Bulk viscous cosmological model in f(T,T) modified gravity

Abstract

This article explores the impact of bulk viscosity on understanding the universe’s accelerated expansion within the context of modified $f(T,T)$ gravity, which is an extension of the $f\left(T\right)$ gravitational theory, allowing a broad coupling between the energy–momentum scalar $T$ and the torsion scalar $T$. We consider two $f(T,T)$ functions, specifically $f(T,T)=\alpha T+\beta T$ and $f(T,T)=\alpha \sqrt{-T}+\beta T$, where $\alpha$ and $\beta$ are arbitrary constants, along with the fluid part incorporating the coefficient of bulk viscosity $\zeta ={\zeta }_0>0$. We calculate the analytical solutions of the corresponding field equations for a flat FLRW environment, and then we constrain the free parameters of the obtained solution using CC, Pantheon+, and the CC+Pantheon+ samples. We perform the Bayesian statistical analysis to estimate the posterior probability utilizing the likelihood function and the MCMC random sampling technique. Further, to assess the effectiveness of our MCMC analysis, we estimate the corresponding AIC and BIC values, and we find that there is strong evidence supporting the assumed viscous modified gravity models for all three data sets. Also, we find that the linear model precisely mimics the $\Lambda$CDM model. We also investigate the evolutionary behavior of some prominent cosmological parameters. We observe that the effective equation of state parameter for both models predict the accelerating behavior of the cosmic expansion phase. In addition, from the statefinder test, we find that the parameters of the considered MOG models favor the quintessence-type behavior. Further, we observe that the behavior of $Om\left(z\right)$ curves corresponding to both models represent a consistent negative slope across the entire domain. We infer that our cosmological setting utilizing $f(T,T)$ gravity models with the viscous matter fluid embodies quintessence-like behavior and can successfully describe the late-time scenario.