2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/5244Until now all well-studied dark energy models proposed have very large Compton wavelengths, $λ_c > 100 Mpc$ at all time and hence show no clustering on small scales. Evidence against this would disfavour both $Λ$CDM and quintessence. We show however, that large $λ_c$ is actually favoured by current CMB, LSS and SN1a data by comparing quintessence with a condensate scenario with the same background dynamics. The condensate scenario has a very small $λ_c$ before making a transition to negative pressure and large $λ_c$ and therefore exhibits a rich CMB phenomenology which roughly interpolates between $Λ$CDM and flat CDM models.5 pages, 3 colour eps figures. Related to a talk given by BB at the XVIIIth IAP Colloquium "On the nature of Dark Energy", Paris, July 2002AstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - Phenomenologytext