When I read explanations about the early Universe and the oscillations of the photon-baryon fluid before recombination, effects of the cosmological constant and of the curvature of the Universe on the fluid are never discussed. Only dark matter, baryons, and photons are mentionned. Dark energy and curvature have no impact on the fluid ? I'm just looking for a simple answer, with at most some qualitative explanation if someone has that. The maths involved in the baryon-photon fluid oscillations are quite hard to tackle for me.