Scalar perturbations in a primordial inflationary scenario

We compute the spectral index for scalar perturbations generated in a primordial inflationary model. In this model, the transition of the inflationary phase to the radiative era is achieved through the decay of the cosmological term leading to a second order phase transition and the characteristics of the model allow us to implement a set of initial conditions where the perturbations display a thermal spectrum when they emerge from the horizon. The obtained value for the spectral index is equal to 2, a result that depends very weakly on the various parameters of the model and on the initial conditions used. So as it stands the model is in contradiction with observations and pleads for the usual scalar-field inflation. Nevertheless, we conclude by suggesting some ways to amend the model and reconcile it with the usual value of the spectral indice: 1.