Quintessence with a constant equation of state in hyperbolic universes
  Quintessence models leading to a constant equation of state are studied in hyperbolic universes. General properties of the quintessence potentials V(phi) are discussed, and for some special cases also the exact analytic expressions for these potentials are derived. It is shown that the observed angular power spectrum of the cosmic microwave background (CMB) is in excellent agreement with some of the quintessence models even in cases with negative curvature. It is emphasized that due to a (w_phi, Omega_phi, Omega_c)-degeneracy a universe with negative spatial curvature cannot be excluded. 
R. Aurich and F. Steiner