A new filter to better map the dark universe:

[beecee]

https://phys.org/news/2019-05-filter-dark-universe.html

A new filter to better map the dark universe

by Glenn Roberts Jr., Lawrence Berkeley National Laboratory

Just as a wine glass distorts an image showing temperature fluctuations in the cosmic microwave background in this photo illustration, large objects like galaxy clusters and galaxies can similarly distort this light to produce lensing effects. Credit: Emmanuel Schaan and Simone Ferraro/Berkeley Lab

The earliest known light in our universe, known as the cosmic microwave background, was emitted about 380,000 years after the Big Bang. The patterning of this relic light holds many important clues to the development and distribution of large-scale structures such as galaxies and galaxy clusters.

Distortions in the cosmic microwave background(CMB), caused by a phenomenon known as lensing, can further illuminate the structure of the universe and can even tell us things about the mysterious, unseen universe—including dark energy, which makes up about 68 percent of the universe and accounts for its accelerating expansion, and dark matter, which accounts for about 27 percent of the universe.

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the paper:

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.181301

Foreground-Immune Cosmic Microwave Background Lensing with Shear-Only Reconstruction:

 

ABSTRACT:

Cosmic microwave background (CMB) lensing from current and upcoming wide-field CMB experiments such as AdvACT, SPT-3G and Simons Observatory relies heavily on temperature (versus polarization). In this regime, foreground contamination to the temperature map produces significant lensing biases, which cannot be fully controlled by multifrequency component separation, masking, or bias hardening. In this Letter, we split the standard CMB lensing quadratic estimator into a new set of optimal “multipole” estimators. On large scales, these multipole estimators reduce to the known magnification and shear estimators, and a new shear B-mode estimator. We leverage the different symmetries of the lensed CMB and extragalactic foregrounds to argue that the shear-only estimator should be approximately immune to extragalactic foregrounds. We build a new method to compute, separately and without noise, the primary, secondary, and trispectrum biases to CMB lensing from foreground simulations. Using this method, we demonstrate that the shear estimator is, indeed, insensitive to extragalactic foregrounds, even when applied to a single-frequency temperature map contaminated with cosmic infrared background, thermal Sunyaev-Zel’dovich, kinematic Sunyaev-Zel’dovich, and radio point sources. This dramatic reduction in foreground biases allows us to include higher temperature multipoles than with the standard quadratic estimator, thus, increasing the total lensing signal-to-noise ratio beyond the quadratic estimator. In addition, magnification-only and shear B-mode estimators provide useful diagnostics for potential residuals.