The Atacama Cosmology Telescope: a measurement of the primordial power
  spectrum
  We present constraints on the primordial power spectrum of adiabatic
fluctuations using data from the 2008 Southern Survey of the Atacama Cosmology
Telescope (ACT). The angular resolution of ACT provides sensitivity to scales
beyond \ell = 1000 for resolution of multiple peaks in the primordial
temperature power spectrum, which enables us to probe the primordial power
spectrum of adiabatic scalar perturbations with wavenumbers up to k \simeq 0.2
Mpc^{-1}. We find no evidence for deviation from power-law fluctuations over
two decades in scale. Matter fluctuations inferred from the primordial
temperature power spectrum evolve over cosmic time and can be used to predict
the matter power spectrum at late times; we illustrate the overlap of the
matter power inferred from CMB measurements (which probe the power spectrum in
the linear regime) with existing probes of galaxy clustering, cluster
abundances and weak lensing constraints on the primordial power. This
highlights the range of scales probed by current measurements of the matter
power spectrum.
