Early time perturbations behavior in scalar field cosmologies - art. no. 123508

We consider the problem of the initial conditions and behavior of the pertu rbations in scalar field cosmology with a general potential. We use the gen eral definition of adiabatic and isocurvature conditions to set the appropr iate initial values for the perturbation in the scalar field and in the ord inary matter and radiation components. Tu both the cases of initial adiabat icity and isocurvature, we solve the Einstein and fluid equations at early times and on superhorizon scales to find the initial behavior of the releva nt quantities. In particular, in the isocurvature case, we consider models in which the initial perturbation arises from the matter as well as from th e scalar held itself, provided that the initial value of the gauge-invarian t 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 micr owave background temperature and polarization anisotropies. Tn particular, it turns out that the acoustic peaks follow opposite behavior in the adiaba tic and isocurvature regimes: in the first case their amplitude is higher t han in the corresponding pure cold dark matter model, while it is the oppos ite for pure isocurvature initial perturbations. [S0556-2821(99)03110-0].