Bulk viscous matter and the cosmic acceleration of the universe in $f(Q,T)$ gravity

TL;DR

This paper explores how bulk viscosity within $f(Q,T)$ gravity can explain the universe's accelerated expansion, fitting observational data and showing consistency with current cosmological models.

Contribution

It introduces an exact solution in $f(Q,T)$ gravity with bulk viscosity, constrained by observational datasets, and demonstrates its compatibility with the universe's accelerated expansion.

Findings

The model fits well with Hubble, BAO, and Pantheon datasets.

The universe transitions from deceleration to acceleration.

The effective dark energy from bulk viscosity explains current acceleration.

Abstract

We have studied bulk viscosity in the modified $f(Q, T)$ gravity theory formalism, where $Q$ represents the non-metricity and $T$ denotes the trace of energy-momentum tensor within a flat Friedmann-Lema\^{i}tre-Robertson-Walker metric (FLRW). Here, we have explicitly considered the effective equation of state, which includes a bulk viscosity term, and obtained the exact solutions by assuming a specific form of $f(Q, T)=\alpha Q+\beta T$, where $\alpha$ and $\beta$ are constants. Furthermore, we have found constraints on the model parameters with some external datasets, such as the revised Hubble datasets consisting of 57 data points, Baryon acoustic oscillations (BAO) datasets, and the newly published Pantheon samples with 1048 points to obtain the best fitting values of the model parameters. The obtained model is found to be in good agreement with observations. In addition, we have analyzed the cosmological behavior of the density parameter, the equation of state (EoS) parameter ($\omega$), and the deceleration parameter ($q$). The results are satisfying to the standard scenario of recent findings of cosmology. The universe appears to be evolving from a decelerated to an accelerated phase. The EoS parameter is further in the quintessence phase, indicating that the universe is accelerating. Finally, we can deduce that the accumulation of bulk viscosity as effective dark energy supports the current accelerated expansion of the universe.