Equation of State for Dark Energy in Modified Gravity Theories
  We explore the equation of state (EoS) for dark energy $w_{\mathrm{DE}}$ 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 $w_{\mathrm{DE}}=-1$ 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.
