Late-time cosmology in $f(Q, L_m)$ gravity: Analytical solutions and observational fits

Abstract: In this study, we examined the late-time cosmic expansion of the universe within the framework of $f(Q, L_m)$ gravity, where $Q$ denotes the non-metricity and $L_{m}$ represents the matter Lagrangian. We analyzed a linear $f(Q, L_m)$ model of the form $f(Q, L_m) = -\alpha Q + 2 L_{m} + \beta$. Using MCMC methods, we constrained the model parameters $H_0$, $\alpha$, and $\beta$ with various datasets, including $H(z)$, Pantheon+SH0ES, and BAO data. For the $H(z)$ dataset, we found $H_0 = 67.90 \pm 0.66$, $\alpha = 0.1072_{-0.0069}^{+0.0054}$, and $\beta = -1988.2 \pm 1.0$. For the Pantheon+SH0ES dataset, $H_0 = 70.05 \pm 0.68$, $\alpha = 0.0916_{-0.0033}^{+0.0028}$, and $\beta = -1988.3 \pm 1.0$. For the BAO dataset, $H_0 = 68.1 \pm 1.0$, $\alpha = 0.1029_{-0.0052}^{+0.0041}$, and $\beta = -1988.24 \pm 0.99$. Moreover, the energy density remains positive and approaches zero in the distant future, and the deceleration parameter indicates a transition from deceleration to acceleration, with transition redshifts of $z_t = 0.60$, $z_t = 0.78$, and $z_t = 0.66$ for the respective datasets. These findings align with previous observational studies and contribute to our understanding of the universe's expansion dynamics.