Elisabeth Krause, Peter Schneider, Tim Eifler
Decomposing the shear signal into E and B-modes properly, i.e. without
leakage of B-modes into the E-mode signal and vice versa, has been a
long-standing problem in weak gravitational lensing. At the two-point level
this problem was resolved by developing the so-called ring statistics, and
later the COSEBIs; however, extending these concepts to the three-point level
is far from trivial. Currently used methods to decompose three-point shear
correlation functions (3PCFs) into E- and B-modes require knowledge of the 3PCF
down to arbitrary small scales. This implies that the 3PCF needs to be modeled
on scales smaller than the minimum separation of 2 galaxies and subsequently
will be biased towards the model, or, in the absence of a model, the statistics
is affected by E/B-mode leakage (or mixing). In this paper we derive a new
third-order E/B-mode statistic that performs the decomposition using the 3PCF
only on a finite interval, and thereby is free of any E/B-mode leakage while at
the same time relying solely on information from the data. In addition, we
relate this third-order ring statistics to the convergence field, thereby
enabling a fast and convenient calculation of this statistic from numerical
simulations. We note that our new statistics should be applicable to
corresponding E/B-mode separation problems in the CMB polarization field.
View original:
http://arxiv.org/abs/1201.4752
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