Scalar field dark energy models with a dynamical equation of state for matter

¹ Institute of Engineering & Management, School of University of Engineering and Management, Kolkata - 700091, India
² Meghnad Saha Institute of Technology, Nazirabad, Kolkata - 700150, India
³ St. Paul’s C. M. College, 33/1 Raja Rammohan Sarani, Kolkata - 700009, India

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 29 May 2026

Abstract

The red-shift z_eq, which signifies the termination of the radiation-dominated epoch and the onset of the matter-dominated era, can serve as an important diagnostic tool in reconstructing dark-energy models. In this work, we introduce a variable equation of state for matter that enables a smooth and continuous transition from radiation domination to matter domination within a single framework. This formulation allows estimation of z_eq in dark energy models and thereby facilitates assessment of their viability. To illustrate this approach, two one-parameter models involving minimally coupled scalar fields as dark energy are examined. We find that, although these models successfully reproduce the desired late-time cosmic behavior, the estimated value of z_eq exhibits strong sensitivity to the parameter value in each case.