Small-correlated-against-large estimator for the lensing of the cosmic microwave background

Weak gravitational lensing of the cosmic microwave background (CMB) carries imprints of the physics operating at redshifts much lower than that of recombination and serves as an important probe of cosmological structure formation, dark matter physics, and the mass of neutrinos. Reconstruction of the CMB lensing deflection field through use of quadratic estimators has proven successful with existing data, but is known to be suboptimal on small angular scales (& ell;>3000) for experiments with low-noise levels. Future experiments will provide better observations in this regime, but these techniques will remain statistically limited by their approximations. We show that correlations between fluctuations of the large-scale temperature gradient power of the CMB sourced by & ell;<2000 and fluctuations of the local small-scale temperature power reveal a lensing signal that is prominent in even the real-space pixel statistics across a CMB temperature map. We present the development of the small-correlated-against-large estimator (SCALE), a novel estimator for the CMB lensing spectrum that offers promising complementary analysis alongside other reconstruction techniques in this regime. The SCALE method computes correlations between both the large-/small-scale temperature gradient power in harmonic space, and it is able to quantitatively recover unbiased statistics of the CMB lensing field without the need for map-level reconstruction. SCALE can outperform quadratic estimator signal-to-noise by a factor of up to 1.5 in current and upcoming experiments for CMB lensing power spectra C-6000更多