Non-Extensive Entropy and Power-Law Inflation: Implications for Observations

This study explores the interaction between non-extensive entropic FLRW cosmology and the power-law inflationary model, with a focus on the overlap between the scalar spectral index `$n_s$' and the tensor-to-scalar ratio `$r$'. Based on a conjecture that non-extensive entropy alters the energy-momentum content of the cosmic fluid, the analysis examines how these overlaps shift with different model parameters and compares the findings to those from Bekenstein-Hawking (BH) entropic cosmology. The study highlights the impact of Tsallis, R\'{e}nyi, and Sharma-Mittal entropies, uncovering a significant correlation between `$n_s$' and `$r$' that suggests a deeper connection in power-law inflationary dynamics. The results demonstrate that non-extensive entropies not only enable viable inflation with a graceful exit but also address limitations inherent in the standard BH entropic framework, emphasizing the importance of precise parameter estimation. Specifically, Tsallis entropy allows for power-law inflation with $n = 1$ to $n = 2$ in alignment with Planck 2018 data. Moreover, the $\alpha$ parameter in R\'{e}nyi and Sharma-Mittal entropy models must be extremely small ($\alpha \leq 10^{-8}$ in Planck mass units) to achieve successful power-law inflation with an e-folding number around 55-65, suggesting a unified thermodynamic perspective in cosmological studies.