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arXiv · 2512.19000

$\mathbf{Ω_1Ω_2}$-$\mathbfΛ$CDM: A promising phenomenological extension of the standard model of cosmology

Suresh Kumar
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Abstract

We investigate a phenomenological extension of the standard $Λ$CDM framework, the $Ω_1Ω_2$-$Λ$CDM model, in which the total energy density of the universe is expanded in powers of $1+z$. This parameterization recovers $Λ$CDM and introduces two additional terms, $Ω_1(1+z)$ and $Ω_2(1+z)^2$, in the dark energy sector alongside the cosmological constant, leading to a physically interpretable and observationally testable effective dark energy dynamics. Using Planck cosmic microwave background (CMB) data, we find that the model allows additional freedom in the late-time expansion history while preserving standard early-universe physics. When DESI baryon acoustic oscillation (BAO) data are included, the inferred Hubble constant is $H_0 = 69.74 \pm 0.77~\mathrm{km\;s^{-1}\;Mpc^{-1}}$ (68% CL), consistent with Tip of the Red Giant Branch (TRGB) measurements from the Carnegie--Chicago Hubble Program (CCHP). The reconstructed dark energy equation of state exhibits a smooth transition across the phantom divide followed by asymptotic de Sitter behavior, modifying late-time dynamics while maintaining standard early-time cosmology. Overall, controlled late-time deviations from $Λ$CDM improve cosmological concordance.

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Suresh Kumar. 2026-02-19. $\mathbf{Ω_1Ω_2}$-$\mathbfΛ$CDM: A promising phenomenological extension of the standard model of cosmology. https://doi.org/10.1016/j.dark.2026.102248

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