahmad Sheykhi·Ava Shahbazi Sooraki
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Abstract

The R\'{e}nyi entropy, a one-parameter generalization of Boltzmann-Gibbs entropy, offers a promising framework for probing quantum gravitational effects in cosmology. By modifying the entropy-area relation of the apparent horizon, R\'{e}nyi entropy can alter the expansion dynamics of the early universe, with potential implications for Big-Bang Nucleosynthesis. In this work, we derive the modified Friedmann equations within the R\'{e}nyi entropy paradigm and investigate their impact on the primordial abundances of light elements Deuterium ($D$), Helium-4 ($_{}^{4}\textit{He}$), Lithium-7 ($_{}^{7}\textit{Li}$) and baryogenesis. Using observational constraints from Planck, primordial abundance data and observational data on baryogenesis, we put stringent bounds on the R\'{e}nyi parameter. Furthermore, we explore whether R\'{e}nyi entropy corrections could mitigate the long-standing Lithium discrepancy. This study provides the first systematic constraints on R\'{e}nyi cosmology from BBN and highlights the role of nonextensive thermodynamics in early-universe physics. Our analysis shows that the obtained ranges for the R\'{e}nyi parameter $\lambda$ exhibit a overlap for the Helium-4 and Deuterium, but this overlapping region-despite a small discrepancy-is inconsistent with the range obtained from Lithium-7. This small mismatch between the ranges raises the possibility of alleviating the \textit{Lithium Problem} in the modified cosmology scenarios. Furthermore, we present the relationship between the cosmic time and temperature within the framework of R\'{e}nyi cosmology. We observe that an increase in the R\'{e}nyi parameter increase the temperature of the early universe.

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Ahmad Sheykhi, Ava Shahbazi Sooraki. 2025-07-18. Constraints on R\'{e}nyi Entropy through Primordial Big-Bang Nucleosynthesis and Baryogenesis. https://doi.org/10.1016/j.dark.2026.102385

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