Black Holes from Blue Spectra
  Blue primordial power spectra with a spectral index $n>1$ can lead to a significant production of primordial black holes in the very early Universe. The evaporation of these objects leads to a number of observational consequences and a model independent upper limit of $n \approx 1.4$. In some cases this limit is strengthened to $n=1.3$. Such limits may be employed to define the boundary to the region of parameter space consistent with generalized inflationary predictions. [To appear in Proceedings of the CASE WESTERN CMB WORKSHOP, April 22-24 1994. Figures available on request from J.H.Gilbert@qmw.ac.uk] 
James E. Lidsey, B.J. Carr & J.H. Gilbert