1712.04923
The skewed weak lensing likelihood: why biases arise, despite data and theory being sound
Sellentin, Heymans, Harnois-Déraps
Derive the essential so f the skewed WL likelihood via a simple Hierarchical Model. The likelihood passes 4 objective and cosmology-independent tests which a standard Gaussian likelihood fails. Demonstrate that sound WL analysis are naturally biased low, and this does not indicate any new physics such as deviations from LCDM. Mathematically, the biases arise because noisy 2pt functions follow skewed distributions. This form of bias is already known from CMB analyses, where the low multiples have asymmetric error bars. WL is more strongly affected by this asymmetry as galaxies form a discrete set of shear tracer particles, in contrast to a smooth shear field. Demonstrate that the biases can be up to 30% of the standard deviation per data point, dependent on the properties of the WL survey. The likelihood provides a versatile framework with which to address this bias in future WL analyses.
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