We consider the problem of the initial conditions and behaviour of the
perturbations in scalar field cosmology with general potential.
We use the general definition of adiabatic and isocurvature conditions to set
the appropriate initial values for the perturbation in the scalar field and in
the ordinary matter and radiation components. In both the cases of initial
adiabaticity and isocurvature, we solve the Einstein and fluid equation at
early times and on superhorizon scales to find the initial behaviour of the
relevant quantities. In particular, in the isocurvature case, we consider
models in which the initial perturbation arises from the matter as well as from
the scalar field itself, provided that the initial value of the gauge invariant
curvature is zero.
We extend the standard code to include all these cases, and we show some
results concerning the power spectrum of the cosmic microwave background
temperature and polarization anisotropies. In particular, it turns out that the
acoustic peaks follow opposite behaviours in the adiabatic and isocurvature
regimes: in the first case their amplitude is higher than in the corresponding
pure cold dark matter model, while they make the opposite thing for pure
isocurvature initial perturbations.Comment: 21 pages, 8 figures, accepted for publication in Phys.Rev.
