Observational Constraints on Plane Symmetric Renyi Holographic Dark Energy Universe with Scalar Fields and Cosmic Strings

In this work, we investigate a cosmological model based on a plane symmetric space–time, where the matter content of the Universe is described by Rényi holographic dark energy within the framework of Einstein’s theory of gravitation in the presence of massive scalar fields and cosmic strings. Exact solutions of the field equations are obtained by assuming a specific relation between the metric potentials. Observational constraints on the model parameters are obtained using the latest Hubble cosmic chronometer data through a Markov Chain Monte Carlo analysis. The resulting contour plots provide tight bounds on the free parameters, and the reconstructed Hubble parameter exhibits excellent agreement with the ΛCDM model over the entire redshift range. A detailed investigation of the cosmological parameters reveals that the model successfully reproduces the standard cosmic evolution. The deceleration parameter indicates a matter-dominated, decelerating phase at early epochs (z ≥ 2), followed by a smooth transition to the present accelerated phase and an asymptotic approach to a de Sitter–like expansion in the future. The dark energy equation-of-state parameter evolves dynamically and crosses the phantom divide, exhibiting quintom-like behavior. The ωde - ω'de plane analysis places the model predominantly in the freezing region, indicating a stable and rapidly accelerating dark energy phase. Statefinder diagnostics show consistency with ΛCDM at the present epoch, with deviations toward Chaplygin gas–like behavior at late times. Furthermore, the energy condition analysis supports the accelerated expansion through the violation of the strong energy condition at late times. Overall, the model provides a physically viable and observationally consistent description of cosmic evolution beyond the standard ΛCDM scenario.