Study of the cosmological tensions and DESI-DR2 in the framework of the Little Rip model

Abstract

We present an analysis that investigates the $H_0$ and $S_8$ tensions by considering a dark energy model. The latter is a late-time model characterized by a future abrupt event known as the Little Rip (LR) model and characterised by one extra parameter, $β$, compared to the standard model, $Λ$CDM. To test this approach, we perform a statistical analysis by the MCMC method using the most recent observational data. We obtain a positive correlation in ($H_0$, $β$) plane. We also note that the Hubble tension is less than $3σ$ when using early measurements, i.e., Cosmic Microwave Background (CMB) data, and when combining it with Baryon Acoustic Oscillation (BAO) data, but it is no longer so when we combine early and late measurements (i.e. PantheonPlus (PP)). In addition, we test the model with DESI-DR2 combined with CMB and recent SNIa measurements. We notice that our model shifts toward the quintessence field. For a complete statistical analysis, we use the Akaike Information Criteria and Bayesian analysis of the evidence. According to Bayes factors, we find that the LR model provides an improved fit only to CMB data.

Figures (5)

• Figure 1: A comparison of 1D posteriori distributions and 2D marginalized contours at $1\sigma$ and $2\sigma$ between $\Lambda$CDM (purple) and LR (blue), for all combinations of datasets: CMB (Top left panel), CMB+PP (Top right panel), CMB+BAO (bottom left panel) and CMB+BAO+PP (bottom right panel). The orange bands represent the local measurements of $H_0$ from SH0ES The parameter $\beta$ is expressed in units of [$\sqrt{\rho}$], where $\rho$ is the energy density and $H_0$ in [km s$^{-1}$ Mpc$^{-1}$]
• Figure 2: Functional posterior of $H(z)/(1+z)$, $\rho_{\text{de}}(z)/\rho_{\text{c,0}}$ and $w_{\text{de}}(z)$ plotted for the CMB-only and CMB+BAO+PP datasets for LR and $\Lambda$CDM models.
• Figure 3: 2D marginalized contours at 68% and 95% confidence levels on $S_8$ and $\beta$ ( The parameter $\beta$ is expressed in units of [$\sqrt{\rho}$], where $\rho$ is the energy density) for the LR model, plotted for CMB (in orange) and KV450+DES-Y1 (in blue). In addition, we present the value obtained by the combination of KV450 and DES-Y1 Joudaki_2020 (in red) and the Planck18 measurement aghanim2020planck (in green).
• Figure 4: The 1D posteriori distributions and 2D marginalized contours at $1\sigma$ and $2\sigma$ for the LR model, using CMB+DESI-DR2+Union3,CMB+DESI-DR2+DES-Y5 and CMB+DESI-DR2+PantheonPlus (left panel), where the parameter $\beta$ is expressed in units of [$\sqrt{\rho}$] and $H_0$ in [km s$^{-1}$ Mpc$^{-1}$]. The right panel shows the functional posterior of $w_{\text{de}}(z)$.
• Figure 5: The upper panel shows the CMB temperature power spectrum $C_{\ell}^{TT}$ and $\Delta C_{\ell}^{TT}/C_{\ell}^{TT}(\Lambda \text{CDM})$ . The lower panel represents the matter power spectrum $P(k)$ and $P(k)/P_{\Lambda \text{CDM}}(k)$, using the results obtained in Table (\ref{['T2']}).