The primordial matter power spectrum on sub-galactic scales

TL;DR

This study uses gravitational lensing of quasars to measure the small-scale primordial matter power spectrum, finding results consistent with standard cosmological models and constraining deviations on sub-galactic scales.

Contribution

It provides the first constraints on the primordial matter power spectrum at very small scales using lensing data, accounting for systematic uncertainties and different halo models.

Findings

Power spectrum amplitude consistent with ΛCDM predictions.

No significant deviations detected at small scales.

Constraints improve understanding of dark matter and inflation models.

Abstract

The primordial matter power spectrum quantifies fluctuations in the distribution of dark matter immediately following inflation. Over cosmic time, over-dense regions of the primordial density field grow and collapse into dark matter halos, whose abundance and density profiles retain memory of the initial conditions. By analyzing the image magnifications in eleven strongly-lensed and quadruply-imaged quasars, we infer the abundance and concentrations of low-mass halos, and cast the measurement in terms of the amplitude of the primordial matter power spectrum. We anchor the power spectrum on large scales, isolating the effect of small-scale deviations from the $\Lambda$CDM prediction. Assuming an analytic model for the power spectrum and accounting for several sources of potential systematic uncertainty, including three different models for the halo mass function, we obtain correlated inferences of $\log_{10}\left(P / P_{\Lambda \rm{CDM}}\right)$, the power spectrum amplitude relative to the predictions of the concordance cosmological model, of $0.0_{-0.4}^{+0.5}$, $0.1_{-0.6}^{+0.7}$, and $0.2_{-0.9}^{+1.0}$ at k = 10, 25 and 50 $\rm{Mpc^{-1}}$ at $68 \%$ confidence, consistent with cold dark matter and single-field slow-roll inflation.