Small Correlated Against Large Estimator (SCALE) for Cosmic Microwave Background Lensing

TL;DR

The paper introduces SCALE, a new estimator for CMB lensing that leverages correlations between large-scale temperature gradients and small-scale fluctuations, improving accuracy and signal detection over traditional quadratic methods.

Contribution

SCALE is a novel estimator that uses real-space pixel statistics to recover unbiased CMB lensing signals without map-level reconstruction, outperforming quadratic estimators in certain regimes.

Findings

SCALE can outperform quadratic estimators by up to 1.5 times in signal-to-noise ratio.

It effectively recovers unbiased lensing statistics without requiring map-level reconstruction.

The method is promising for future high-resolution CMB experiments.

Abstract

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 sub-optimal 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 to the local small-scale temperature power reveal a lensing signal which 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 which 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 $C_{6000<L<8000}^{\phi\phi}$.