Reconstructing Small Scale Lenses from the Cosmic Microwave Background Temperature Fluctuations

Understand

Cosmic Microwave Background (CMB) lensing is a powerful probe of the matter distribution in the Universe.

• The standard quadratic estimator, which is typically used to measure the lensing signal, is known to be suboptimal for low-noise polarization data from next-generation experiments.
• In this paper we explain why the quadratic estimator will also be suboptimal for measuring lensing on very small scales, even for measurements in temperature where this estimator typically performs well.
• Though maximum likelihood methods could be implemented to improve performance, we explore a much simpler solution, revisiting a previously proposed method to measure lensing which involves a direct inversion of the background gradient.