•
•If
there are entropy perturbations such
that the pressure perturbation
δp=0 and with it the
acoustic horizon ds=0, no
problem arises
• R.R.R. Reis, I. Waga, M.O. Calvão, and S.E. Joŕas,
PRD 68 (2003)
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•
• The scenario with entropy perturbations, which is difficult to justify in the simple Chaplygin gas model, may be realized by introducing an extra degree of freedom, e.g., in terms of a quintessence-type scalar field φ
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•