Equation of State for Dark Energy in Modified Gravity Theories

We explore the equation of state (EoS) for dark energy ω_DE in modified gravitational theories to explain the current accelerated expansion of the universe. We explicitly demonstrate that the future crossings of the phantom divide line of ω_DE = −1 are the generic feature in the existing viable f(R) gravity models. Furthermore, we show that the crossing of the phantom divide can be realized in the combined f(T) theory constructed with the exponential and logarithmic terms. In addition, we investigate the effective EoS for the universe when the finite-time future singularities occur in non-local gravity.