Unified and Consistent Structure Growth Measurements from Joint ACT, SPT, and <i>Planck</i> CMB Lensing

We present the tightest cosmic microwave background (CMB) lensing constraints to date on the growth of structure by combining CMB lensing measurements from the Atacama Cosmology Telescope (ACT), the South Pole Telescope (SPT), and Planck. Each of these surveys individually provides lensing measurements with similarly high statistical power, achieving signal-to-noise ratios of approximately 40. The combined lensing band powers represent the most precise CMB lensing power spectrum measurement to date with a signal-to-noise ratio of 61 and an amplitude of A_{lens}^{recon}=1.025±0.017 with respect to the theory prediction from the best-fit CMB Planck-ACT cosmology. The band powers from all three lensing datasets, analyzed jointly, yield a 1.6% measurement of the parameter combination S_{8}^{CMBL}≡σ_{8}(Ω_{m}/0.3)^{0.25}=0.825_{-0.013}^{+0.015}. Including dark energy spectroscopic instrument baryon acoustic oscillation (BAO) data improves the constraint on the amplitude of matter fluctuations to σ_{8}=0.829±0.009 (a 1.1% determination). When combining with uncalibrated supernovae from Pantheon+, we present a 4% sound-horizon-independent estimate of H_{0}=66.4±2.5 km s^{-1} Mpc^{-1}. The joint lensing constraints on structure growth and present-day Hubble rate are fully consistent with a ΛCDM model fit to the primary CMB data from Planck and ACT. While the precise upper limit is sensitive to the choice of data and underlying model assumptions, when varying the neutrino mass sum within the ΛCDM cosmological model, the combination of primary CMB, BAO, and CMB lensing drives the probable upper limit for the mass sum towards lower values, comparable to the minimum mass prior required by neutrino oscillation experiments.