Hamilton-Jacobi Approach to Inflationary Scenarios through Extended Entropies: An Observational Perspective

Abstract

The slow-roll inflation paradigm can be systematically generalized within the framework of non-standard entropy formalisms, giving rise to a broad class of inflationary models that deviate from the conventional Bekenstein--Hawking case. We adopt a pragmatic observational strategy, employing the Hamilton--Jacobi formalism to establish a direct link between the inflationary potential, the generalized entropy function, and the resulting cosmological observables. In this approach we introduce a novel non-linear parametrization of the Hubble parameter, yielding sensible results, including consistency with recent observational data and new estimates of the cosmological parameters of the generalized entropy framework: the Tsallis parameter $δ\simeq1.1-1.2$, the Rényi parameter $α\sim\mathcal{O}(10^{-14})$, and the Kaniadakis statistics parameter $K\sim\mathcal{O}(10^{-17})$. Our analysis proceeds in two regimes: first, by constraining models directly with the primary inflationary parameters including the scalar spectral index ($n_s$) and the tensor-to-scalar ratio ($r$); second, by exploring the impact of the observational uncertainty on the upper bound of $r$ ($σ_r$), which we vary to assess its influence on parameter estimation. This dual approach yields complementary posterior distributions that restrict the viable parameter space of entropy-based inflationary models. We further highlight the implications of the Hamilton--Jacobi method for the dynamics of the inflationary epoch, the reheating process, and, as a secondary objective, the subsequent evolution of cosmic structure in the late universe.