Analytic Results for a Flat Universe Dominated by Dust and Dark Energy
  We find the solution for the scale factor in a flat Universe driven by dust plus a component characterized by a constant parameter of state which dominates in the asymptotic future. We also present an analytic formula (in terms of hypergeometric functions) for the past light cone in such a universe. As applications of this result, we give analytic expressions for the Luminosity Distance and for the Acoustic Scale, where the latter determines the peaks positions in the pattern of CMB anisotropies. 
A.Gruppuso and F.Finelli