# Internal delensing of Planck CMB temperature and polarization

## TL;DR

This paper demonstrates the first internal delensing of Planck CMB temperature and polarization maps, showing significant sharpening of acoustic peaks and a measurable reduction in lensing effects, confirming predictions of the standard cosmological model.

## Contribution

The paper presents the first successful internal delensing of Planck CMB data, including polarization, using quadratic estimates and displacement fields, achieving high significance detections.

## Key findings

- Delensing sharpens acoustic peaks in the power spectrum.
- Significant detection of delensing effects in polarization and temperature spectra.
- Reduction of lensing power in B-mode maps by 7% at 4.5 sigma significance.

## Abstract

We present a first internal delensing of CMB maps, both in temperature and polarization, using the public foreground-cleaned (SMICA) Planck 2015 maps. After forming quadratic estimates of the lensing potential, we use the corresponding displacement field to undo the lensing on the same data. We build differences of the delensed spectra to the original data spectra specifically to look for delensing signatures. After taking into account reconstruction noise biases in the delensed spectra, we find an expected sharpening of the power spectrum acoustic peaks with a delensing efficiency of $29\,\%$ ($TT$) $25\,\%$ ($TE$) and $22\,\%$ ($EE$). The detection significance of the delensing effects is very high in all spectra: $12\,\sigma$ in $EE$ polarization; $18\,\sigma$ in $TE$; and $20\,\sigma$ in $TT$. The null hypothesis of no lensing in the maps is rejected at $26\,\sigma$. While direct detection of the power in lensing $B$-modes themselves is not possible at high significance at Planck noise levels, we do detect (at $4.5\,\sigma$ under the null hypothesis) delensing effects in the $B$-mode map, with $7\,\%$ reduction in lensing power. Our results provide a first demonstration of polarization delensing, and generally of internal CMB delensing, and stand in agreement with the baseline $\Lambda$CDM Planck 2015 cosmology expectations.