A novel dark energy model with an equation of state (EoS) given by: ω(z) = ω0 + ω1 z/(1 + ln(1 + z)) is proposed, which effectively captures the transition from deceleration to acceleration in the cosmic expansion. This model is motivated by recent observational measurements, all of which indicate a significant shift in the dynamics of the universe at intermediate redshifts (z ≈ 0.5). By utilizing a logarithmic damping term, the model allows for a smooth, redshift-dependent transition between matter, dark energy, and radiation domination, and avoids the abrupt transitions often observed in simpler models. In particular, the parameters ω0 and ω1 govern the early and late-time evolution of the equation of state. ω0 characterizes the late-time asymptotic behaviour, while ω1 controls the rate of transition at intermediate redshifts. The model is further examined from multiple theoretical standpoints: we establish its correspondence with viscous and logotropic dark fluids, reconstruct its scalar field theoretical counterpart (quintessence-type), and derive the effective equation of state ωeff (z), which confirms a smooth transition to an accelerating phase near z ~ 0.5. Furthermore, we perform a thermodynamic analysis to verify the validity of the generalized second law of thermodynamics (GSL) and ensure the model′s stability. The speed of sound, which is essential for stability analysis, is computed and analysed to ensure it remains positive and stable across all redshifts, ensuring that the model adheres to physical constraints. We analysed the present model with updated observational Hubble parameter data from cosmic chronometers, performing a full chi-square minimization and model selection analysis using the Akaike Information Criterion (AIC). The resulting best-fit parameters indicate a close match with data, yielding a <InlineEquation ID="IEq1"> <EquationSource Format="TEX">${\chi }_{min}^{2}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>χ</mi> <mrow> <mi mathvariant="italic">min</mi> </mrow> <mn>2</mn> </msubsup> </math></EquationSource> </InlineEquation> comparable to ΛCDM and CPL, and a ∆AIC that confirms the present model as a competitive phenomenological alternative within the current cosmological framework.

A Novel Parametrized Dark Energy Model in a Flat Universe

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发表日期：

2025年9月1日

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C. Sivakumar

摘要

A novel dark energy model with an equation of state (EoS) given by: ω(z) = ω₀ + ω₁ z/(1 + ln(1 + z)) is proposed, which effectively captures the transition from deceleration to acceleration in the cosmic expansion. This model is motivated by recent observational measurements, all of which indicate a significant shift in the dynamics of the universe at intermediate redshifts (z ≈ 0.5). By utilizing a logarithmic damping term, the model allows for a smooth, redshift-dependent transition between matter, dark energy, and radiation domination, and avoids the abrupt transitions often observed in simpler models. In particular, the parameters ω₀ and ω₁ govern the early and late-time evolution of the equation of state. ω₀ characterizes the late-time asymptotic behaviour, while ω₁ controls the rate of transition at intermediate redshifts. The model is further examined from multiple theoretical standpoints: we establish its correspondence with viscous and logotropic dark fluids, reconstruct its scalar field theoretical counterpart (quintessence-type), and derive the effective equation of state ω_eff (z), which confirms a smooth transition to an accelerating phase near z ~ 0.5. Furthermore, we perform a thermodynamic analysis to verify the validity of the generalized second law of thermodynamics (GSL) and ensure the model′s stability. The speed of sound, which is essential for stability analysis, is computed and analysed to ensure it remains positive and stable across all redshifts, ensuring that the model adheres to physical constraints. We analysed the present model with updated observational Hubble parameter data from cosmic chronometers, performing a full chi-square minimization and model selection analysis using the Akaike Information Criterion (AIC). The resulting best-fit parameters indicate a close match with data, yielding a ${\chi }_{min}^{2}$ $χ_{\min}^{2}$ comparable to ΛCDM and CPL, and a ∆AIC that confirms the present model as a competitive phenomenological alternative within the current cosmological framework.