The Atacama Cosmology Telescope: a measurement of the primordial power spectrum

TL;DR

This paper uses ACT data to measure the primordial power spectrum of adiabatic fluctuations, finding it consistent with a power-law over a wide scale range, and linking early universe fluctuations to late-time matter distribution.

Contribution

First to utilize ACT 2008 data for detailed constraints on the primordial power spectrum across multiple scales, confirming its power-law nature and connecting it with late-time matter observations.

Findings

No deviation from power-law fluctuations detected.

Primordial spectrum consistent with predictions over two decades in scale.

Overlap between CMB-inferred matter power and galaxy clustering data.

Abstract

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.