Brute force reconstruction of the primordial fluctuation spectrum from five-year Wilkinson Microwave Anisotropy Probe observations

Abstract

The primordial fluctuation spectrum is reconstructed from the five-year Wilkinson Microwave Anisotropy Probe data of the cosmic microwave background anisotropy. We divide the wave number space in the range of $1.23\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}\ensuremath{\lesssim}k\ensuremath{\lesssim}2.76\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ into about 50 bins, and derive probability distributions of fluctuation amplitudes on the respective scales using Monte Carlo simulations. Although the reconstructed spectrum is basically consistent with a power-law spectrum, we find a hint of fine structure at $k\ensuremath{\approx}0.002\text{ }\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ and $0.009\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$. The former is observed only in the temperature anisotropy, while the latter is both in the temperature and polarization anisotropies. The significance of these features are discussed, and it is shown that the deviation from a power-law spectrum at $k\ensuremath{\approx}0.009\text{ }\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ is at $2.8\ensuremath{\sigma}$ level.