Adiabatic And Entropy Perturations In Inflationary Models Based On Non-linear Sigma Model

The scalar perturbations in inflationary models, based on a two-component diagonal non-linear sigma model, are considered. For inhomogeneities generated at an inflationary stage, the law of motion of the comoving curvature ${\cal R}$ is obtained (without using the slow roll approximations). A formal expressions for the power spectrum and its spectral index are obtained, which are valid and after the slow-roll stage. As an example, an inflationary model with a massive scalar field and quadratic curvature corrections is studied numerically.