2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/53096Unified dark matter/energy models (quartessence) based upon the Chaplygin gas D-brane fail owing to the suppression of structure formation by the adiabatic speed of sound. Including string theory effects, in particular the Kalb-Ramond field which becomes massive via the brane, we show how nonadiabatic perturbations allow successful structure formation.9 pages, substantially expanded, arguments clarified, added references, results unchangedHigh Energy Physics - TheoryAstrophysicsGeneral Relativity and Quantum Cosmologytext