Bulk viscous matter in $f(T)$ gravity: A path to cosmic acceleration

Abstract

In this paper, we investigate the effects of varying bulk viscosity coefficients $\hat{I}\P (t)=\hat{I}{\P }_0+\hat{I}{\P }_{1}H$ on cosmic evolution within the framework of $f(T)$ teleparallel gravity. We focus on two cases: (i) $\hat{I}{\P }_1\ne 0$ and (ii) $\hat{I}{\P }_1=0$, deriving the Hubble parameter $H$ as a function of redshift $z$ using a linear $f(T)$ model ($f(T)=\hat{I}\pm T$ where $\hat{I}\pm \ne 0$). Using the combined $H(z)+Pantheo{n}^{+}+BAO$ dataset, we obtain observational constraints on model parameters. For Case I ($\hat{I}{\P }_1\ne 0$), best-fit values are $H_0=60.0_{-1.9}^{+2.0}$ km/s/Mpc, $\hat{I}\pm =1.01_{-0.098}^{+0.10}$, $\hat{I}{\P }_0=40.1_{-2.0}^{+1.9}$, and $\hat{I}{\P }_1=0.123_{-0.088}^{+0.093}$, while for Case II ($\hat{I}{\P }_1=0$), they are $H_0=67.5_{-1.3}^{+1.3}$ km/s/Mpc, $\hat{I}\pm =0.94_{-0.13}^{+0.14}$, and $\hat{I}{\P }_0=34.7_{-2.0}^{+2.0}$. The analysis reveals a transition in the deceleration parameter, indicating a shift from deceleration to acceleration of the universe's expansion, with present-day values of $q_0\approx -0.49$ and $q_0\approx -0.32$ for the respective cases. The jerk parameter $j(z)$ and effective EoS for the cosmic viscous fluid also support the cosmic acceleration, with trajectories aligning with the quintessence scenario. These findings underscore the potential of our $f(T)$ model dominated by bulk viscous matter in explaining cosmic acceleration.

Physics Letters A accepted version