We explore an extension of the symmetric teleparallel gravity denoted the f( Q) theory, by considering a function of the nonmetricity invariant Qas the gravitational Lagrangian. Some interesting...

We investigate observational constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy from the latest observational data: the Union SNe Ia data, the observational Hubble data, the SDSS baryon acoustic peak and the five-year WMAP shift parameter. The result is obtained that the best-fit values of the GCG model parameters with their confidence level are A _s=0.73 _−0.06 ^+0.06 (1σ) _−0.09 ^+0.09 (2σ), α=−0.09 _−0.12 ^+0.15 (1σ) _−0.19 ^+0.26 (2σ). Furthermore, in this model, we can see that the evolution of equation of state (EOS) for dark energy is similar to quiessence, and its current best-fit value is w _0de=−0.96 with the 1σ confidence level −0.91≥w _0de≥−1.00.

In a spatially flat Friedmann-Lemaître-Robertson-Walker universe, we investigate a unified cosmic fluid scenario endowed with bulk viscosity in which the coefficient of the bulk viscosity has a power law evolution. The power law in the bulk viscous coefficient is a general case in this study which naturally includes several choices as special cases. Considering such a general bulk viscous scenario, in the present work, we have extracted the observational constraints using the latest cosmological datasets and examine their behavior at the level of both background and perturbations. From the observational analyses, we find that a nonzero bulk viscous coefficient is always favored and some of the models in this series are able to weaken the current tension on $H_0$ for some dataset. However, from the Bayesian evidence analysis, $\mathrm{\Lambda }$ cold dark matter is favored over the bulk viscous model.