Equation of state for dark energy in f ( T ) gravity

We study the cosmological evolutions of the equation of state for dark energy w DE in the exponential and logarithmic as well as their combination f ( T ) theories. We show that the crossing of the phantom divide line of w DE = −1 can be realized in the combined f ( T ) theory even though it cannot be in the exponential or logarithmic f ( T ) theory. In particular, the crossing is from w DE > −1 to w DE < −1, in the opposite manner from f ( R ) gravity models. We also demonstrate that this feature is favored by the recent observational data.