BLUE PERTURBATION SPECTRA FROM INFLATION

It is generally believed that inflationary models for the origin of primordial density perturbations predict a spectral index n less than or equal to 1. However, some observations, such as the first two years of COBE data, the Tenerife temperature anisotropy detection, bulk motions, and structures on the similar to 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.