TY - UNPB

T1 - The skewed weak lensing likelihood: why biases arise, despite data and theory being sound

AU - Sellentin, Elena

AU - Heymans, Catherine

AU - Harnois-Déraps, Joachim

PY - 2017/12/14

Y1 - 2017/12/14

N2 - We derive the essentials of the skewed weak lensing likelihood via a
simple Hierarchical Model. Our likelihood passes four objective and
cosmology-independent tests which a standard Gaussian likelihood fails.
We demonstrate that sound weak lensing analyses are naturally biased
low, and this does not indicate any new physics such as deviations from
$\Lambda$CDM. Mathematically, the biases arise because noisy two-point
functions follow skewed distributions. This form of bias is already
known from CMB analyses, where the low multipoles have asymmetric error
bars. Weak lensing is more strongly affected by this asymmetry as
galaxies form a discrete set of shear tracer particles, in contrast to a
smooth shear field. We demonstrate that the biases can be up to 30
percent of the standard deviation per data point, dependent on the
properties of the weak lensing survey. Our likelihood provides a
versatile framework with which to address this bias in future weak
lensing analyses.

AB - We derive the essentials of the skewed weak lensing likelihood via a
simple Hierarchical Model. Our likelihood passes four objective and
cosmology-independent tests which a standard Gaussian likelihood fails.
We demonstrate that sound weak lensing analyses are naturally biased
low, and this does not indicate any new physics such as deviations from
$\Lambda$CDM. Mathematically, the biases arise because noisy two-point
functions follow skewed distributions. This form of bias is already
known from CMB analyses, where the low multipoles have asymmetric error
bars. Weak lensing is more strongly affected by this asymmetry as
galaxies form a discrete set of shear tracer particles, in contrast to a
smooth shear field. We demonstrate that the biases can be up to 30
percent of the standard deviation per data point, dependent on the
properties of the weak lensing survey. Our likelihood provides a
versatile framework with which to address this bias in future weak
lensing analyses.

KW - Astrophysics - Cosmology and Nongalactic Astrophysics

M3 - Working paper

BT - The skewed weak lensing likelihood: why biases arise, despite data and theory being sound

PB - ArXiv

ER -