Quintom-like transit universe models in Metric-affine $f(R,T,Q,T_m)$ gravity

TL;DR

This work develops Quintom-like transit universe models within metric-affine f(R,T,Q,T_m) gravity by adopting a linear f form and solving the modified Friedmann equations for a flat FLRW universe. Using MCMC analysis on cosmic chronometers and Pantheon data, the authors constrain the parameters (H0, γ, α, β) and show a hyperbolic Hubble evolution, with ω_eff and ω_de indicating a quintom-A evolution and phantom-like Om diagnostics. They find a transition redshift z_t ≈ 0.5–1.2 and an age t0 ≈ 13.9 Gyr, with H0 values in the 65–69 km/s/Mpc range, consistent with current observations. The results demonstrate that metric-affine f(R,T,Q,T_m) gravity can reproduce quintom-like cosmic evolution without a cosmological constant, highlighting its potential to describe the universe’s full history within a single geometric framework.

Abstract

The current transit universe model is a precise solution to the equations of a new type of gravity theory called metric-affine $f(R,T,Q,T_m)$ gravity proposed in [Herko et al. \textit{Phys. Dark Univ.} \textbf{34} (2021) 100886]. This theory is the maximal extension of the most successful theory, ``General Relativity," by including the scalars, Ricci curvature $R$, torsion $T$, nonmetricity $Q$, and trace $T_{m}$ of the matter-energy-momentum tensor using a generalized connection called the ``metric-affine" connection. We obtain the modified field equations for a linear form of the $f(R,T,Q,T_m)$ function and for a flat, homogeneous, and isotropic FLRW spacetime universe. We find a hyperbolic solution and determine the constrained values of the model parameters using the latest observational data. We examine how certain cosmological factors, like the deceleration parameter $q(z)$, effective equation of state parameter $ω_{\rm eff}$, and dark energy equation of state parameter $ω_{\rm de}$, vary over time to explain the properties of the observable universe. We perform the $Om$ diagnostic test for the model, and it represents the phantom scenarios of the model. The behavior of the dark energy EoS parameter $ω_{\rm de}$ reveals the quintom-A-type universe characteristics.

Figures (6)

• Figure 1: 2D contour plots of $H_{0}, \gamma$ using MCMC analysis of $31$ CC dataset.
• Figure 2: 2D contours of $H_{0}$, $\gamma$ and $\mathcal{M}$ at $\sigma1$ and $\sigma2$ confidence level for CC+Pantheon datasets.
• Figure 3: The variation of effective EoS parameter $\omega_{\rm eff}$ versus $z$.
• Figure 4: The variation of dark energy EoS parameter $\omega_{\rm de}$ versus $z$.
• Figure 5: The variation of deceleration parameter $q(z)$ versus $z$.