Blue perturbation spectra from inflation

It is generally believed that inflationary models for the origin of primordial density perturbations predict a spectral index n{≤}1. However, some observations, such as the first two years of COBE data, the Tenerife temperature anisotopy detection, bulk motions, and structures on the {~}50h^-1 Mpc scale, have recently aroused much interest in spectral indices n>1 (``blue spectra''). We show that there is a class of inflationary models leading to this kind of spectra: they are produced while the inflaton field rolls down to a potential minimum with the potential energy dominated by a cosmological-constant-like piece.