Evolution of the spectral index after inflation
  In this article we investigate the time evolution of the adiabatic(curvature)
and isocurvature (entropy) spectral indices after end of inflation for all
cosmological scales and two different initial conditions. For this purpose,we
first extract an explicit equation for the time evolution of the comoving
curvature perturbation (which may be known as the generalized Mukhanov-Sasaki
equation). It shall be manifested that the evolution of adibatic spectral index
severely depends on the intial conditions and just for the super-Hubble scales
and adiabatic initial conditions is constat as be expected.Moreover,it shall be
clear that the adiabatic spectral index after recombination approach to a
constant value for the isocurvature perturbations.Finally,we re-investgate the
Sachs-Wolfe effect and show that the fudge factor 1/3 in the adiabatic ordinary
Sachs-Wolfe formula must be replaced by 0.4.
