Probing the dark energy with redshift space quasar clustering distortion
  We have run Monte Carlo simulations, for quasar clustering redshift distortions in the Two-Degree Field QSO Redshift Survey (2QZ), in order to elicit the power of redshift distortions (geometric Alcock-Paczynski and linear kinematic) to constrain the cosmological density and equation of state parameters, Omega_{m0}, Omega_{x0}, w, of a pressureless matter + dark energy model. It turns out that, for the cosmological constant case (w = -1), the test is especially sensitive to the difference Delta := Omega_{m0} - Omega_{Lambda 0}, whereas for the spatially flat case (k = 0), it is quite competitive with SNAP and DEEP, besides being complimentary to them; furthermore, we find that, whereas not knowing the actual value of the bias does not compromise the correct recovering of Delta, taking into account the linear velocity effect is absolutely relevant, all within the 2 sigma confidence level. 
M. O. Calvao, J. R. T de Mello Neto and I. Waga