1806.09530
Note on the Kaiser-Peacock paper regarding gravitational lensing effects
Ellis, Durrer
This paper revisits the controversy concerning whether gravitational lensing effects make a significant difference to estimation of distance to the CMB LSS in cosmology. A recent paper by Kaiser and Peacock supports a previous paper by Weinberg stating that such affects average to zero because of energy conservation. In this note, problems are pointed out in the Kaiser and Peacock analysis related to their choice of endpoint of integration, and to the 'wrinkly surface' argument.
1806.10537
A highly precise shape-noise-free shear bias estimator
Pujol, Kilbinger, Sure, Bobin
Present a new method to estimate shear measurement bias in image sims that significantly improves its precision with respect to the state-of-the art methods. This method is based on measuring the shear response for individual images. Generate sheared versions of the same image to measure how the shape measurement changes with the changes in the shear, so that one obtains a shear response for each original image, as well as its additive bias. Using the exact same noise realizations for each sheared version allows obtaining an exact estimation of its shear response. The estimated shear bias of a sample of galaxies comes from the measured averages of the shear response and individual additive bias. The precision of this method supposes an improvement with respect to previous methods since the method is not affected by shape noise. As a consequence, this method does not require shape noise cancellation for a precise estimation of shear bias. The method can be easily applied to many applications such as shear measurement validation and calibration, reducing the number of necessary simulated images by a few orders of magnitude to achieve the same precision requirements.
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