The impact of viscosity and anisotropy on cosmic expansion in [formula omitted] gravity

Abstract

In modified gravity theories, such as f(Q,T) gravity, the concept of dark energy arises from alterations to the gravitational field equations, often manifesting as purely geometrical effects. This perspective opens up intriguing possibilities, suggesting that a universe undergoing cosmic acceleration could be explained by a bulk viscous fluid coupled with a modified gravity theory. In this paper, we introduce a model describing the LRS Bianchi type-I spacetime filled with a viscous fluid within the framework of f(Q,T) gravity. By assuming that the universe is dominated by non-relativistic viscous matter, we derive an exact solution to the field equations for the Hubble parameter H(z) as a function of redshift z. We assess the viability of the proposed f(Q,T) model by fitting it to observational datasets and explore several key physical properties of our cosmological model, including the deceleration parameter, jerk parameter, anisotropy parameter, and Om(z) diagnostics. For the present-day values of the parameters, we obtain: zt=0.80−0.003+0.004, q0=−0.45±0.01, j0=0.63±0.12, and Δ=0.38±0.09 at the 1−σ confidence level. In addition, our findings indicate that our f(Q,T) model, dominated by bulk viscous dark energy, displays quintessence-like behavior according to the Om(z) diagnostic, with a negative slope across all redshift values. We conclude that our study contributes to a deeper understanding of cosmic dynamics and the role of viscosity in cosmological models.