Constraining $f(Q,L_m)$ gravity with bulk viscosity

Abstract

We investigate the influence of bulk viscosity on late-time cosmic acceleration within an extended $f(Q,L_m)$ gravity framework, where the non-metricity $Q$ is non-minimally coupled with the matter Lagrangian $L_m$. Analyzing the function $f(Q,L_m)=\hat{I}\pm Q+{\hat{I}}^2{L}_m$, we derive exact solutions under non-relativistic matter domination. Using observational datasets ($H(z)$, Pantheon supernovae, and their combination), we constrain the model parameters $H_0$, $\hat{I}\pm$, ${\hat{I}}^2$, and $\hat{I}\P$. The deceleration parameter transitions from positive to negative values around redshifts $z_t\approx 0.80$ to $0.99$, indicating current accelerated expansion. Moreover, the effective equation of state parameter, $\ddot{I}{‰}_{eff}$, resembles quintessence dark energy ($-1<\ddot{I}{‰}_{eff}<-\frac{1}{3}$), with corresponding values from respective datasets. Finally, we use the $Om(z)$ diagnostic, which confirms that our model demonstrates quintessence-like behavior. Our findings underscore the significant role of bulk viscosity in understanding accelerated expansion in the universe within alternative gravity theories.

Minor revision in Physics of the Dark Universe