Assessing the growth of structure over cosmic time with CMB lensing

TL;DR

This paper reviews how CMB lensing and its cross-correlations with galaxy surveys can test the growth of cosmic structure over time, addressing current tensions in cosmological measurements.

Contribution

It provides a comprehensive review of CMB lensing techniques and their potential to clarify discrepancies in structure growth measurements within the standard cosmological model.

Findings

CMB lensing offers a powerful probe of matter fluctuations over cosmic time.

Cross-correlations with galaxy surveys enhance the understanding of structure growth.

Current measurements show tensions that could indicate new physics or systematic errors.

Abstract

The standard $\Lambda$CDM cosmological model informed by cosmic microwave background (CMB) anisotropies makes a precise prediction for the growth of matter density fluctuations over cosmic time on linear scales. A variety of cosmological observables offer independent and complementary ways of testing this prediction, but results have been mixed, with many constraints on the amplitude of structure $S_8$ being 2-3$\sigma$ lower than the expectation from Planck primary CMB anisotropies. It is currently unclear whether these discrepancies are due to observational systematics, non-linearities and baryonic effects or new physics. We review how gravitational lensing of the CMB has and will continue to provide insights into this problem, including through tomographic cross-correlations with galaxy surveys over cosmic time.