Ghost dark energy in $f(R)$ model of gravity
  We study a correspondence between $f(R)$ model of gravity and a phenomenological kind of dark energy (DE), which is known as QCD ghost dark energy. Since this kind of dark energy is not stable in the context of Einsteinian theory of gravity and Brans-Dicke model of gravity, we consider two kinds of correspondence between modified gravity and DE. By studding the dynamical evolution of model and finding relevant quantities such as, equation of state parameter, deceleration parameter, dimensionless density parameter, we show that the model can describe the present Universe and also the EoS parameter can cross the phantom divide line without needs to any kinetic energy with negative sign. Furthermore, by obtaining the adiabatic squared sound speed of the model for different cases of interaction, we show that this model is stable.   Finally, we fit this model with supernova observational data in a non interaction case and we find the best values of parameter at $1\sigma$ confidence interval as; $f_0=0.958^{+0.07}_{-0.25}$, $\beta=-0,256^{+0.2}_{-0.1}$, and $\Om_{m_0} = 0.23^{+0.3}_{-0.15}$. These best-fit values show that dark energy equation of state parameter, $\om_{d_0}$, can cross the phantom divide line at the present time. 
Kh. Saaidi, Ali.Aghamohammadi, B. Sabet, O. Farooq
physics.gen-ph