The first two are evaluated 55 efolds before the end of inflation and the cosmic string tension comes from the end of inflation when the waterfall field condenses . First , we find that the spectral index is 0.98 which is within ∼ 2σ range of WMAP3 year data [ 30 ] . The power spectrum is measured to be P R ∼ 10 −9 from which we get that the scale of inflation is of order of the GUT scale