$w_{dm}$-$w_{de}$ cosmological model with new data samples of cosmological observations

TL;DR

This work investigates a w\_dm–w\_de cosmology where dark matter and dark energy obey barotropic equations of state, extending beyond ΛCDM by allowing $w_{dm}\neq 0$ and $w_{de}\neq -1$ in both flat and curved geometries. A dynamical-systems formalism identifies equilibrium points and bifurcations that govern radiation-, matter-, and dark-energy-dominated epochs, as well as scaling and Einstein static-like states. The model is constrained with updated data (OHD, Pantheon+, SLS, BAO, CMB) in a Bayesian framework, with AIC/BIC used to compare to ΛCDM; results show consistency with ΛCDM within $3\sigma$ but also reveal mild deviations and the potential for competitive curved-model fits, hinting at warm dark matter and quintessence-like dark energy in some cases. Overall, ΛCDM remains preferred without curvature, but curvature-enabled w\_dm–w\_de scenarios provide valuable insights into the dark sector and cosmic evolution, motivating further observational and theoretical exploration of non-standard EoS cosmologies.

Abstract

We revisit a cosmological model where dark matter (DM) and dark energy (DE) follow barotropic equations of state, allowing deviations from the standard $Λ$CDM framework (i.e. $w_{dm} \neq 0$, $w_{de} \neq -1$), considering both flat and non-flat curvature. Using a dynamical system approach, we identify equilibrium states that govern stability, expansion, and contraction. Expansion occurs when $H>0$, while contraction is linked to $H < 0$. Accelerated expansion arises from DE dominance, whereas radiation- and matter-dominated phases lead to deceleration. Some solutions are unphysical due to density constraints, but viable cases offer insights into cosmic transitions, including the Einstein static universe, which allows for shifts between accelerating and decelerating phases. We perform a Bayesian analysis with updated datasets, including observational Hubble data, Pantheon+ Type Ia supernovae, strong lensing systems, baryon acoustic oscillations and cosmic microwave background, to constrain the parameters $w_{dm}$ and $w_{de}$. Our results from the data joint analysis show consistency with $Λ$CDM within $3σ$, but none of the cases reproduce $w_{dm} = 0$ and $w_{de} = -1$. Nevertheless, the comparison with the standard model using the Akaike and Bayesian information criteria indicates that only the non-flat scenario has the potential to be competitive. This suggests that a non-dust-like DM may impact structure formation, while DE could shift toward quintessence fluid. While $Λ$CDM remains a strong model, our findings indicate that alternative dark sector models with non-standard EoS could be viable and offer new insights into cosmic evolution.

Figures (9)

• Figure 1: $\Omega_{de}$-$\Omega_{r }$ phase planes of system \ref{['ds2']} for $w_{de}= -1, -2/3, -1/3$.
• Figure 2: Phase space of system \ref{['systA']} for $(w_{de},w_{dm})= (-1,0), (-2/3, 0.2), (-1/3, 0.2)$.
• Figure 3: Phase space of system \ref{['Phase-Space3Dnegativek']} for $k=-1$ and $w_{de}= -1, -2/3, -1/3$.
• Figure 4: Some trajectories of system \ref{['system_positive_curvature']} using initial conditions from table \ref{['tab:ini2']} and setting $w_{de}=0.753217$ and $w_{dm}=0.0439285$. It shows the crossing through $H=0$ and the center behavior of $S_1$. This behavior, corresponding to cyclic cosmology, is nonphysical since it requires $\hat{\Omega }_{r}<0$.
• Figure 5: Some trajectories of system \ref{['system_positive_curvature']} using initial conditions from table \ref{['tab:ini']} and setting $w_{de}=0.7$ and $w_{dm}=0.3$. It shows the crossing through $H=0$.