Fluctuations in the cosmic microwave background. II.Clat large and smalll

Steven Weinberg
2001 Physical Review D, Particles and fields  
General asymptotic formulas are given for the coefficient C_ℓ of the term of multipole number ℓ in the temperature correlation function of the cosmic microwave background, in terms of scalar and dipole form factors introduced in a companion paper. The formulas apply in two overlapping limits: for ℓ≫ 1 and for ℓ d/d_A≪ 1 (where d_A is the angular diameter distance of the surface of last scattering, and d is a length, of the order of the acoustic horizon at the time of last scattering, that
more » ... terizes acoustic oscillations before this time.) The frequently used approximation that C_ℓ receives its main contribution from wave numbers of order ℓ/d_A is found to be less accurate for the contribution of the Doppler effect than for the Sachs--Wolfe effect and intrinsic temperature fluctuations. For ℓ d/d_A≪ 1 and ℓ≥ 2, the growth of C_ℓ with ℓ is shown to be affected by acoustic oscillation wave numbers of all scales. The asymptotic formulas are applied to a model of acoustic oscillations before the time of last scattering, with results in reasonable agreement with more elaborate computer calculations.
doi:10.1103/physrevd.64.123512 fatcat:wfhcxkwqkjbmtk5p2ywuonkxv4