Observational constraints and stability in viscous f(T, T) gravity

In this paper, we study the f(T, T) gravity model in the presence of bulk viscosity by the flat Friedmann-Robertson-Walker metric. The field equation is obtained by teleparallel gravity with a tetrad field. The universe components are considered matter and dark energy, with the dark energy component associated with viscous f(T, T) gravity. After calculating the Friedmann equations, we obtain the energy density, pressure, and equation of state of dark energy in terms of the redshift parameter. Afterward, we plot the corresponding cosmological parameters versus the redshift parameter and examine the accelerated expansion of the universe. In the end, we explore the system stability using a function called the speed sound parameter.