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

License: This article is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0) , which permits use, sharing, adaptation, distribution, and reproduction in any medium or format, provided appropriate credit is given to the original author(s) and the source, a link to the Creative Commons licence is provided, and any changes made are indicated.

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