Equation of state for dark energy in $f(T)$ gravity
  We study the cosmological evolutions of the equation of state for dark energy
$w_{\mathrm{DE}}$ in the exponential and logarithmic as well as their
combination $f(T)$ theories. We show that the crossing of the phantom divide
line of $w_{\mathrm{DE}} = -1$ 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 $w_{\mathrm{DE}} > -1$ to $w_{\mathrm{DE}} <
-1$, in the opposite manner from $f(R)$ gravity models. We also demonstrate
that this feature is favored by the recent observational data.
