How to Test Stringy Dark Energy?
  It is suggested, by using a covariant lagrangian formalism to estimate the equation of state $w = p/\rho$, that stringy dark energy predicts $w < -1$, a negative pressure larger in magnitude than that for a cosmological constant or quintessence. This would lead to a later transition from decelerating to accelerating cosmological expansion; $w = - 4/3$ is briefly considered as one illustrative example. 
P.H. Frampton