Cosmological Fluctuations of Short Wavelength
  This paper presents a completely analytic treatment of cosmological fluctuations whose wavelength is small enough to come within the horizon well before the energy densities of matter and radiation become equal. This analysis yields a simple formula for the conventional transfer function T(k) at large wave number k, which agrees very well with computer calculations of T(k). It also yields an explicit formula for the microwave background multipole coefficient C_ell at very large ell. 
Steven Weinberg