Testing Viability of Hubble Parametrizations in f(R,T) Kaluza-Klein Gravity: A Stability Analysis

S. R. Bhoyar*

Received : November 22, 2025 | Published : January 05, 2026

Citation: S. R. Bhoyar, “Testing viability of Hubble parametrizations in f(R,T) Kaluza–Klein gravity: A stability analysis,” Phys. J. Theor. Exp. Stud. 2(1), 1–16 (2026). DOI: 10.64978/pjtes.2026.0105002

Abstract

While various parametrizations of the Hubble parameter have been proposed to model the universe’s expansion, their viability within higher-dimensional modified gravity remains largely untested. This study rigorously investigates the cosmological dynamics of five distinct Hubble models (hyperbolic tangent, logarithmic, power-law, exponential decay, and emergent) within a Kaluza-Klein f(R,T)gravity framework. Crucially, beyond standard kinematic evolution, we subject these models to a comprehensive stability analysis using the squared speed of sound and energy condition constraints. We demonstrate that while most parametrizations can successfully mimic late-time cosmic acceleration, only the Logamediate Model (Model III) maintains perturbative stability throughout the cosmic history. This work establishes a critical selection criterion for modified gravity reconstructions, filtering out observationally consistent but theoretically unstable dark energy candidates.

Keywords: FRW type Kaluza Klein Universe, Hubble Parameters, Modified Gravity, Stability, Energy conditions