UC Berkeley

The past decade has seen the rise of high-precision cosmological observations accompanied by emerging tensions among various datasets when interpreted within the standard cosmological model (ΛCDM). We investigate how joint analyses of secondary anisotropies in the cosmic microwave background (CMB) and large-scale structure (LSS) surveys can be leveraged to improve the robustness of cosmological inference. In Part I, we develop novel methods for mitigating foreground contamination in CMB lensing reconstruction. Extragalactic foregrounds such as the thermal Sunyaev-Zel’dovich (tSZ) effect and the cosmic infrared background (CIB) can bias lensing estimators, particularly on small scales. We construct bias-hardened quadratic estimators, both in temperature and polarization, that null specific foreground profiles with minimal degradation in signalto-noise. We further generalize temperature-based shear estimators to polarization, finding that the shear-only estimator is a special case of a more general class of large-lens-suppressed estimators. In tandem, we explore optimal multifrequency methods, quantifying the tradeoffs between noise and bias in the presence of extragalactic foregrounds.Part II applies these tools to current datasets, addressing a subset of the aforementioned tensions. We perform a cross-correlation analysis of the latest CMB lensing maps from Planck and ACT with the DESI legacy imaging data, yielding tomographic constraints on linear structure growth. We find overall consistency with ΛCDM, both in the overall amplitude and time-evolution of structure growth. We then present methods to mitigate lensing biases in the mean patchy screening signal around DESI galaxies and show that, when these biases are taken into account, patchy screening is consistent with the baryon distribution inferred from the kinetic SZ effect. Finally, we quantify the impact of the optical depth τ on parameter inference from the CMB, arguing that a higher value of τ would alleviate the preference for beyond-ΛCDM physics by current CMB and BAO data.Part III projects forward to the next generation of large-scale structure surveys. We demonstrate that combining high-redshift galaxy surveys with CMB data from Simons Observatory or a stage-4 CMB survey will enable percent-level constraints on the neutrino mass sum, curvature, light relics, the expansion and growth histories, (early) dark energy, modified gravity and primordial non-Gaussianity. A new method is proposed for using 21 cm clustering to measure τ independently of large-scale CMB measurements. It is shown that future 21 cm interferometers have the potential to measure τ to a higher precision than a cosmic-variance limited CMB survey while at the same time mitigating biases arising from the miss-modeling of the small-scale astrophysics relevant for reionization.Altogether, this work advances the extraction of cosmological information from secondary CMB effects and LSS, addresses key theoretical and observational systematics, and lays a foundation for robust analyses from upcoming datasets.