Viscous Fluids and Gauss-Bonnet Modified Gravity

We study effects of cosmic fluids on finite-time future singularities in modified $f(R,G)$-gravity, where $R$ and $G$ are the Ricci scalar and the Gauss-Bonnet invariant, respectively. We consider the fluid equation of state in the general form, $\omega =\omega (\rho )$, and we suppose the existence of a bulk viscosity. We investigate quintessence region ($\omega >-1$) and phantom region ($\omega <-1$) and the possibility to change or avoid the singularities in $f(R,G)$-gravity. Finally, we study the inclusion of quantum effects in large curvatures regime.